OBERHEIM SYNTH

Hi guys, a new Matrix 6 owner here!
I bought this beauty two weeks ago. The unit worked great for this two weeks, but yesterday it started to act weirdly: when i turn the unit on, after a variable time (from zero to let say a couple of minutes) some voice gets stuck, amd eventually notes arw triggered in a random way. 
An important note here is the fact that this happens only on patches with the keyboard patch option to "reassign", not to "rotate".
Does anyone here have by hand some schematics to share? Any idea which chip could be the cultript? 
I need some guidance to figure the logic of this thing...
Thanks in advance!

Hi

 

Service manual is here:   http://www.deepsonic.ch/deep/docs_manuals/oberheim_matrix-6_service_manual.pdf

 

I don’t know specifically especially with very limited information but after fixing a bunch of synths, including my Matrix 6 I would say always start with checking the power supply.  Make sure the voltages are pretty close. That is the cause of a LOT of weird problems!

 

Scott

From: oberheim@yahoogroups.com [mailto:oberheim@yahoogroups.com] 
Sent: March 14, 2019 2:41 AM
To: oberheim@yahoogroups.com
Subject: [oberheim] Matrix 6 voice stuck issue

 

  

Hi guys, a new Matrix 6 owner here!
I bought this beauty two weeks ago. The unit worked great for this two weeks, but yesterday it started to act weirdly: when i turn the unit on, after a variable time (from zero to let say a couple of minutes) some voice gets stuck, amd eventually notes arw triggered in a random way. 
An important note here is the fact that this happens only on patches with the keyboard patch option to "reassign", not to "rotate".
Does anyone here have by hand some schematics to share? Any idea which chip could be the cultript? 
I need some guidance to figure the logic of this thing...
Thanks in advance!

Thanks. Sorry for the limited amount of info but I will add info along the way. Voltages are ok. I have not used the oscilloscope to see eventual fluctuations thou and a cap replacement is scheduled.
One thing I would like to understand is what could cause notes triggering. I mean: where do the "trigger note" inputs coming from the keyboard and midi in go? Which chip computes the keyboard matrix and midi in signal? Because i think I should start probing there...
Thanks!

The seevice manual you posted is the low quality (almost unreadable) service manual available everywhere online ;)
I am in the hunt for a better quality scan.

A friend of mine suggested me that the issue could be software related: variable stucks, non predictable behaviour... and perfect voltages. I then decided to place the old v2.13 firware the synth came with. Well, it's working now and I have no issues now. I will toy with the unit for so e day and see if i found the solution. 
Have anyone here ever had strange issues with tauntek firwwares? I burned two of those v2.15 firmwares on different 27256 eproms and both are defective someway, even if verified...

Is the EPROM checksum correct?  It should be 2036H.
Also, what access time EPROMs are you using?

Bob

--------------------------------------------
On Fri, 3/15/19, baritonomarchetto@... [oberheim] <oberheim@yahoogroups.com> wrote:

 Subject: [oberheim] Re: Matrix 6 voice stuck issue
 To: oberheim@yahoogroups.com
 Date: Friday, March 15, 2019, 4:56 PM
 
 A friend of mine suggested me
 that the issue could be software related: variable stucks,
 non predictable behaviour... and perfect voltages. I then
 decided to place the old v2.13 firware the synth came with.
 Well, it's working now and I have no issues now. I will
 toy with the unit for so e day and see if i found the
 solution. 
 Have anyone here ever had strange
 issues with tauntek firwwares? I burned two of those v2.15
 firmwares on different 27256 eproms and both are defective
 someway, even if verified...
 
 ------------------------------------
 Posted by: baritonomarchetto@...
 ------------------------------------
 
 
 ------------------------------------
 
 Yahoo Groups Links
 
 
 Traditional
 
     (Yahoo! ID required)
 
     oberheim-fullfeatured@yahoogroups.com

I am burning 1:1 tauntek firmware without modifying checksums (i don't even know how I could do it with my GQ4X, to be honest).
I used 27256 eproms I had by hand: what should be the maximum access time of the eprom? 
I really want to place back the 2.15 firmware because dramatically increase the time response of filter cutoff and other parameters...
(Thanks guys!)

Hi Flavio, I am located in Veneto, Italy

Could you please give me a more detailed list of chips I should replace? The "wrong eprom" solution was not really a solution in the end and i am going to order caps from rs online fo a full recap.
Thankyou!

Kurt, what are these analog switches you refer to? 
Consider that I have both an oscope and logic probe so I can test the logics before replacing chips ;)

Waiting for some help on the "logic" side of these boards (cpu and voices) I have decided to rebuilt the power supply first, replacing caps and voltage regulators (I read somewhere that those are prone to fail...). Shooting components is not my modus operandi, but without decent schematics and some support I have no other choices.
I will let you know if this will be sufficient ;)

Well well well, good news! I finally had all the components in my mailbox. Replaced all electrolitics and voltage regulators and, voilà, the machine is working as it should! I would bet those 78005 where the culript... Read somewhere thwy are prone to fault. Replace them with common 7805.
Now I will play my MX6 for some week to see if the solution is rock solid ;)
If you will not read me on this topic, good, everything is fine.
The final message: if the behaviour ofnyour matrix 6 is strange, refurbish your power supply first!

Guys, I own a Matrix1000 that has a proplem in stucking one voice randomly. I always thought it was because of an Ic or a capacitor on the components board inside it, but maybe I should work on the power supplier, before worring for something else. Thanks a lot!

Inviato da Yahoo Mail su Android

Guys, I am still here :(
After rebuilding the PSU I had some day of "pause", then yesterday I had the time to play my matrix: after one hour the issue was back again... doh.
Today I made some additional test:
- voltages are ok (eh...)
- the issue is better described as a freeze of the synth, not a voice stuck: the keys you are pressing when it freezes stay on, but everything is no more responsive
- If I remove the ribbon connector on the voice board (before turning the machine on) after some variable time the issue appears, so I am prone to locate the problem on the cpu board
It's definitely a faulty component because the synth works starting cold.
Any suggestion on how to track the issue would be appreciated. I am suffering soo much :(

Today I had another session with m matrix 6: played for one hour, more or less, then the issue reappeared. So, the culript could be a slowly but inesorably IC going too hot...
I have just bought a new 68B09 cpu from a chinese seller: in one month time it will be at my place and I will replace the old processor and all the caps on the cpu board, just in case. Let's see if this will be sufficient.
Any help would be much appreciated (is anyone still reading me? :) )
Thanks!

Mondovermona, thank you for your help. I wrote my latest post without reading tour answer so, yes, someone is still reading me :)
I made the tapping test you are suggesting, but after the issue appear. It could be a good idea to perform it before, in order to indue the issue. I will do that.
About the oscilloscope: yes, I have a 100MHz tektronics so I can definitely check if the cpu is running when the issue appear. The thing is I dont know which pin to check and what should I read... Any help on this would be much appreciated.

I don’t really have any ideas right now but I will say watch some of synth chaser’s videos and it might help. Checking the clock might be a good start. If it stops supplying a clock signal to the processor everything would stop. That might not be completely accurate because I haven’t had to deal with a problem like that myself so I don’t know much about it but it might be something to think about. Watch this video and look for others like it.

 

https://youtu.be/zcdh_Hbzq7g?t=652

 

Scott

From: oberheim@yahoogroups.com [mailto:oberheim@yahoogroups.com] 
Sent: March 31, 2019 3:31 PM
To: oberheim@yahoogroups.com
Subject: [oberheim] Re: Matrix 6 voice stuck issue

 

  

Mondovermona, thank you for your help. I wrote my latest post without reading tour answer so, yes, someone is still reading me :)
I made the tapping test you are suggesting, but after the issue appear. It could be a good idea to perform it before, in order to indue the issue. I will do that.
About the oscilloscope: yes, I have a 100MHz tektronics so I can definitely check if the cpu is running when the issue appear. The thing is I dont know which pin to check and what should I read... Any help on this would be much appreciated.

Check and replace the capacitors in the power supply first! You can use a hair dryer while it’s not acting up and if it is a capacitor, it will show up quickly while heating up.Richard


Sent from Yahoo Mail for iPad


On Sunday, March 31, 2019, 3:39 PM, 'Scott Rogers' scott@scottfromcanada.com [oberheim] <oberheim@yahoogroups.com> wrote:

    


I don’t really have any ideas right now but I will say watch some of synth chaser’s videos and it might help. Checking the clock might be a good start. If it stops supplying a clock signal to the processor everything would stop. That might not be completely accurate because I haven’t had to deal with a problem like that myself so I don’t know much about it but it might be something to think about. Watch this video and look for others like it.

  

https://youtu.be/zcdh_Hbzq7g?t=652

  

Scott

From: oberheim@yahoogroups.com [mailto:oberheim@yahoogroups.com] 
Sent: March 31, 2019 3:31 PM
To: oberheim@yahoogroups.com
Subject: [oberheim] Re: Matrix 6 voice stuck issue

  

  

Mondovermona, thank you for your help. I wrote my latest post without reading tour answer so, yes, someone is still reading me :)
I made the tapping test you are suggesting, but after the issue appear. It could be a good idea to perform it before, in order to indue the issue. I will do that.
About the oscilloscope: yes, I have a 100MHz tektronics so I can definitely check if the cpu is running when the issue appear. The thing is I dont know which pin to check and what should I read... Any help on this would be much appreciated.

Hi Richard, as I wrote: I have just replaced all the caps (and voltage refulators) in the psu. This increased the time i can play with no issue, but did not solve completely.

Just turned on the machine, pressed/moved every single transistor and chip on the cpu board, but I couldnt accelerate the insorgence of the issue: rock solid responses from the unit. Not sure if this is good or not at this point :)
I need to investigate further the 68B09 clock thing

The 68B09 is a someway special evolution of the 6809 with INTERNAL clock generation. I suspect it cannot be monitored then.
Anyway, a replacement cpu will pop in my mailbox in one month (or two...).
Will keep you posted, but please feel free to suggest me tests to slim down the possibilities area. Thanks!

Thank you. Could you please give me some additional detail on what to check? Is it right to assume that if the reset pin is high (no reset) some data transfer activity should be recorded? Which one is the chip enable pin? The halt pin eventually? I could not figure it out on the datasheet :(
I need some guide on this, never ever had to fight with a cpu...
Also, in the schematics i see only the connection to U15 (ls245), is that chip the one i should focus on?
(Thanks for the help everyone)

The M6 schematic clearly shows a clocks crystal between pins 38 and 39, though.

On the other hand the M6 schematic isn't 100% trustworthy in my opinion...


On 01 Apr 2019 10:42:13 +0000
"baritonomarchetto@... [oberheim]" <oberheim@yahoogroups.com> wrote:

> The 68B09 is a someway special evolution of the 6809 with INTERNAL clock generation. I suspect it cannot be monitored then.
> Anyway, a replacement cpu will pop in my mailbox in one month (or two...).
> Will keep you posted, but please feel free to suggest me tests to slim down the possibilities area. Thanks!
> 
> ------------------------------------
> Posted by: baritonomarchetto@...
> ------------------------------------
> 
> 
> ------------------------------------
-- 
M.R. <gacki@...>

Yes, you are right, sorry for the wrong info i gave. In my little experience I have never seen a crystal go bad (nor a microprocessor of this era, to say the truth), but this issue is so uncommon to me...
Will try some probing in a week or two
Thnak you all!

Does anyone know the value of the clock crystal?