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2012-11-27 by doug1052365
I'm trying to repair this OB-Xa w/JL Cooper MIDI. Has no sound, all LEDs are flickering, buttons don't change anything. The power supply is OK. It seems the CPU is not booting up. Does anyone have an image of the Diagnostic EPROM? Thanks Doug
2012-11-27 by Paulo Palmieri
----- Original Message -----From: doug1052365Sent: Tuesday, November 27, 2012 5:43 PMSubject: [oberheim] OB-Xa Diagnostic EPROM neededI'm trying to repair this OB-Xa w/JL Cooper MIDI.
Has no sound, all LEDs are flickering, buttons don't change anything.
The power supply is OK. It seems the CPU is not booting up.
Does anyone have an image of the Diagnostic EPROM?
Thanks
Doug
2012-11-28 by Doug
Yes, my best guess is that it is a bad EPROM. Unfortunately I don't have the image files for the MIDI version. I have image files for the original so I tried to remove the MIDI board and put in the original EPROMs. There was no flickering but no sound either. I'm not sure if i need to change anything else to revert it to original non-MIDI. So a set of image files for the MIDI version would be useful too. Doug
> Posted by: "Paulo Palmieri" paulopalmieri@... souldream70 > Date: Tue Nov 27, 2012 11:58 am ((PST)) > > I don\ufffdt have the eprom but have an OB-Xa with the same problem. > In my case the buttons are working but the leds are flickering too and after 20 minutes they light off... > I suppose that this could be an Eprom problem??? > > Paulo > > > > ----- Original Message ----- > From: doug1052365 > To: oberheim@yahoogroups.com > Sent: Tuesday, November 27, 2012 5:43 PM > Subject: [oberheim] OB-Xa Diagnostic EPROM needed > > > > I'm trying to repair this OB-Xa w/JL Cooper MIDI. > Has no sound, all LEDs are flickering, buttons don't change anything. > The power supply is OK. It seems the CPU is not booting up. > Does anyone have an image of the Diagnostic EPROM? > > Thanks > > Doug > > > > > > > > Messages in this topic (2) > > > > > > ------------------------------------------------------------------------ > Yahoo! Groups Links > > > > ------------------------------------------------------------------------ >
2012-11-28 by Martin Ator
It's probably something to do with the Midi mod so have a look around for anything suspicious, wires/broken tracks etc. It's very rare that you get problems with an Eprom, they are very tough. If you can read them with a programmer then UV erase them, then re-program them any problems will show up. Having said all this however, static is an enemy of us all. It depends how safe you are in this respect as to what possibilities may arise during troubleshooting. It is much more likely that another IC is damaged/has been damaged by static or other reason/age etc, the main cause possibly being problems created during the installation of the Midi mod. EEproms (Eproms that aren't ceramic with a little erase window) can develop problems over time as they are erased/programmed with much lower voltages.I would not expect an OB to have these types installed. I don't have any OB series synths. If there is a back-up memory system involved, then a big candidate for suspicion are the memory chips involved as any hint of static while checking the battery or replacing it is liable to damage the memory chips. I would look here first for problems if it was me. ________________________________ From: Doug <dmeek@...> To: oberheim@yahoogroups.com Sent: Wednesday, 28 November 2012, 14:09 Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed Yes, my best guess is that it is a bad EPROM. Unfortunately I don't have the image files for the MIDI version. I have image files for the original so I tried to remove the MIDI board and put in the original EPROMs. There was no flickering but no sound either. I'm not sure if i need to change anything else to revert it to original non-MIDI. So a set of image files for the MIDI version would be useful too. Doug
> Posted by: "Paulo Palmieri" paulopalmieri@... souldream70 > Date: Tue Nov 27, 2012 11:58 am ((PST)) > > I don´t have the eprom but have an OB-Xa with the same problem. > In my case the buttons are working but the leds are flickering too and after 20 minutes they light off... > I suppose that this could be an Eprom problem??? > > Paulo > > > > ----- Original Message ----- > From: doug1052365 > To: oberheim@yahoogroups.com > Sent: Tuesday, November 27, 2012 5:43 PM > Subject: [oberheim] OB-Xa Diagnostic EPROM needed > > > > I'm trying to repair this OB-Xa w/JL Cooper MIDI. > Has no sound, all LEDs are flickering, buttons don't change anything. > The power supply is OK. It seems the CPU is not booting up. > Does anyone have an image of the Diagnostic EPROM? > > Thanks > > Doug > > > > > > > > Messages in this topic (2) > > > > > > ---------------------------------------------------------- > Yahoo! Groups Links > > > > ---------------------------------------------------------- >
2012-11-28 by rob hukin
Yes, my best guess is that it is a bad EPROM. Unfortunately I don't have
the image files for the MIDI version. I have image files for the
original so I tried to remove the MIDI board and put in the original
EPROMs. There was no flickering but no sound either. I'm not sure
if i need to change anything else to revert it to original non-MIDI.
So a set of image files for the MIDI version would be useful too.
Doug
> Posted by: "Paulo Palmieri" paulopalmieri@... souldream70
> Date: Tue Nov 27, 2012 11:58 am ((PST))
>
> I don´t have the eprom but have an OB-Xa with the same problem.
> In my case the buttons are working but the leds are flickering too and after 20 minutes they light off...
> I suppose that this could be an Eprom problem???
>
> Paulo
>
>
>
> ----- Original Message -----
> From: doug1052365
> To: oberheim@yahoogroups.com
> Sent: Tuesday, November 27, 2012 5:43 PM
> Subject: [oberheim] OB-Xa Diagnostic EPROM needed
>
>
>
> I'm trying to repair this OB-Xa w/JL Cooper MIDI.
> Has no sound, all LEDs are flickering, buttons don't change anything.
> The power supply is OK. It seems the CPU is not booting up.
> Does anyone have an image of the Diagnostic EPROM?
>
> Thanks
>
> Doug
>
>
>
>
>
>
>
> Messages in this topic (2)
>
>
>
>
>
> ----------------------------------------------------------
> Yahoo! Groups Links
>
>
>
> ----------------------------------------------------------
>
2012-11-29 by Doug
Hi Martin, thanks for your suggestions.
The reason I suspect the EPROM is because of experience with a Textronix
468 digital scope. It was suggested that I replace the EPROMs. I was
sceptical, but did it anyway and it worked!
Nor sure if reading and reprogramming the chips would work. If the OB-Xa
can't read them would the EPROM reader/programmer be any different?
Like you say it would show a bad eprom, then I would need new bin files.
I checked all address and data lines with the scope. They all look ok.
I replaced the UPD780 CPU and 6116 CMOS ram - no change.
I replace the two 2114 RAM chips and there was a difference: there was
no flickering, some random LEDs were on, some buttons had an effect,
some not. Still no sound.
I've posted two photos of the board to the Photos section
Doug
Posted by: "Martin Ator" cyllall@... cyllall
Date: Wed Nov 28, 2012 7:31 am ((PST))
It's probably something to do with the Midi mod so have a look around
for anything suspicious, wires/broken tracks etc.
It's very rare that you get problems with an Eprom, they are very tough.
If you can read them with a programmer then UV erase them, then
re-program them any problems will show up. Having said all this however,
static is an enemy of us all. It depends how safe you are in this
respect as to what possibilities may arise during troubleshooting.
It is much more likely that another IC is damaged/has been damaged by
static or other reason/age etc, the main cause possibly being problems
created during the installation of the Midi mod. EEproms (Eproms that
aren't ceramic with a little erase window) can develop problems over
time as they are erased/programmed with much lower voltages.I would not
expect an OB to have these types installed.
I don't have any OB series synths. If there is a back-up memory system
involved, then a big candidate for suspicion are the memory chips
involved as any hint of static while checking the battery or replacing
it is liable to damage the memory chips. I would look here first for
problems if it was me.2012-11-30 by Scott
I'd go through the two motherboards, pull every socketed chip and clean the pins with an artist's eraser, wipe with alcohol and reinstall before I started troubleshooting. Some of the old Texas Instruments chips are notorious for oxidation problems on the pins. --- In oberheim@yahoogroups.com, "Paulo Palmieri" <paulopalmieri@...> wrote:
> > I don´t have the eprom but have an OB-Xa with the same problem. > In my case the buttons are working but the leds are flickering too and after 20 minutes they light off... > I suppose that this could be an Eprom problem??? > > Paulo > > > > ----- Original Message ----- > From: doug1052365 > To: oberheim@yahoogroups.com > Sent: Tuesday, November 27, 2012 5:43 PM > Subject: [oberheim] OB-Xa Diagnostic EPROM needed > > > > I'm trying to repair this OB-Xa w/JL Cooper MIDI. > Has no sound, all LEDs are flickering, buttons don't change anything. > The power supply is OK. It seems the CPU is not booting up. > Does anyone have an image of the Diagnostic EPROM? > > Thanks > > Doug >
2012-11-30 by Martin Ator
If you have an Eprom reader then there would be no harm in trying to read them off. You can then try and verify the buffer with the Eprom, or look at the read file in a hex viewer. If you have a UV Eprom eraser and can erase the Eprom, then reprogram it with the file you read off and then verify it and all checks out, then it probably isn't the Eprom. Your saying that all the data lines are OK. Check that any buttons aren't shorted especially memory protect ones etc and also check Digital to analogue/analogue to digital sections for correct outputs/flaky zener diodes etc. I have a JX-3P that's giving me similar problems. I'm sure you've checked the power supply but what about the -5volts.That's an easy one to overlook. ________________________________
From: Doug <dmeek@...> To: oberheim@yahoogroups.com Sent: Thursday, 29 November 2012, 20:08 Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed Hi Martin, thanks for your suggestions. The reason I suspect the EPROM is because of experience with a Textronix 468 digital scope. It was suggested that I replace the EPROMs. I was sceptical, but did it anyway and it worked! Nor sure if reading and reprogramming the chips would work. If the OB-Xa can't read them would the EPROM reader/programmer be any different? Like you say it would show a bad eprom, then I would need new bin files. I checked all address and data lines with the scope. They all look ok. I replaced the UPD780 CPU and 6116 CMOS ram - no change. I replace the two 2114 RAM chips and there was a difference: there was no flickering, some random LEDs were on, some buttons had an effect, some not. Still no sound. I've posted two photos of the board to the Photos section Doug Posted by: "Martin Ator" cyllall@... cyllall Date: Wed Nov 28, 2012 7:31 am ((PST)) It's probably something to do with the Midi mod so have a look around for anything suspicious, wires/broken tracks etc. It's very rare that you get problems with an Eprom, they are very tough. If you can read them with a programmer then UV erase them, then re-program them any problems will show up. Having said all this however, static is an enemy of us all. It depends how safe you are in this respect as to what possibilities may arise during troubleshooting. It is much more likely that another IC is damaged/has been damaged by static or other reason/age etc, the main cause possibly being problems created during the installation of the Midi mod. EEproms (Eproms that aren't ceramic with a little erase window) can develop problems over time as they are erased/programmed with much lower voltages.I would not expect an OB to have these types installed. I don't have any OB series synths. If there is a back-up memory system involved, then a big candidate for suspicion are the memory chips involved as any hint of static while checking the battery or replacing it is liable to damage the memory chips. I would look here first for problems if it was me.
2012-11-30 by wesleyknick
OB-Xa EPROM image (Rev C) is available here if interested: http://www.lazyblueoctopus.com/html/oberheim.html --- In oberheim@yahoogroups.com, Martin Ator <cyllall@...> wrote:
> > If you have an Eprom reader then there would be no harm in trying to read them off. You can then try and verify the buffer with the Eprom, or look at the read file in a hex viewer. If you have a UV Eprom eraser and can erase the Eprom, then reprogram it with the file you read off and then verify it and all checks out, then it probably isn't the Eprom. > > Your saying that all the data lines are OK. Check that any buttons aren't shorted especially memory protect ones etc and also check Digital to analogue/analogue to digital sections for correct outputs/flaky zener diodes etc. > I have a JX-3P that's giving me similar problems. > I'm sure you've checked the power supply but what about the -5volts.That's an easy one to overlook. > > > > ________________________________ > From: Doug <dmeek@...> > To: oberheim@yahoogroups.com > Sent: Thursday, 29 November 2012, 20:08 > Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed > > > Â > Hi Martin, thanks for your suggestions. > > The reason I suspect the EPROM is because of experience with a Textronix > 468 digital scope. It was suggested that I replace the EPROMs. I was > sceptical, but did it anyway and it worked! > Nor sure if reading and reprogramming the chips would work. If the OB-Xa > can't read them would the EPROM reader/programmer be any different? > Like you say it would show a bad eprom, then I would need new bin files. > I checked all address and data lines with the scope. They all look ok. > I replaced the UPD780 CPU and 6116 CMOS ram - no change. > I replace the two 2114 RAM chips and there was a difference: there was > no flickering, some random LEDs were on, some buttons had an effect, > some not. Still no sound. > > I've posted two photos of the board to the Photos section > > Doug > > Posted by: "Martin Ator" cyllall@... cyllall > Date: Wed Nov 28, 2012 7:31 am ((PST)) > > It's probably something to do with the Midi mod so have a look around > for anything suspicious, wires/broken tracks etc. > > It's very rare that you get problems with an Eprom, they are very tough. > If you can read them with a programmer then UV erase them, then > re-program them any problems will show up. Having said all this however, > static is an enemy of us all. It depends how safe you are in this > respect as to what possibilities may arise during troubleshooting. > > It is much more likely that another IC is damaged/has been damaged by > static or other reason/age etc, the main cause possibly being problems > created during the installation of the Midi mod. EEproms (Eproms that > aren't ceramic with a little erase window) can develop problems over > time as they are erased/programmed with much lower voltages.I would not > expect an OB to have these types installed. > > I don't have any OB series synths. If there is a back-up memory system > involved, then a big candidate for suspicion are the memory chips > involved as any hint of static while checking the battery or replacing > it is liable to damage the memory chips. I would look here first for > problems if it was me. >
2012-12-03 by synthparts
Those B5 ROMs are for the OB-8 not OB-Xa. Anyway I have the ROMs for the OB-Xa with JL Cooper MIDI and Rev C processor board if you need it. Doug synthparts.com --- In oberheim@yahoogroups.com, rob hukin <robhukin@...> wrote:
> > Hi Doug, > > The B5 images are available from Magnus Danielson's site - http://rubidium.dyndns.org/~magnus/synths/companies/oberheim/ > > rob. > > On 28 Nov 2012, at 14:09, Doug wrote: > > > Yes, my best guess is that it is a bad EPROM. Unfortunately I don't have > > the image files for the MIDI version. I have image files for the > > original so I tried to remove the MIDI board and put in the original > > EPROMs. There was no flickering but no sound either. I'm not sure > > if i need to change anything else to revert it to original non-MIDI. > > > > So a set of image files for the MIDI version would be useful too. > > > > Doug > > > > > Posted by: "Paulo Palmieri" paulopalmieri@... souldream70 > > > Date: Tue Nov 27, 2012 11:58 am ((PST)) > > > > > > I don´t have the eprom but have an OB-Xa with the same problem. > > > In my case the buttons are working but the leds are flickering too and after 20 minutes they light off... > > > I suppose that this could be an Eprom problem??? > > > > > > Paulo > > > > > > > > > > > > ----- Original Message ----- > > > From: doug1052365 > > > To: oberheim@yahoogroups.com > > > Sent: Tuesday, November 27, 2012 5:43 PM > > > Subject: [oberheim] OB-Xa Diagnostic EPROM needed > > > > > > > > > > > > I'm trying to repair this OB-Xa w/JL Cooper MIDI. > > > Has no sound, all LEDs are flickering, buttons don't change anything. > > > The power supply is OK. It seems the CPU is not booting up. > > > Does anyone have an image of the Diagnostic EPROM? > > > > > > Thanks > > > > > > Doug > > > > > > > > > > > > > > > > > > > > > > > > Messages in this topic (2) > > > > > > > > > > > > > > > > > > ---------------------------------------------------------- > > > Yahoo! Groups Links > > > > > > > > > > > > ---------------------------------------------------------- > > > > > >
2012-12-03 by Doug
Since I don't own this keyboard I may have to call it a day soon.
I tried removing the MIDI board and burning the 3 EPROMs from
http://www.lazyblueoctopus.com/html/oberheim.html. Still no go.
Some LEDs stay lit, some are flickering, most are off and the
buttons do nothing. Curiously the LEDs and buttons on the Bender
panel have always worked. However it appears the problem is not
the EPROMs. So I'm back to my original request: Diagnostic EPROM.
I'll keep the keyboard for another week, then return to customer.
Thank you to everyone for the suggestions. The one about a stuck
button was a good one, I've seen it before. But not this time.
Doug
1a. Re: OB-Xa Diagnostic EPROM needed
Posted by: "synthparts" synthparts@... synthparts
Date: Mon Dec 3, 2012 1:58 am ((PST))
Those B5 ROMs are for the OB-8 not OB-Xa. Anyway I have the ROMs for the
OB-Xa with JL Cooper MIDI and Rev C processor board if you need it.
Doug
synthparts.com2012-12-04 by wesleyknick
Doug, I've been following the email traffic on this issue rather sporadically however now that you've described in detail again I can certainly say I have a funny feeling the crystal on the upper control board is bad (next to the memory protect switch). If the quartz crystal oscillator next to the processor IC chip is bad, the processor will process nothing as it sets the processor speed which if I recall correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise if it doesn't set the correct processor speed either. I own two OB-Xa's at the moment and one of the two exhibited exactly the same symptoms you are describing - some of the LEDs will illuminate when the unit is powered on but will not respond to the buttons, and the modulation panel will still seem to function normally. Power on, off and back on again will sometimes change the configuration of LEDs that light up but the unit will still seem frozen and not respond to the buttons. I had the very almost identical problem a didn't realize the crystal was bad unit I removed the upper and lower control boards and heard something rattling next to the memory protect switch. The quartz crystal inside the housing had physically broken off an was rattling around. Sounded like a miniature cow bell. Swapped it out and the OB-Xa's worked great ever since. Took me a while to figure the crystal was the problem and I got so frustrated I wanted to just give it up and hang it from my Christmas tree as it was about the only thing I could think of to do with the pretty LEDs that would light up on the top it and do nothing else. Try changing the crystal and see if that does anything... I recently repaired a Matrix 6 with this similar issue. --- In oberheim@yahoogroups.com, Doug <dmeek@...> wrote:
> > Since I don't own this keyboard I may have to call it a day soon. > I tried removing the MIDI board and burning the 3 EPROMs from > http://www.lazyblueoctopus.com/html/oberheim.html. Still no go. > Some LEDs stay lit, some are flickering, most are off and the > buttons do nothing. Curiously the LEDs and buttons on the Bender > panel have always worked. However it appears the problem is not > the EPROMs. So I'm back to my original request: Diagnostic EPROM. > I'll keep the keyboard for another week, then return to customer. > Thank you to everyone for the suggestions. The one about a stuck > button was a good one, I've seen it before. But not this time. > > Doug > > > > > > 1a. Re: OB-Xa Diagnostic EPROM needed > Posted by: "synthparts" synthparts@... synthparts > Date: Mon Dec 3, 2012 1:58 am ((PST)) > > Those B5 ROMs are for the OB-8 not OB-Xa. Anyway I have the ROMs for the > OB-Xa with JL Cooper MIDI and Rev C processor board if you need it. > > Doug > synthparts.com >
2012-12-04 by Martin Ator
It's got to be something easily overlooked. There's so many socketed IC's maybe a pin has been bent over etc. I would check the X-tal. The system isn't booting up properly. I don't think the diagnostic Eproms would help in this situation. Put a new crystal in anyway and if there are any little @15pf caps on the crystal check them as well. ________________________________ From: wesleyknick <wesknick@...> To: oberheim@yahoogroups.com Sent: Tuesday, 4 December 2012, 0:43 Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed Doug, I've been following the email traffic on this issue rather sporadically however now that you've described in detail again I can certainly say I have a funny feeling the crystal on the upper control board is bad (next to the memory protect switch). If the quartz crystal oscillator next to the processor IC chip is bad, the processor will process nothing as it sets the processor speed which if I recall correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise if it doesn't set the correct processor speed either. I own two OB-Xa's at the moment and one of the two exhibited exactly the same symptoms you are describing - some of the LEDs will illuminate when the unit is powered on but will not respond to the buttons, and the modulation panel will still seem to function normally. Power on, off and back on again will sometimes change the configuration of LEDs that light up but the unit will still seem frozen and not respond to the buttons. I had the very almost identical problem a didn't realize the crystal was bad unit I removed the upper and lower control boards and heard something rattling next to the memory protect switch. The quartz crystal inside the housing had physically broken off an was rattling around. Sounded like a miniature cow bell. Swapped it out and the OB-Xa's worked great ever since. Took me a while to figure the crystal was the problem and I got so frustrated I wanted to just give it up and hang it from my Christmas tree as it was about the only thing I could think of to do with the pretty LEDs that would light up on the top it and do nothing else. Try changing the crystal and see if that does anything... I recently repaired a Matrix 6 with this similar issue. --- In oberheim@yahoogroups.com, Doug <dmeek@...> wrote:
> > Since I don't own this keyboard I may have to call it a day soon. > I tried removing the MIDI board and burning the 3 EPROMs from > http://www.lazyblueoctopus.com/html/oberheim.html. Still no go. > Some LEDs stay lit, some are flickering, most are off and the > buttons do nothing. Curiously the LEDs and buttons on the Bender > panel have always worked. However it appears the problem is not > the EPROMs. So I'm back to my original request: Diagnostic EPROM. > I'll keep the keyboard for another week, then return to customer. > Thank you to everyone for the suggestions. The one about a stuck > button was a good one, I've seen it before. But not this time. > > Doug > > > > > > 1a. Re: OB-Xa Diagnostic EPROM needed > Posted by: "synthparts" synthparts@... synthparts > Date: Mon Dec 3, 2012 1:58 am ((PST)) > > Those B5 ROMs are for the OB-8 not OB-Xa. Anyway I have the ROMs for the > OB-Xa with JL Cooper MIDI and Rev C processor board if you need it. > > Doug > synthparts.com >
2012-12-04 by Martin Ator
Just looked at the schematic and it doesn't have the usual way of putting capacitors on each leg. Don't forget to double check the little reset hold circuit on the Z80. ________________________________ From: Martin Ator <cyllall@...> To: "oberheim@yahoogroups.com" <oberheim@yahoogroups.com> Sent: Tuesday, 4 December 2012, 0:55 Subject: Re: [oberheim] Re: OB-Xa Diagnostic EPROM needed It's got to be something easily overlooked. There's so many socketed IC's maybe a pin has been bent over etc. I would check the X-tal. The system isn't booting up properly. I don't think the diagnostic Eproms would help in this situation. Put a new crystal in anyway and if there are any little @15pf caps on the crystal check them as well. ________________________________ From: wesleyknick <wesknick@...> To: oberheim@yahoogroups.com Sent: Tuesday, 4 December 2012, 0:43 Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed Doug, I've been following the email traffic on this issue rather sporadically however now that you've described in detail again I can certainly say I have a funny feeling the crystal on the upper control board is bad (next to the memory protect switch). If the quartz crystal oscillator next to the processor IC chip is bad, the processor will process nothing as it sets the processor speed which if I recall correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise if it doesn't set the correct processor speed either. I own two OB-Xa's at the moment and one of the two exhibited exactly the same symptoms you are describing - some of the LEDs will illuminate when the unit is powered on but will not respond to the buttons, and the modulation panel will still seem to function normally. Power on, off and back on again will sometimes change the configuration of LEDs that light up but the unit will still seem frozen and not respond to the buttons. I had the very almost identical problem a didn't realize the crystal was bad unit I removed the upper and lower control boards and heard something rattling next to the memory protect switch. The quartz crystal inside the housing had physically broken off an was rattling around. Sounded like a miniature cow bell. Swapped it out and the OB-Xa's worked great ever since. Took me a while to figure the crystal was the problem and I got so frustrated I wanted to just give it up and hang it from my Christmas tree as it was about the only thing I could think of to do with the pretty LEDs that would light up on the top it and do nothing else. Try changing the crystal and see if that does anything... I recently repaired a Matrix 6 with this similar issue. --- In oberheim@yahoogroups.com, Doug <dmeek@...> wrote:
> > Since I don't own this keyboard I may have to call it a day soon. > I tried removing the MIDI board and burning the 3 EPROMs from > http://www.lazyblueoctopus.com/html/oberheim.html. Still no go. > Some LEDs stay lit, some are flickering, most are off and the > buttons do nothing. Curiously the LEDs and buttons on the Bender > panel have always worked. However it appears the problem is not > the EPROMs. So I'm back to my original request: Diagnostic EPROM. > I'll keep the keyboard for another week, then return to customer. > Thank you to everyone for the suggestions. The one about a stuck > button was a good one, I've seen it before. But not this time. > > Doug > > > > > > 1a. Re: OB-Xa Diagnostic EPROM needed > Posted by: "synthparts" synthparts@... synthparts > Date: Mon Dec 3, 2012 1:58 am ((PST)) > > Those B5 ROMs are for the OB-8 not OB-Xa. Anyway I have the ROMs for the > OB-Xa with JL Cooper MIDI and Rev C processor board if you need it. > > Doug > synthparts.com >
2012-12-04 by Doug
The crystal was Ok. Measured 2.456 MHz at pin 6 Z80
(divided by 2 by IC A116). CPU reset circuit is OK
A Christmas tree ornament sounds like a good idea.
Doug
1b. Re: OB-Xa Diagnostic EPROM needed
Posted by: "wesleyknick" wesknick@... wesleyknick
Date: Mon Dec 3, 2012 4:43 pm ((PST))
Doug, I've been following the email traffic on this issue rather
sporadically however now that you've described in detail again I can
certainly say I have a funny feeling the crystal on the upper control
board is bad (next to the memory protect switch). If the quartz crystal
oscillator next to the processor IC chip is bad, the processor will
process nothing as it sets the processor speed which if I recall
correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise
if it doesn't set the correct processor speed either. I own two OB-Xa's
at the moment and one of the two exhibited exactly the same symptoms you
are describing - some of the LEDs will illuminate when the unit is
powered on but will not respond to the buttons, and the modulation panel
will still seem to function normally. Power on, off and back on again
will sometimes change the configuration of LEDs that light up but the
unit will still seem frozen and not respond to the buttons. I had the
very almost identical problem a didn't realize the crystal was bad unit
I removed the upper and lower control boards and heard something
rattling next to the memory protect switch. The quartz crystal inside
the housing had physically broken off an was rattling around. Sounded
like a miniature cow bell. Swapped it out and the OB-Xa's worked great
ever since. Took me a while to figure the crystal was the problem and I
got so frustrated I wanted to just give it up and hang it from my
Christmas tree as it was about the only thing I could think of to do
with the pretty LEDs that would light up on the top it and do nothing
else. Try changing the crystal and see if that does anything... I
recently repaired a Matrix 6 with this similar issue.2012-12-04 by Martin Ator
What is the function of the LM311 in the circuit? (If I had a teleporter I could pop round with my Boardmaster 4000) ________________________________
From: Doug <dmeek@...> To: oberheim@yahoogroups.com Sent: Tuesday, 4 December 2012, 19:11 Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed The crystal was Ok. Measured 2.456 MHz at pin 6 Z80 (divided by 2 by IC A116). CPU reset circuit is OK A Christmas tree ornament sounds like a good idea. Doug 1b. Re: OB-Xa Diagnostic EPROM needed Posted by: "wesleyknick" wesknick@... wesleyknick Date: Mon Dec 3, 2012 4:43 pm ((PST)) Doug, I've been following the email traffic on this issue rather sporadically however now that you've described in detail again I can certainly say I have a funny feeling the crystal on the upper control board is bad (next to the memory protect switch). If the quartz crystal oscillator next to the processor IC chip is bad, the processor will process nothing as it sets the processor speed which if I recall correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise if it doesn't set the correct processor speed either. I own two OB-Xa's at the moment and one of the two exhibited exactly the same symptoms you are describing - some of the LEDs will illuminate when the unit is powered on but will not respond to the buttons, and the modulation panel will still seem to function normally. Power on, off and back on again will sometimes change the configuration of LEDs that light up but the unit will still seem frozen and not respond to the buttons. I had the very almost identical problem a didn't realize the crystal was bad unit I removed the upper and lower control boards and heard something rattling next to the memory protect switch. The quartz crystal inside the housing had physically broken off an was rattling around. Sounded like a miniature cow bell. Swapped it out and the OB-Xa's worked great ever since. Took me a while to figure the crystal was the problem and I got so frustrated I wanted to just give it up and hang it from my Christmas tree as it was about the only thing I could think of to do with the pretty LEDs that would light up on the top it and do nothing else. Try changing the crystal and see if that does anything... I recently repaired a Matrix 6 with this similar issue.
2012-12-04 by wesleyknick
Call me a dummy cause I'm certainly stumped... Sorry to hear my suggestion didn't pinpoint the issue. Anything can be fixed just some problems take longer to solve than others. If all else fails, try swaptronics. Get a good OB-Xa to use as a test bed and swap suspected faulty components into it, a technique that works at the component level as well as the assembly (PCB) level. When the normally functional instrument exhibits the same problem, you'll know you've isolated the component. Sometimes the component you think is the problem isn't really but the result of a problem further upstream (ie., the power supply). I've made some strange discoveries doing swaptronics and on more than one occassion just found it to be something as simple as a bad connector. Just trying to offer some advice... --- In oberheim@yahoogroups.com, Martin Ator <cyllall@...> wrote:
> > What is the function of the LM311 in the circuit? > (If I had a teleporter I could pop round with my Boardmaster 4000) > > > > > ________________________________ > From: Doug <dmeek@...> > To: oberheim@yahoogroups.com > Sent: Tuesday, 4 December 2012, 19:11 > Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed > > > Â > The crystal was Ok. Measured 2.456 MHz at pin 6 Z80 > (divided by 2 by IC A116). CPU reset circuit is OK > A Christmas tree ornament sounds like a good idea. > > Doug > > 1b. Re: OB-Xa Diagnostic EPROM needed > Posted by: "wesleyknick" wesknick@... wesleyknick > Date: Mon Dec 3, 2012 4:43 pm ((PST)) > > Doug, I've been following the email traffic on this issue rather > sporadically however now that you've described in detail again I can > certainly say I have a funny feeling the crystal on the upper control > board is bad (next to the memory protect switch). If the quartz crystal > oscillator next to the processor IC chip is bad, the processor will > process nothing as it sets the processor speed which if I recall > correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise > if it doesn't set the correct processor speed either. I own two OB-Xa's > at the moment and one of the two exhibited exactly the same symptoms you > are describing - some of the LEDs will illuminate when the unit is > powered on but will not respond to the buttons, and the modulation panel > will still seem to function normally. Power on, off and back on again > will sometimes change the configuration of LEDs that light up but the > unit will still seem frozen and not respond to the buttons. I had the > very almost identical problem a didn't realize the crystal was bad unit > I removed the upper and lower control boards and heard something > rattling next to the memory protect switch. The quartz crystal inside > the housing had physically broken off an was rattling around. Sounded > like a miniature cow bell. Swapped it out and the OB-Xa's worked great > ever since. Took me a while to figure the crystal was the problem and I > got so frustrated I wanted to just give it up and hang it from my > Christmas tree as it was about the only thing I could think of to do > with the pretty LEDs that would light up on the top it and do nothing > else. Try changing the crystal and see if that does anything... I > recently repaired a Matrix 6 with this similar issue. >
2012-12-05 by Les Lambert
I can't help you directly with your problem, but wanted to add a note of caution.
If a problem in your current OBXa has been caused by a defective component that has then taken something else out, swoppertronics will take your functioning machine into the dumpster too.
any swopping of parts that are not clearly marked as to which was the good one is doomed to disappoint.
A visual inspection and comparison to an identical machine is a great help to an acute observer, but unless you have a clue what might cause your symptoms you may be heading into darkness.
The service manuals of equipment from this era are essential but an understanding of the various functions of many of the components involved is assumed.
Another assumption was the age of the components. I'm not sure anybody actually knew what was going to happen when 1980s electronics aged 40 years.
The connectors aren't really that good either, and these may need a work-around requiring a good level of wiring skills suitable for the particular style of construction used.
An experienced service engineer who specialises in your particular instrument is required.
Repeat - Required.
The technique of swopping with a known good part was good in its time and place, but I have to remind myself when I first open a defective item just which techniques are applicable. A 12AX7 swop for example doesn't usually put anything in any great danger, but a shorted power tube can destroy yourMarshall tube sockets, or MK2 Boogie or V4B output tube pcb if you move it around.
Enthusiasm and confidence are a good thing to have on your side, but caution and care are often required to balance them.
Nobody can expect instant success every time without studying the problem and considering the options.
If you are used to a power tool, doing things by hand seems pedestrian, but it could be better approach and yield a superior result. Your decision, but sometimes a small amount of thought can prevent a disaster.
--- On Tue, 4/12/12, wesleyknick <wesknick@gmail.com> wrote:
From: wesleyknick <wesknick@...>
Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed
To: oberheim@yahoogroups.com
Date: Tuesday, 4 December, 2012, 23:16
Call me a dummy cause I'm certainly stumped... Sorry to hear my suggestion didn't pinpoint the issue. Anything can be fixed just some problems take longer to solve than others. If all else fails, try swaptronics. Get a good OB-Xa to use as a test bed and swap suspected faulty components into it, a technique that works at the component level as well as the assembly (PCB) level. When the normally functional instrument exhibits the same problem, you'll know you've isolated the component. Sometimes the component you think is the problem isn't really but the result of a problem further upstream (ie., the power supply). I've made some strange discoveries doing swaptronics and on more than one occassion just found it to be something as simple as a bad connector. Just trying to offer some advice...
--- In oberheim@yahoogroups.com, Martin Ator <cyllall@...> wrote:> > What is the function of the LM311 in the circuit? > (If I had a teleporter I could pop round with my Boardmaster 4000) > > > > > ________________________________ > From: Doug <dmeek@...> > To: oberheim@yahoogroups.com > Sent: Tuesday, 4 December 2012, 19:11 > Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed > > > Â > The crystal was Ok. Measured 2.456 MHz at pin 6 Z80 > (divided by 2 by IC A116). CPU reset circuit is OK > A Christmas tree ornament sounds like a good idea. > > Doug > > 1b. Re: OB-Xa Diagnostic EPROM needed > Posted by: "wesleyknick" wesknick@... wesleyknick > Date: Mon Dec 3, 2012 4:43 pm ((PST)) > > Doug, I've been following the email traffic on this issue rather > sporadically however now that you've described in detail again I can > certainly say I have a funny feeling the crystal on the upper control > board is bad (next to the memory protect switch). If the quartz crystal > oscillator next to the processor IC chip is bad, the processor will > process nothing as it sets the processor speed which if I recall > correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise > if it doesn't set the correct processor speed either. I own two OB-Xa's > at the moment and one of the two exhibited exactly the same symptoms you > are describing - some of the LEDs will illuminate when the unit is > powered on but will not respond to the buttons, and the modulation panel > will still seem to function normally. Power on, off and back on again > will sometimes change the configuration of LEDs that light up but the > unit will still seem frozen and not respond to the buttons. I had the > very almost identical problem a didn't realize the crystal was bad unit > I removed the upper and lower control boards and heard something > rattling next to the memory protect switch. The quartz crystal inside > the housing had physically broken off an was rattling around. Sounded > like a miniature cow bell. Swapped it out and the OB-Xa's worked great > ever since. Took me a while to figure the crystal was the problem and I > got so frustrated I wanted to just give it up and hang it from my > Christmas tree as it was about the only thing I could think of to do > with the pretty LEDs that would light up on the top it and do nothing > else. Try changing the crystal and see if that does anything... I > recently repaired a Matrix 6 with this similar issue. >
2012-12-05 by Steve.S
1.)check for any solder shorts on EPROM and CPU
2.) meter top pins of EPROMs to the underneath of the PCB connections for IC socket tests, likewise the CPU
best,
Steve
--- On Wed, 5/12/12, Les Lambert <les_lmbrt@yahoo.co.uk> wrote:
From: Les Lambert <les_lmbrt@...>
Subject: Re: [oberheim] Re: OB-Xa Repairs.
To: oberheim@yahoogroups.com
Received: Wednesday, 5 December, 2012, 10:14 PM
I can't help you directly with your problem, but wanted to add a note of caution.
If a problem in your current OBXa has been caused by a defective component that has then taken something else out, swoppertronics will take your functioning machine into the dumpster too.
any swopping of parts that are not clearly marked as to which was the good one is doomed to disappoint.
A visual inspection and comparison to an identical machine is a great help to an acute observer, but unless you have a clue what might cause your symptoms you may be heading into darkness.
The service manuals of equipment from this era are essential but an understanding of the various functions of many of the components involved is assumed.
Another assumption was the age of the components. I'm not sure anybody actually knew what was going to happen when 1980s electronics
aged 40 years.
The connectors aren't really that good either, and these may need a work-around requiring a good level of wiring skills suitable for the particular style of construction used.
An experienced service engineer who specialises in your particular instrument is required.
Repeat - Required.
The technique of swopping with a known good part was good in its time and place, but I have to remind myself when I first open a defective item just which techniques are applicable. A 12AX7 swop for example doesn't usually put anything in any great danger, but a shorted power tube can destroy yourMarshall tube sockets, or MK2 Boogie or V4B output tube pcb if you move it around.
Enthusiasm and confidence are a good thing to have on your side, but caution and care are often required to balance them.
Nobody can expect instant success every time without studying the problem and considering the options.
If you are used to a
power tool, doing things by hand seems pedestrian, but it could be better approach and yield a superior result. Your decision, but sometimes a small amount of thought can prevent a disaster.
--- On Tue, 4/12/12, wesleyknick <wesknick@...> wrote:
From: wesleyknick <wesknick@...>
Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed
To: oberheim@yahoogroups.com
Date: Tuesday, 4 December, 2012, 23:16
Call me a dummy cause I'm certainly stumped... Sorry to hear my suggestion didn't pinpoint the issue. Anything can be fixed just some problems take longer to solve than others. If all else fails, try swaptronics. Get a good OB-Xa to use as a test bed and swap suspected faulty components into it, a technique that works at the component level as well as the assembly (PCB) level. When the normally functional instrument exhibits the same problem, you'll know you've isolated the component. Sometimes the component you think is the problem isn't really but the result of a problem further upstream (ie., the power supply). I've made some strange discoveries doing swaptronics and on more than one occassion just found it to be something as simple as a bad connector. Just trying to offer some advice...
--- In oberheim@yahoogroups.com, Martin Ator <cyllall@...> wrote:> > What is the function of the LM311 in the circuit? > (If I had a teleporter I could pop round with my Boardmaster 4000) > > > > > ________________________________ > From: Doug <dmeek@...> > To: oberheim@yahoogroups.com > Sent: Tuesday, 4 December 2012, 19:11 > Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed > > > Â > The crystal was Ok. Measured 2.456 MHz at pin 6 Z80 > (divided by 2 by IC A116). CPU reset circuit is OK > A Christmas tree ornament sounds like a good idea. > > Doug > > 1b. Re: OB-Xa Diagnostic EPROM needed > Posted by: "wesleyknick" wesknick@... wesleyknick > Date: Mon Dec 3, 2012 4:43 pm ((PST)) > > Doug, I've been following the email traffic on this issue rather > sporadically however now that you've described in detail again I can > certainly say I have a funny feeling the crystal on the upper control > board is bad (next to the memory protect switch). If the quartz crystal > oscillator next to the processor IC chip is bad, the processor will > process nothing as it sets the processor speed which if I recall > correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise > if it doesn't set the correct processor speed either. I own two OB-Xa's > at the moment and one of the two exhibited exactly the same symptoms you > are describing - some of the LEDs will illuminate when the unit is > powered on but will not respond to the buttons, and the modulation panel > will still seem to function normally. Power on, off and back on again > will sometimes change the configuration of LEDs that light up but the > unit will still seem frozen and not respond to the buttons. I had the > very almost identical problem a didn't realize the crystal was bad unit > I removed the upper and lower control boards and heard something > rattling next to the memory protect switch. The quartz crystal inside > the housing had physically broken off an was rattling around. Sounded > like a miniature cow bell. Swapped it out and the OB-Xa's worked great > ever since. Took me a while to figure the crystal was the problem and I > got so frustrated I wanted to just give it up and hang it from my > Christmas tree as it was about the only thing I could think of to do > with the pretty LEDs that would light up on the top it and do nothing > else. Try changing the crystal and see if that does anything... I > recently repaired a Matrix 6 with this similar issue. >
2013-06-27 by leavesstillgreen
Did you ever figure this out? I'm bringing an OBX back from the dead...like really dead...as in corroded, and probably a previous home to rats. Geeze it's a mess. Mine actually started making sound sometimes, after fixing the socket that the z80 was in. But the front panel is still non-responsive except for a few things. I completely rebuilt the power supply, so that is rock solid. The edit,manual and auto buttons make it do weird things...volume and master tune work...mod wheel works, and the octave switch....some of the randomized patches that come up when booted have working portamento/noise/sample+hold/cross-mod/unison and it cycles through the 4 voices just fine, though they are certainly out of tune. Some success.... I'm guessing some of the Eproms must be working in order for me to be able to play the random patches....but I don't really know enough. I'm not sure where to go from here though.... I don't own an oscilloscope, only a DMM...and no eprom programmer... Any advice welcome! Thanks! For now I will probably recap more of it and change out more cmos chips. I guess I should try replacing the memory chips. --- In oberheim@yahoogroups.com, "wesleyknick" <wesknick@...> wrote:
> > Call me a dummy cause I'm certainly stumped... Sorry to hear my suggestion didn't pinpoint the issue. Anything can be fixed just some problems take longer to solve than others. If all else fails, try swaptronics. Get a good OB-Xa to use as a test bed and swap suspected faulty components into it, a technique that works at the component level as well as the assembly (PCB) level. When the normally functional instrument exhibits the same problem, you'll know you've isolated the component. Sometimes the component you think is the problem isn't really but the result of a problem further upstream (ie., the power supply). I've made some strange discoveries doing swaptronics and on more than one occassion just found it to be something as simple as a bad connector. Just trying to offer some advice... > > --- In oberheim@yahoogroups.com, Martin Ator <cyllall@> wrote: > > > > What is the function of the LM311 in the circuit? > > (If I had a teleporter I could pop round with my Boardmaster 4000) > > > > > > > > > > ________________________________ > > From: Doug <dmeek@> > > To: oberheim@yahoogroups.com > > Sent: Tuesday, 4 December 2012, 19:11 > > Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed > > > > > > Â > > The crystal was Ok. Measured 2.456 MHz at pin 6 Z80 > > (divided by 2 by IC A116). CPU reset circuit is OK > > A Christmas tree ornament sounds like a good idea. > > > > Doug > > > > 1b. Re: OB-Xa Diagnostic EPROM needed > > Posted by: "wesleyknick" wesknick@ wesleyknick > > Date: Mon Dec 3, 2012 4:43 pm ((PST)) > > > > Doug, I've been following the email traffic on this issue rather > > sporadically however now that you've described in detail again I can > > certainly say I have a funny feeling the crystal on the upper control > > board is bad (next to the memory protect switch). If the quartz crystal > > oscillator next to the processor IC chip is bad, the processor will > > process nothing as it sets the processor speed which if I recall > > correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise > > if it doesn't set the correct processor speed either. I own two OB-Xa's > > at the moment and one of the two exhibited exactly the same symptoms you > > are describing - some of the LEDs will illuminate when the unit is > > powered on but will not respond to the buttons, and the modulation panel > > will still seem to function normally. Power on, off and back on again > > will sometimes change the configuration of LEDs that light up but the > > unit will still seem frozen and not respond to the buttons. I had the > > very almost identical problem a didn't realize the crystal was bad unit > > I removed the upper and lower control boards and heard something > > rattling next to the memory protect switch. The quartz crystal inside > > the housing had physically broken off an was rattling around. Sounded > > like a miniature cow bell. Swapped it out and the OB-Xa's worked great > > ever since. Took me a while to figure the crystal was the problem and I > > got so frustrated I wanted to just give it up and hang it from my > > Christmas tree as it was about the only thing I could think of to do > > with the pretty LEDs that would light up on the top it and do nothing > > else. Try changing the crystal and see if that does anything... I > > recently repaired a Matrix 6 with this similar issue. > > >
2013-06-27 by Paulo Palmieri
----- Original Message -----From: leavesstillgreenSent: Thursday, June 27, 2013 5:41 AMSubject: [oberheim] Re: OB-Xa Diagnostic EPROM neededDid you ever figure this out? I'm bringing an OBX back from the dead...like really dead...as in corroded, and probably a previous home to rats. Geeze it's a mess.
Mine actually started making sound sometimes, after fixing the socket that the z80 was in. But the front panel is still non-responsive except for a few things.
I completely rebuilt the power supply, so that is rock solid. The edit,manual and auto buttons make it do weird things...volume and master tune work...mod wheel works, and the octave switch....some of the randomized patches that come up when booted have working portamento/noise/sample+hold/cross-mod/unison and it cycles through the 4 voices just fine, though they are certainly out of tune. Some success....
I'm guessing some of the Eproms must be working in order for me to be able to play the random patches....but I don't really know enough.
I'm not sure where to go from here though.... I don't own an oscilloscope, only a DMM...and no eprom programmer...
Any advice welcome!
Thanks!
For now I will probably recap more of it and change out more cmos chips. I guess I should try replacing the memory chips.
--- In oberheim@yahoogroups.com, "wesleyknick" wrote:
>
> Call me a dummy cause I'm certainly stumped... Sorry to hear my suggestion didn't pinpoint the issue. Anything can be fixed just some problems take longer to solve than others. If all else fails, try swaptronics. Get a good OB-Xa to use as a test bed and swap suspected faulty components into it, a technique that works at the component level as well as the assembly (PCB) level. When the normally functional instrument exhibits the same problem, you'll know you've isolated the component. Sometimes the component you think is the problem isn't really but the result of a problem further upstream (ie., the power supply). I've made some strange discoveries doing swaptronics and on more than one occassion just found it to be something as simple as a bad connector. Just trying to offer some advice...
>
> --- In oberheim@yahoogroups.com, Martin Ator > >
> > What is the function of the LM311 in the circuit?
> > (If I had a teleporter I could pop round with my Boardmaster 4000)
> >
> >
> >
> >
> > ________________________________
> > From: Doug
> > To: oberheim@yahoogroups.com
> > Sent: Tuesday, 4 December 2012, 19:11
> > Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed
> >
> >
> > Â
>; > The crystal was Ok. Measured 2.456 MHz at pin 6 Z80
> > (divided by 2 by IC A116). CPU reset circuit is OK
> > A Christmas tree ornament sounds like a good idea.
> >
> > Doug
> >
> > 1b. Re: OB-Xa Diagnostic EPROM needed
> > Posted by: "wesleyknick" wesknick@ wesleyknick
> > Date: Mon Dec 3, 2012 4:43 pm ((PST))
> >
> > Doug, I've been following the email traffic on this issue rather
> > sporadically however now that you've described in detail again I can
> > certainly say I have a funny feeling the crystal on the upper control
> > board is bad (next to the memory protect switch). If the quartz crystal
> > oscillator next to the processor IC chip is bad, the processor will
> > process nothing as it sets the processor speed which if I recall
> > correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise
> > if it doesn't set the correct processor speed either. I own two OB-Xa's
> >; at the moment and one of the two exhibited exactly the same symptoms you
> > are describing - some of the LEDs will illuminate when the unit is
> > powered on but will not respond to the buttons, and the modulation panel
> > will still seem to function normally. Power on, off and back on again
> > will sometimes change the configuration of LEDs that light up but the
> > unit will still seem frozen and not respond to the buttons. I had the
> > very almost identical problem a didn't realize the crystal was bad unit
> > I removed the upper and lower control boards and heard something
> > rattling next to the memory protect switch. The quartz crystal inside
> > the housing had physically broken off an was rattling around. Sounded
> > like a miniature cow bell. Swapped it out and the OB-Xa's worked great
> > ever since. Took me a while to figure the crystal was the problem and I
> >; got so frustrated I wanted to just give it up and hang it from my
> > Christmas tree as it was about the only thing I could think of to do
> > with the pretty LEDs that would light up on the top it and do nothing
> > else. Try changing the crystal and see if that does anything... I
> > recently repaired a Matrix 6 with this similar issue.
> >
>
2013-06-29 by doug1052365
I finally had to give up and return it to my customer. It didn't make sense (or dollars) to continue. If I owned it I would still be poking away at it I guess. One thing I didn't mention before is that the bridge rectifier on the 5V supply was burnt, so maybe some negative voltage could have got on the +5V supply line. I changed every chip on the upper board. The only ones that made any difference were the RAMs. No improvement, just different. Good Luck Doug ps check every button with the ohmeter to make sure they are all working. Corrosion can get in there and cause problems. --- In oberheim@yahoogroups.com, "leavesstillgreen" <errorspending@...> wrote:
> > Did you ever figure this out? I'm bringing an OBX back from the dead...like really dead...as in corroded, and probably a previous home to rats. Geeze it's a mess. > > Mine actually started making sound sometimes, after fixing the socket that the z80 was in. But the front panel is still non-responsive except for a few things. > > I completely rebuilt the power supply, so that is rock solid. The edit,manual and auto buttons make it do weird things...volume and master tune work...mod wheel works, and the octave switch....some of the randomized patches that come up when booted have working portamento/noise/sample+hold/cross-mod/unison and it cycles through the 4 voices just fine, though they are certainly out of tune. Some success.... > > I'm guessing some of the Eproms must be working in order for me to be able to play the random patches....but I don't really know enough. > > I'm not sure where to go from here though.... I don't own an oscilloscope, only a DMM...and no eprom programmer... > > Any advice welcome! > > Thanks! > > For now I will probably recap more of it and change out more cmos chips. I guess I should try replacing the memory chips. > > > > > --- In oberheim@yahoogroups.com, "wesleyknick" <wesknick@> wrote: > > > > Call me a dummy cause I'm certainly stumped... Sorry to hear my suggestion didn't pinpoint the issue. Anything can be fixed just some problems take longer to solve than others. If all else fails, try swaptronics. Get a good OB-Xa to use as a test bed and swap suspected faulty components into it, a technique that works at the component level as well as the assembly (PCB) level. When the normally functional instrument exhibits the same problem, you'll know you've isolated the component. Sometimes the component you think is the problem isn't really but the result of a problem further upstream (ie., the power supply). I've made some strange discoveries doing swaptronics and on more than one occassion just found it to be something as simple as a bad connector. Just trying to offer some advice... > > > > --- In oberheim@yahoogroups.com, Martin Ator <cyllall@> wrote: > > > > > > What is the function of the LM311 in the circuit? > > > (If I had a teleporter I could pop round with my Boardmaster 4000) > > > > > > > > > > > > > > > ________________________________ > > > From: Doug <dmeek@> > > > To: oberheim@yahoogroups.com > > > Sent: Tuesday, 4 December 2012, 19:11 > > > Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed > > > > > > > > > Â > > > The crystal was Ok. Measured 2.456 MHz at pin 6 Z80 > > > (divided by 2 by IC A116). CPU reset circuit is OK > > > A Christmas tree ornament sounds like a good idea. > > > > > > Doug > > > > > > 1b. Re: OB-Xa Diagnostic EPROM needed > > > Posted by: "wesleyknick" wesknick@ wesleyknick > > > Date: Mon Dec 3, 2012 4:43 pm ((PST)) > > > > > > Doug, I've been following the email traffic on this issue rather > > > sporadically however now that you've described in detail again I can > > > certainly say I have a funny feeling the crystal on the upper control > > > board is bad (next to the memory protect switch). If the quartz crystal > > > oscillator next to the processor IC chip is bad, the processor will > > > process nothing as it sets the processor speed which if I recall > > > correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise > > > if it doesn't set the correct processor speed either. I own two OB-Xa's > > > at the moment and one of the two exhibited exactly the same symptoms you > > > are describing - some of the LEDs will illuminate when the unit is > > > powered on but will not respond to the buttons, and the modulation panel > > > will still seem to function normally. Power on, off and back on again > > > will sometimes change the configuration of LEDs that light up but the > > > unit will still seem frozen and not respond to the buttons. I had the > > > very almost identical problem a didn't realize the crystal was bad unit > > > I removed the upper and lower control boards and heard something > > > rattling next to the memory protect switch. The quartz crystal inside > > > the housing had physically broken off an was rattling around. Sounded > > > like a miniature cow bell. Swapped it out and the OB-Xa's worked great > > > ever since. Took me a while to figure the crystal was the problem and I > > > got so frustrated I wanted to just give it up and hang it from my > > > Christmas tree as it was about the only thing I could think of to do > > > with the pretty LEDs that would light up on the top it and do nothing > > > else. Try changing the crystal and see if that does anything... I > > > recently repaired a Matrix 6 with this similar issue. > > > > > >
2013-07-24 by leavesstillgreen
Thanks for the info! I finally did get it semi-working after changing out some 7442's on the upper board and control board and installing the Encore midi kit. A lot of the chips directly underneath the upper board can cause the front panel to lock up just as easily as those on the upper board. Especially the ones feeding the ribbon cable that leads to the pot boards. Still doesn't fully work though. All of the buttons are working but none of the CPU controlled pots are working. And though the OSC 1 pulse wave button does light up when pressed, OSC 1 goes silent instead of turning to pulse for all voices. OSC 2 is fine. Nice to get some control over this thing finally...it even auto-tunes correctly. And 7 out of my 8 voices are functional, with one just having a bad voltage regulator on the -15v rail, so hopefully once I get that part, all 8 voices will be up and running! Can anyone tell me how to remove the knobs on these pots? They do not seem to slide off easily and I don't see anything holding them in place. And any help trouble shooting the non-working pots would be appreciated. It looks like the 3 4051s on the pot boards are important for the pots, but I'm not sure what other component would take down all of the pots at once.. Thanks for any help anyone can offer... --- In oberheim@yahoogroups.com, "doug1052365" <dmeek@...> wrote:
> > I finally had to give up and return it to my customer. It didn't make > sense (or dollars) to continue. If I owned it I would still be poking > away at it I guess. One thing I didn't mention before is that the > bridge rectifier on the 5V supply was burnt, so maybe some negative > voltage could have got on the +5V supply line. I changed every chip on the upper board. The only ones that made any difference were the > RAMs. No improvement, just different. > > Good Luck > > Doug > > ps check every button with the ohmeter to make sure they are all > working. Corrosion can get in there and cause problems. > > > > --- In oberheim@yahoogroups.com, "leavesstillgreen" <errorspending@> wrote: > > > > Did you ever figure this out? I'm bringing an OBX back from the dead...like really dead...as in corroded, and probably a previous home to rats. Geeze it's a mess. > > > > Mine actually started making sound sometimes, after fixing the socket that the z80 was in. But the front panel is still non-responsive except for a few things. > > > > I completely rebuilt the power supply, so that is rock solid. The edit,manual and auto buttons make it do weird things...volume and master tune work...mod wheel works, and the octave switch....some of the randomized patches that come up when booted have working portamento/noise/sample+hold/cross-mod/unison and it cycles through the 4 voices just fine, though they are certainly out of tune. Some success.... > > > > I'm guessing some of the Eproms must be working in order for me to be able to play the random patches....but I don't really know enough. > > > > I'm not sure where to go from here though.... I don't own an oscilloscope, only a DMM...and no eprom programmer... > > > > Any advice welcome! > > > > Thanks! > > > > For now I will probably recap more of it and change out more cmos chips. I guess I should try replacing the memory chips. > > > > > > > > > > --- In oberheim@yahoogroups.com, "wesleyknick" <wesknick@> wrote: > > > > > > Call me a dummy cause I'm certainly stumped... Sorry to hear my suggestion didn't pinpoint the issue. Anything can be fixed just some problems take longer to solve than others. If all else fails, try swaptronics. Get a good OB-Xa to use as a test bed and swap suspected faulty components into it, a technique that works at the component level as well as the assembly (PCB) level. When the normally functional instrument exhibits the same problem, you'll know you've isolated the component. Sometimes the component you think is the problem isn't really but the result of a problem further upstream (ie., the power supply). I've made some strange discoveries doing swaptronics and on more than one occassion just found it to be something as simple as a bad connector. Just trying to offer some advice... > > > > > > --- In oberheim@yahoogroups.com, Martin Ator <cyllall@> wrote: > > > > > > > > What is the function of the LM311 in the circuit? > > > > (If I had a teleporter I could pop round with my Boardmaster 4000) > > > > > > > > > > > > > > > > > > > > ________________________________ > > > > From: Doug <dmeek@> > > > > To: oberheim@yahoogroups.com > > > > Sent: Tuesday, 4 December 2012, 19:11 > > > > Subject: [oberheim] Re: OB-Xa Diagnostic EPROM needed > > > > > > > > > > > > Â > > > > The crystal was Ok. Measured 2.456 MHz at pin 6 Z80 > > > > (divided by 2 by IC A116). CPU reset circuit is OK > > > > A Christmas tree ornament sounds like a good idea. > > > > > > > > Doug > > > > > > > > 1b. Re: OB-Xa Diagnostic EPROM needed > > > > Posted by: "wesleyknick" wesknick@ wesleyknick > > > > Date: Mon Dec 3, 2012 4:43 pm ((PST)) > > > > > > > > Doug, I've been following the email traffic on this issue rather > > > > sporadically however now that you've described in detail again I can > > > > certainly say I have a funny feeling the crystal on the upper control > > > > board is bad (next to the memory protect switch). If the quartz crystal > > > > oscillator next to the processor IC chip is bad, the processor will > > > > process nothing as it sets the processor speed which if I recall > > > > correctly is 4.9152 MHz on the OB-Xa. The same problem can also arise > > > > if it doesn't set the correct processor speed either. I own two OB-Xa's > > > > at the moment and one of the two exhibited exactly the same symptoms you > > > > are describing - some of the LEDs will illuminate when the unit is > > > > powered on but will not respond to the buttons, and the modulation panel > > > > will still seem to function normally. Power on, off and back on again > > > > will sometimes change the configuration of LEDs that light up but the > > > > unit will still seem frozen and not respond to the buttons. I had the > > > > very almost identical problem a didn't realize the crystal was bad unit > > > > I removed the upper and lower control boards and heard something > > > > rattling next to the memory protect switch. The quartz crystal inside > > > > the housing had physically broken off an was rattling around. Sounded > > > > like a miniature cow bell. Swapped it out and the OB-Xa's worked great > > > > ever since. Took me a while to figure the crystal was the problem and I > > > > got so frustrated I wanted to just give it up and hang it from my > > > > Christmas tree as it was about the only thing I could think of to do > > > > with the pretty LEDs that would light up on the top it and do nothing > > > > else. Try changing the crystal and see if that does anything... I > > > > recently repaired a Matrix 6 with this similar issue. > > > > > > > > > >