Vintage Synth Repair

>
> First off, there's several types of power supplies.  The type that plugs into the wall and converts 120VAC (220vac in UK and Europe) to, generally, +5VDC and +12/-12VDC regulated. Versus those that have a transformer wall-wart that plugs into the wall and delivers between 9 and 15 Volts AC to the unit.  If you have the 120VAC version (there's a wall plug coming from the Simmons) then trace out the high 120VAC paths on the power supply circuit board.  Don't touch these copper lines with your fingers with the power on.
>    The high voltage usually goes to a small internal transformer to be converted to about 12 volts AC.  Then some diodes, bridge rectifiers, and high value electrolytic capacitors to make plus and minus DC.  Then to the voltage regulators like the 7805 and 7806.  The 7805 type of regulators are very common.  They shut down when too much current makes them too hot.  Commonly used in 1980's electronic equipment.  If the 7805 is putting out less than 4.9 volts then something is drawing too much current.
>   I'm at work and can't continue.  Try bringing it to a local Robotics Club meeting, or the Electronics club or students group at the local community college.
> 
> From: xjnx0x <concken@...>
> To: vintagesynthrepair@yahoogroups.com 
> Sent: Tuesday, April 24, 2012 8:58 AM
> Subject: [vintagesynthrepair] Simmons SDE
> 
> HI, I'm new to the list.  
> 
> I have a beloved Simmons SDE that started acting flaky circa 1998.  The SDE is a 6 voice, 4-op FM percussion synthesizer midi rack unit.  At the time it would fail to start up when turned on, but I could coax it into working by flipping it on and off a few times.  Eventually this didn't work anymore and I retired it.. it sat in the corner of my studio for about 12 years... Recently I decided I missed it terribly, I opened it up and found some blown caps in the power supply.  I replaced these and got the unit to turn on again.  It now powers up nicely and all the functions on the front seem to work just fine, responds to midi, responds to button presses, responds to knob movements on the display (only through about half of their range), but there is no sound except for an intermittent buzzing.  
> 
> I took it into a local shop on Saturday, they didn't know what it was and they didn't want to mess with it, told me to try reloading the patches... I'm pretty sure that's not the problem because the patches are at least half unchangeable presets which I assume would be stored in ROM.. If this thing is to live again, its is up to me to raise it from the dead.  I can't find schematics for it anywhere.  
> 
> So I looked up the Yamaha FM chips... The datasheet says they need 5v, minimum 4.8v, but I measured the voltage between pin 1 and 21 and they are only getting 4.5v.  
> 
> Because of this, I'm suspecting the PS has more problems that need to be addressed and I think that's the place to start.  I'm hoping, fingers crossed, that the PS going out and me flipping it on and off like a dumbass, didn't fry any of the output circuitry.
> 
> There are 3 ICs in the PS, a 7805, a 7806, and another one I can't remember off the top of my head right now (88xx something?) but it has the same package as the two voltage regulators.  All three of these were at one time bonded to a little aluminum tray inside the case for a heat sink.  I don't remember if there were still bonded when I opened it up, but they are not bonded now as I had to remove the board to replace the caps.  I've tried to make sure they are in contact with the aluminium whenever I power it up but I don't have thermal contact paste and they and the transformer coil do get pretty hot.  The datasheet says the 7805 can't deliver as much current when its not heat sink-ed (heat sunk??) I'd assume this is the case for the others as well.  
> 
> So, how should I go about troubleshooting the PS circuit, without a schematic or even knowledge of what the voltages are supposed to be?  Any suggestions for dissipating the heat with something temporary? (I'm sure it will be taken apart a few more times before its fixed.)  Anything I should watch out for?  Could the ICs not being in thermal contact have hurt them?  Could the PS going bad have damaged other parts of the machine?  
> 
> I have some experience soldering and building things, but don't mess with power supplies much because frankly they kinda scare me.  
> 
> 
> 
> 
> 
> ------------------------------------
> 
> Yahoo! Groups Links
> 
> 
> 
>     http://docs.yahoo.com/info/terms/
>

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Alan Probandt
Sent: 25 April 2012 00:22
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Re: Simmons SDE

 

  

The description sounds like a linear power supply as were common for music
gear in the mid 1980s.  In the 1990s small units (between 500 milliAmps and
1 Amp) began using switching power supplies.  The switchers run cooler and
more efficiently, but are more complicated.

   Generally test power supplies under full load.  In this case with the
rest of the unit attached.  But if the 7805 voltage is stable +5v with the
ribbon cable disconnected then some chip or part is  pulling more current
than it is supposed to.

If there is no sound except a buzzing, check if the buzzing is 60 or 120
Hertz.  If so, then power supply ripple voltage from the AC mains is getting
through to the output.   The output stage is usually an op-amp with plus and
minus voltages.  Check if there is voltage on the power pins of the op-amp.
Try running the chip numbers through google.  You'll get directed to the
data sheet companies but you can also get data sheets for older parts from
the manufacturer web sites.

  If nothing works, try selling it on eBay.  People there do pay real money
for broken equipment.

 

From: xjnx0x <concken@...>
To: vintagesynthrepair@yahoogroups.com 
Sent: Tuesday, April 24, 2012 1:13 PM
Subject: [vintagesynthrepair] Re: Simmons SDE


Thanks for your reply, to clarify the power supply is 120V input and is
built into the unit on its own little PC board with little plastic offset
clips, inside an aluminum sub-chassis which also contains the transformer.
I can also see plenty of large diodes on the board which are probably part
of the bridge rectifier.  

My idea for the next course of action tonight was testing the input and
output legs of each of the ICs to see what they're delivering.  Should this
be done with the rest of the unit connected via the ribbon cable, or
disconnected?  Will the presence/absence of the rest of the unit affect the
operation of the power supply?  

thanks for your help.  I'll look into an electronics club... good idea.  

Christian

--- In vintagesynthrepair@yahoogroups.com, Alan Probandt <alan_probandt@...>
wrote:
>
> First off, there's several types of power supplies.  The type that plugs
into the wall and converts 120VAC (220vac in UK and Europe) to, generally,
+5VDC and +12/-12VDC regulated. Versus those that have a transformer
wall-wart that plugs into the wall and delivers between 9 and 15 Volts AC to
the unit.  If you have the 120VAC version (there's a wall plug coming from
the Simmons) then trace out the high 120VAC paths on the power supply
circuit board.  Don't touch these copper lines with your fingers with the
power on.
>    The high voltage usually goes to a small internal transformer to be
converted to about 12 volts AC.  Then some diodes, bridge rectifiers, and
high value electrolytic capacitors to make plus and minus DC.  Then to the
voltage regulators like the 7805 and 7806.  The 7805 type of regulators are
very common.  They shut down when too much current makes them too hot.
Commonly used in 1980's electronic equipment.  If the 7805 is putting out
less than 4.9 volts then something is drawing too much current.
>   I'm at work and can't continue.  Try bringing it to a local Robotics
Club meeting, or the Electronics club or students group at the local
community college.
> 
> From: xjnx0x <concken@...>
> To: vintagesynthrepair@yahoogroups.com 
> Sent: Tuesday, April 24, 2012 8:58 AM
> Subject: [vintagesynthrepair] Simmons SDE
> 
> HI, I'm new to the list.  
> 
> I have a beloved Simmons SDE that started acting flaky circa 1998.  The
SDE is a 6 voice, 4-op FM percussion synthesizer midi rack unit.  At the
time it would fail to start up when turned on, but I could coax it into
working by flipping it on and off a few times.  Eventually this didn't work
anymore and I retired it.. it sat in the corner of my studio for about 12
years... Recently I decided I missed it terribly, I opened it up and found
some blown caps in the power supply.  I replaced these and got the unit to
turn on again.  It now powers up nicely and all the functions on the front
seem to work just fine, responds to midi, responds to button presses,
responds to knob movements on the display (only through about half of their
range), but there is no sound except for an intermittent buzzing.  
> 
> I took it into a local shop on Saturday, they didn't know what it was and
they didn't want to mess with it, told me to try reloading the patches...
I'm pretty sure that's not the problem because the patches are at least half
unchangeable presets which I assume would be stored in ROM.. If this thing
is to live again, its is up to me to raise it from the dead.  I can't find
schematics for it anywhere.  
> 
> So I looked up the Yamaha FM chips... The datasheet says they need 5v,
minimum 4.8v, but I measured the voltage between pin 1 and 21 and they are
only getting 4.5v.  
> 
> Because of this, I'm suspecting the PS has more problems that need to be
addressed and I think that's the place to start.  I'm hoping, fingers
crossed, that the PS going out and me flipping it on and off like a dumbass,
didn't fry any of the output circuitry.
> 
> There are 3 ICs in the PS, a 7805, a 7806, and another one I can't
remember off the top of my head right now (88xx something?) but it has the
same package as the two voltage regulators.  All three of these were at one
time bonded to a little aluminum tray inside the case for a heat sink.  I
don't remember if there were still bonded when I opened it up, but they are
not bonded now as I had to remove the board to replace the caps.  I've tried
to make sure they are in contact with the aluminium whenever I power it up
but I don't have thermal contact paste and they and the transformer coil do
get pretty hot.  The datasheet says the 7805 can't deliver as much current
when its not heat sink-ed (heat sunk??) I'd assume this is the case for the
others as well.  
> 
> So, how should I go about troubleshooting the PS circuit, without a
schematic or even knowledge of what the voltages are supposed to be?  Any
suggestions for dissipating the heat with something temporary? (I'm sure it
will be taken apart a few more times before its fixed.)  Anything I should
watch out for?  Could the ICs not being in thermal contact have hurt them?
Could the PS going bad have damaged other parts of the machine?  
> 
> I have some experience soldering and building things, but don't mess with
power supplies much because frankly they kinda scare me.  
> 
> 
> 
> 
> 
> ------------------------------------
> 
> Yahoo! Groups Links
> 
> 
> 
>     http://docs.yahoo.com/info/terms/
>




------------------------------------

Yahoo! Groups Links

>
> Try having a look at this
> http://www.onsemi.com/pub_link/Collateral/MC7800-D.PDF it is the data sheet
> for ON semi's 78xx range may help with the pinouts, also it may be worth
> measuring the output voltages using the AC millivolt range if you have one
> on your meter as this will give you an idea of the ripple on the supply
> line, it may also be an idea to measure the input to the regulators as if
> one of the rectifier diodes or a cap has gone open circuit before the
> regulator the input voltage may not be high enough.
> 
>  
> 
> John Rose
> 
>  
> 
> (www.astrodevelopments.com)
> 
>  
> 
> From: vintagesynthrepair@yahoogroups.com
> [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Alan Probandt
> Sent: 25 April 2012 00:22
> To: vintagesynthrepair@yahoogroups.com
> Subject: Re: [vintagesynthrepair] Re: Simmons SDE
> 
>  
> 
>   
> 
> The description sounds like a linear power supply as were common for music
> gear in the mid 1980s.  In the 1990s small units (between 500 milliAmps and
> 1 Amp) began using switching power supplies.  The switchers run cooler and
> more efficiently, but are more complicated.
> 
>    Generally test power supplies under full load.  In this case with the
> rest of the unit attached.  But if the 7805 voltage is stable +5v with the
> ribbon cable disconnected then some chip or part is  pulling more current
> than it is supposed to.
> 
> If there is no sound except a buzzing, check if the buzzing is 60 or 120
> Hertz.  If so, then power supply ripple voltage from the AC mains is getting
> through to the output.   The output stage is usually an op-amp with plus and
> minus voltages.  Check if there is voltage on the power pins of the op-amp.
> Try running the chip numbers through google.  You'll get directed to the
> data sheet companies but you can also get data sheets for older parts from
> the manufacturer web sites.
> 
>   If nothing works, try selling it on eBay.  People there do pay real money
> for broken equipment.
> 
>  
> 
> From: xjnx0x <concken@...>
> To: vintagesynthrepair@yahoogroups.com 
> Sent: Tuesday, April 24, 2012 1:13 PM
> Subject: [vintagesynthrepair] Re: Simmons SDE
> 
> 
> Thanks for your reply, to clarify the power supply is 120V input and is
> built into the unit on its own little PC board with little plastic offset
> clips, inside an aluminum sub-chassis which also contains the transformer.
> I can also see plenty of large diodes on the board which are probably part
> of the bridge rectifier.  
> 
> My idea for the next course of action tonight was testing the input and
> output legs of each of the ICs to see what they're delivering.  Should this
> be done with the rest of the unit connected via the ribbon cable, or
> disconnected?  Will the presence/absence of the rest of the unit affect the
> operation of the power supply?  
> 
> thanks for your help.  I'll look into an electronics club... good idea.  
> 
> Christian
> 
> --- In vintagesynthrepair@yahoogroups.com, Alan Probandt <alan_probandt@>
> wrote:
> >
> > First off, there's several types of power supplies.  The type that plugs
> into the wall and converts 120VAC (220vac in UK and Europe) to, generally,
> +5VDC and +12/-12VDC regulated. Versus those that have a transformer
> wall-wart that plugs into the wall and delivers between 9 and 15 Volts AC to
> the unit.  If you have the 120VAC version (there's a wall plug coming from
> the Simmons) then trace out the high 120VAC paths on the power supply
> circuit board.  Don't touch these copper lines with your fingers with the
> power on.
> >    The high voltage usually goes to a small internal transformer to be
> converted to about 12 volts AC.  Then some diodes, bridge rectifiers, and
> high value electrolytic capacitors to make plus and minus DC.  Then to the
> voltage regulators like the 7805 and 7806.  The 7805 type of regulators are
> very common.  They shut down when too much current makes them too hot.
> Commonly used in 1980's electronic equipment.  If the 7805 is putting out
> less than 4.9 volts then something is drawing too much current.
> >   I'm at work and can't continue.  Try bringing it to a local Robotics
> Club meeting, or the Electronics club or students group at the local
> community college.
> > 
> > From: xjnx0x <concken@>
> > To: vintagesynthrepair@yahoogroups.com 
> > Sent: Tuesday, April 24, 2012 8:58 AM
> > Subject: [vintagesynthrepair] Simmons SDE
> > 
> > HI, I'm new to the list.  
> > 
> > I have a beloved Simmons SDE that started acting flaky circa 1998.  The
> SDE is a 6 voice, 4-op FM percussion synthesizer midi rack unit.  At the
> time it would fail to start up when turned on, but I could coax it into
> working by flipping it on and off a few times.  Eventually this didn't work
> anymore and I retired it.. it sat in the corner of my studio for about 12
> years... Recently I decided I missed it terribly, I opened it up and found
> some blown caps in the power supply.  I replaced these and got the unit to
> turn on again.  It now powers up nicely and all the functions on the front
> seem to work just fine, responds to midi, responds to button presses,
> responds to knob movements on the display (only through about half of their
> range), but there is no sound except for an intermittent buzzing.  
> > 
> > I took it into a local shop on Saturday, they didn't know what it was and
> they didn't want to mess with it, told me to try reloading the patches...
> I'm pretty sure that's not the problem because the patches are at least half
> unchangeable presets which I assume would be stored in ROM.. If this thing
> is to live again, its is up to me to raise it from the dead.  I can't find
> schematics for it anywhere.  
> > 
> > So I looked up the Yamaha FM chips... The datasheet says they need 5v,
> minimum 4.8v, but I measured the voltage between pin 1 and 21 and they are
> only getting 4.5v.  
> > 
> > Because of this, I'm suspecting the PS has more problems that need to be
> addressed and I think that's the place to start.  I'm hoping, fingers
> crossed, that the PS going out and me flipping it on and off like a dumbass,
> didn't fry any of the output circuitry.
> > 
> > There are 3 ICs in the PS, a 7805, a 7806, and another one I can't
> remember off the top of my head right now (88xx something?) but it has the
> same package as the two voltage regulators.  All three of these were at one
> time bonded to a little aluminum tray inside the case for a heat sink.  I
> don't remember if there were still bonded when I opened it up, but they are
> not bonded now as I had to remove the board to replace the caps.  I've tried
> to make sure they are in contact with the aluminium whenever I power it up
> but I don't have thermal contact paste and they and the transformer coil do
> get pretty hot.  The datasheet says the 7805 can't deliver as much current
> when its not heat sink-ed (heat sunk??) I'd assume this is the case for the
> others as well.  
> > 
> > So, how should I go about troubleshooting the PS circuit, without a
> schematic or even knowledge of what the voltages are supposed to be?  Any
> suggestions for dissipating the heat with something temporary? (I'm sure it
> will be taken apart a few more times before its fixed.)  Anything I should
> watch out for?  Could the ICs not being in thermal contact have hurt them?
> Could the PS going bad have damaged other parts of the machine?  
> > 
> > I have some experience soldering and building things, but don't mess with
> power supplies much because frankly they kinda scare me.  
> > 
> > 
> > 
> > 
> > 
> > ------------------------------------
> > 
> > Yahoo! Groups Links
> > 
> > 
> > 
> >     http://docs.yahoo.com/info/terms/
> >
> 
> 
> 
> 
> ------------------------------------
> 
> Yahoo! Groups Links
>

>
> HI, I'm new to the list.  
> 
> I have a beloved Simmons SDE that started acting flaky circa 1998.  The SDE is a 6 voice, 4-op FM percussion synthesizer midi rack unit.  At the time it would fail to start up when turned on, but I could coax it into working by flipping it on and off a few times.  Eventually this didn't work anymore and I retired it.. it sat in the corner of my studio for about 12 years... Recently I decided I missed it terribly, I opened it up and found some blown caps in the power supply.  I replaced these and got the unit to turn on again.  It now powers up nicely and all the functions on the front seem to work just fine, responds to midi, responds to button presses, responds to knob movements on the display (only through about half of their range), but there is no sound except for an intermittent buzzing.  
> 
> I took it into a local shop on Saturday, they didn't know what it was and they didn't want to mess with it, told me to try reloading the patches... I'm pretty sure that's not the problem because the patches are at least half unchangeable presets which I assume would be stored in ROM.. If this thing is to live again, its is up to me to raise it from the dead.  I can't find schematics for it anywhere.  
> 
> So I looked up the Yamaha FM chips... The datasheet says they need 5v, minimum 4.8v, but I measured the voltage between pin 1 and 21 and they are only getting 4.5v.  
> 
> Because of this, I'm suspecting the PS has more problems that need to be addressed and I think that's the place to start.  I'm hoping, fingers crossed, that the PS going out and me flipping it on and off like a dumbass, didn't fry any of the output circuitry.
> 
> There are 3 ICs in the PS, a 7805, a 7806, and another one I can't remember off the top of my head right now (88xx something?) but it has the same package as the two voltage regulators.  All three of these were at one time bonded to a little aluminum tray inside the case for a heat sink.  I don't remember if there were still bonded when I opened it up, but they are not bonded now as I had to remove the board to replace the caps.  I've tried to make sure they are in contact with the aluminium whenever I power it up but I don't have thermal contact paste and they and the transformer coil do get pretty hot.  The datasheet says the 7805 can't deliver as much current when its not heat sink-ed (heat sunk??) I'd assume this is the case for the others as well.  
> 
> So, how should I go about troubleshooting the PS circuit, without a schematic or even knowledge of what the voltages are supposed to be?  Any suggestions for dissipating the heat with something temporary? (I'm sure it will be taken apart a few more times before its fixed.)  Anything I should watch out for?  Could the ICs not being in thermal contact have hurt them?  Could the PS going bad have damaged other parts of the machine?  
> 
> I have some experience soldering and building things, but don't mess with power supplies much because frankly they kinda scare me.
>

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Christian Oncken
Sent: 30 April 2012 05:35
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Re: Simmons SDE

 

  

Hi Alan, 

 

I found a jumper on the PS board that the carries the 5v to the ribbon cable
header.  I unsoldered this instead to avoid clipping the IC lead...

 

The DVM measured 0.465A... good call on using the other DVM input, I would
have missed that.

 

I should mention again that the front panel digital functions of the box
seem to work fine, the CPU seems intact and working properly.. the buttons,
display, lights and knobs all work like they should, its just that it
doesn't make the right noises... The only thing a little strange about the
controls is that the knobs seem to only respond to about half of their
travel, their range in restricted from full left to about 12 or 1 o'clock,
after that they're full on... they are digitally encoded.  

 

So I replaced the jumper and fired it up again.  Now the encoders seem to
only work on the rights side of their travel, full right to about 12 oclock,
then they digitally "stick" at 12 even as you turn them the rest of the way
to the left.. 

 

As far as heat goes, I'm trying to not stick my fingers in there, but I
touched a wet q tip to the 3 PS ICs... the 7805 is very hot, sizzles the
water.. the other 2 are not.  The main transformer also gets pretty toasty,
(there are actually two transformers in the box.. )

 

I don't think any of the ICs on the main board get hot.  

 

Thanks again.

Christian

 

 

On Sun, Apr 29, 2012 at 4:44 PM, Alan Probandt <alan_probandt@...>
wrote:

  

The 7805 output is low but not low enough that the system shouldn't work.
It may be drawing too much current on the +5Volt.   Got a soldering iron, a
pair is small diagonal cutters, and a multimeter that measures up to two
Amps of current?  Yes, then cut the +5 volt pin on the 7805, bend legs in
different directions, attach the ammeter to the different legs (check if you
have to put the DMM probe into a different hole) and measure the current at
4.85 volts.  My guess that a good system will be between 300 and 800
milliAmps. That's normal for a microprocessor-based 'light' synthesizer of
the mid 1980s.  Are any of the ICs physically hotter than the others?

----- Original Message -----

From: Christian Oncken

To: vintagesynthrepair@yahoogroups.com

Sent: Friday, May 04, 2012 8:56 PM

Subject: Re: [vintagesynthrepair] Re: Simmons SDE

So I swapped out the 7805 and things are a little better, but different.

First of all, I can actually hear the FM generators functioning now in response to midi signals. They are very faint and buried under lots of noise but they are there.

Unfortunately, the knobs seemed to have stopped responding.. the front panel buttons work as before, but the knobs don't seem to affect the lights and display in the way they did before and have no effect on the sounds. Before I could turn the knobs in certain modes and see the display change along with them, but no longer.

The new 7805 also gets very hot, though I'm not sure if its as hot as the first one.

One strange thing I found... The 8535 (7906 equivalent) will throw sparks from the metal tab when its pushed into contact with the sub-chassis/heat sink. Any idea what could be causing this? Is the metal tab on these voltage regulator supposed to be connected to the chassis ground, because I don't believe they were connected before...

On Mon, Apr 30, 2012 at 6:46 AM, John Rose <johnhenryrose@...> wrote:

I would be inclined to change the 7805 as there are a quite a cheap component as this is where the voltage is low, if you use the 1A version as per the datasheet it should be fine, any electronics shop should have these, I would also consider picking up a tube of heat transfer compound (the ordinary white stuff would be fine) to put the regulators back against the heatsink as they will appreciate this.

John Rose

(www.astrodevelopments.com)

From: vintagesynthrepair@yahoogroups.com [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Christian Oncken
Sent: 30 April 2012 05:35
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Re: Simmons SDE

Hi Alan,

I found a jumper on the PS board that the carries the 5v to the ribbon cable header. I unsoldered this instead to avoid clipping the IC lead...

The DVM measured 0.465A... good call on using the other DVM input, I would have missed that.

I should mention again that the front panel digital functions of the box seem to work fine, the CPU seems intact and working properly.. the buttons, display, lights and knobs all work like they should, its just that it doesn't make the right noises... The only thing a little strange about the controls is that the knobs seem to only respond to about half of their travel, their range in restricted from full left to about 12 or 1 o'clock, after that they're full on... they are digitally encoded.

So I replaced the jumper and fired it up again. Now the encoders seem to only work on the rights side of their travel, full right to about 12 oclock, then they digitally "stick" at 12 even as you turn them the rest of the way to the left..

As far as heat goes, I'm trying to not stick my fingers in there, but I touched a wet q tip to the 3 PS ICs... the 7805 is very hot, sizzles the water.. the other 2 are not. The main transformer also gets pretty toasty, (there are actually two transformers in the box.. )

;

I don't think any of the ICs on the main board get hot.

Thanks again.

Christian

On Sun, Apr 29, 2012 at 4:44 PM, Alan Probandt <alan_probandt@...> wrote:

The 7805 output is low but not low enough that the system shouldn't work. It may be drawing too much current on the +5Volt. Got a soldering iron, a pair is small diagonal cutters, and a multimeter that measures up to two Amps of current? Yes, then cut the +5 volt pin on the 7805, bend legs in different directions, attach the ammeter to the different legs (check if you have to put the DMM probe into a different hole) and measure the current at 4.85 volts. My guess that a good system will be between 300 and 800 milliAmps. That's normal for a microprocessor-based 'light' synthesizer of the mid 1980s. Are any of the ICs physically hotter than the others?

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Christian Oncken
Sent: 04 May 2012 8:56
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Re: Simmons SDE

 

  

So I swapped out the 7805 and things are a little better, but different.  

 

First of all, I can actually hear the FM generators functioning now in
response to midi signals.  They are very faint and buried under lots of
noise but they are there. 

 

Unfortunately, the knobs seemed to have stopped responding.. the front panel
buttons work as before, but the knobs don't seem to affect the lights and
display in the way they did before and have no effect on the sounds.  Before
I could turn the knobs in certain modes and see the display change along
with them, but no longer.  

 

The new 7805 also gets very hot, though I'm not sure if its as hot as the
first one.  

 

One strange thing I found... The 8535 (7906 equivalent) will throw sparks
from the metal tab when its pushed into contact with the sub-chassis/heat
sink.  Any idea what could be causing this?  Is the metal tab on these
voltage regulator supposed to be connected to the chassis ground, because I
don't believe they were connected before... 

 

 

 

 

 

On Mon, Apr 30, 2012 at 6:46 AM, John Rose <johnhenryrose@...>
wrote:

  

I would be inclined to change the 7805 as there are a quite a cheap
component as this is where the voltage is low, if you use the 1A version as
per the datasheet it should be fine, any electronics shop should have these,
I would also consider picking up a tube of heat transfer compound (the
ordinary white stuff would be fine) to put the regulators back against the
heatsink as they will appreciate this.

 

John Rose

 

(www.astrodevelopments.com)

 

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Christian Oncken
Sent: 30 April 2012 05:35
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Re: Simmons SDE

 

  

Hi Alan, 

 

I found a jumper on the PS board that the carries the 5v to the ribbon cable
header.  I unsoldered this instead to avoid clipping the IC lead...

 

The DVM measured 0.465A... good call on using the other DVM input, I would
have missed that.

 

I should mention again that the front panel digital functions of the box
seem to work fine, the CPU seems intact and working properly.. the buttons,
display, lights and knobs all work like they should, its just that it
doesn't make the right noises... The only thing a little strange about the
controls is that the knobs seem to only respond to about half of their
travel, their range in restricted from full left to about 12 or 1 o'clock,
after that they're full on... they are digitally encoded.  

 

So I replaced the jumper and fired it up again.  Now the encoders seem to
only work on the rights side of their travel, full right to about 12 oclock,
then they digitally "stick" at 12 even as you turn them the rest of the way
to the left.. 

 

As far as heat goes, I'm trying to not stick my fingers in there, but I
touched a wet q tip to the 3 PS ICs... the 7805 is very hot, sizzles the
water.. the other 2 are not.  The main transformer also gets pretty toasty,
(there are actually two transformers in the box.. )

 

I don't think any of the ICs on the main board get hot.  

 

Thanks again.

Christian

 

 

On Sun, Apr 29, 2012 at 4:44 PM, Alan Probandt <alan_probandt@...>
wrote:

  

The 7805 output is low but not low enough that the system shouldn't work.
It may be drawing too much current on the +5Volt.   Got a soldering iron, a
pair is small diagonal cutters, and a multimeter that measures up to two
Amps of current?  Yes, then cut the +5 volt pin on the 7805, bend legs in
different directions, attach the ammeter to the different legs (check if you
have to put the DMM probe into a different hole) and measure the current at
4.85 volts.  My guess that a good system will be between 300 and 800
milliAmps. That's normal for a microprocessor-based 'light' synthesizer of
the mid 1980s.  Are any of the ICs physically hotter than the others?

----- Original Message -----

From: Hugh Vartanian

To: vintagesynthrepair@yahoogroups.com

Sent: Monday, May 07, 2012 1:33 PM

Subject: RE: [vintagesynthrepair] Re: Simmons SDE

Hi, I'm pretty sure 78xx pos regulators have pin 2, the tab, grounded. In-gnd-out. The 79xx neg regulators have output on the tab, iirc. Datasheets easy to find, national.com, etc.
Hugh

----- Original Message -----

From: Christian Oncken

To: vintagesynthrepair@yahoogroups.com

Sent: Monday, May 07, 2012 2:50 PM

Subject: Re: [vintagesynthrepair] Re: Simmons SDE

very strange.. I'm pretty sure the ICs were not insulated from the heat sink when I opened it up. So either they weren't in thermal contact with it with a very small gap, the heat sink compound acted as an insulator, or there were little insulators in there that slipped out when I took it apart.

So I measured the power supply outputs again with the power supply disconnected and found 16v on what I'm pretty sure is supposed to be the 6v output leg of the 7806. I swapped the 7806 out for a new one and the voltages were the same. Any idea what could be causing this?

Thanks

Christian

----- Original Message -----

From: jammie

To: vintagesynthrepair@yahoogroups.com

Sent: Monday, May 07, 2012 3:57 PM

Subject: Re: [vintagesynthrepair] Re: Simmons SDE

they are a thin square strip for the back of the power regulator

and a small thermal plastic washer with an internal raising that sits inside the hole of the power reg

theres a hole in this for a 3mm screw the hole in the reg is 4mm

so the rased 4mm insert on the 5mm washer fits the 4mm regulator hole the 3mm screw fits throught the 3mm hole so that there is a 1mm insulation gap from the reg then the thermal strip wich is about 0.5mm thick sits behind the regulator against the heat sink or chassis this insulates the reg from chassis you then clamp it up tight to get good thermal contact

your measureing the input the input can be upto 18v depending on the psu transformer used if a 240 to 36vac secondary is used

then it goes through a bridge rectifier circuit which makes it dc with the filter caps for ripple then this unregulated supply goes to the power regs which regulate the supply

read the service manual it will tell you the exceptable voltage for input and output and the ripple percentage allowed before service

----- Original Message -----

From: Christian Oncken

To: vintagesynthrepair@yahoogroups.com

Sent: Monday, May 07, 2012 2:50 PM

Subject: Re: [vintagesynthrepair] Re: Simmons SDE

very strange.. I'm pretty sure the ICs were not insulated from the heat sink when I opened it up. So either they weren't in thermal contact with it with a very small gap, the heat sink compound acted as an insulator, or there were little insulators in there that slipped out when I took it apart.

So I measured the power supply outputs again with the power supply disconnected and found 16v on what I'm pretty sure is supposed to be the 6v output leg of the 7806. I swapped the 7806 out for a new one and the voltages were the same. Any idea what could be causing this?

Thanks

Christian

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Christian Oncken
Sent: 09 May 2012 14:41
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Simmons SDE

 

  

So it turns out, looking around for info on those ICs, the 7805 and
7806 parts have the the metal tab connected to ground, the 7906 has it
connected to -6v... Its strange because I don't remember removing any
insulators from it when I disassembled it. I remember the parts being
stuck to the heatsink with some sort of glue, but that was a long time
ago so I might be mistaken.

Jammie, specifically I'm measuring the wire on the ribbon cable that
goes to the rest of the synth that I've traced back to the output leg
of the 7806. If should be +6v but its more like 16v. Unfortunately I
am unable to find a service manual or schematics for this box.

So the next thing I'm thinking is the caps. There are a total of 6
caps in the PS, three 2200 uF 16v electrolytics... these were
obviously blown out when I opened it up and I replaced them. They
connect the input legs of the ICs to ground. There are also 3 dipped
tantalum caps connecting the output legs to ground, the value is hard
to read because they're pretty close in there with the other parts..
I'll bend some things around and look closer tonight.

I'm not sure quite how to test the caps. Looking for shorts with my
DMM and testing them in circuit with the power off, the large
electrolytics give me a steadily rising resistance in one direction
only. The tantalums seem to have resistances of 5k, 7k, and 10k.

Hugh, I really appreciate the invite. I'm in Saint Louis, MO. I'll
try to take some pics but I'm not sure how good my cellphone is at
taking macro shots.

Thank you all.
Christian

----- Original Message -----

From: Christian Oncken

To: vintagesynthrepair@yahoogroups.com

Sent: Wednesday, May 09, 2012 2:41 PM

Subject: [vintagesynthrepair] Re: Simmons SDE

So it turns out, looking around for info on those ICs, the 7805 and
7806 parts have the the metal tab connected to ground, the 7906 has it
connected to -6v... Its strange because I don't remember removing any
insulators from it when I disassembled it. I remember the parts being
stuck to the heatsink with some sort of glue, but that was a long time
ago so I might be mistaken.

Jammie, specifically I'm measuring the wire on the ribbon cable that
goes to the rest of the synth that I've traced back to the output leg
of the 7806. If should be +6v but its more like 16v. Unfortunately I
am unable to find a service manual or schematics for this box.

So the next thing I'm thinking is the caps. There are a total of 6
caps in the PS, three 2200 uF 16v electrolytics... these were
obviously blown out when I opened it up and I replaced them. They
connect the input legs of the ICs to ground. There are also 3 dipped
tantalum caps connecting the output legs to ground, the value is hard
to read because they're pretty close in there with the other parts..
I'll bend some things around and look closer tonight.

I'm not sure quite how to test the caps. Looking for shorts with my
DMM and testing them in circuit with the power off, the large
electrolytics give me a steadily rising resistance in one direction
only. The tantalums seem to have resistances of 5k, 7k, and 10k.

Hugh, I really appreciate the invite. I'm in Saint Louis, MO. I'll
try to take some pics but I'm not sure how good my cellphone is at
taking macro shots.

Thank you all.
Christian

----- Original Message -----

From: Christian Oncken

To: vintagesynthrepair@yahoogroups.com

Sent: Monday, May 14, 2012 4:17 PM

Subject: Re: [vintagesynthrepair] Re: Simmons SDE

I got the SDE working Saturday morning. The 16v on the output of the 6v regulator was caused by the trace for its ground connection breaking off. The traces on this board were very delicate, I had to rebuild 3 of them. I also replaced the 3 tantalum caps just to be safe.

Thankfully, the problem in the power supply did not cause any other apparent faults in the rest of the machine. The regulators and the transformer don't get very hot now either.

It works perfectly and is just as quirky and strange as I remember 10 years ago. I've since lost one of the screws for the rack ears, and a red plastic panel that goes over the display... there also seems to be an acoustically audible buzzing sound (the box itself makes a noise) that appeared after the machine was left on for a few hours. Is this a cause for concern?

Next up on the bench I have a Korg Poly Six with a bad voice, but I'll give you all a break from me for a month or so...

Thank you all for your help.

Christian

----- Original Message -----

From: Christian Oncken

To: vintagesynthrepair@yahoogroups.com

Sent: Monday, May 14, 2012 4:17 PM

Subject: Re: [vintagesynthrepair] Re: Simmons SDE

;

I got the SDE working Saturday morning. The 16v on the output of the 6v regulator was caused by the trace for its ground connection breaking off. The traces on this board were very delicate, I had to rebuild 3 of them. I also replaced the 3 tantalum caps just to be safe.

Thankfully, the problem in the power supply did not cause any other apparent faults in the rest of the machine. The regulators and the transformer don't get very hot now either.

It works perfectly and is just as quirky and strange as I remember 10 years ago. I've since lost one of the screws for the rack ears, and a red plastic panel that goes over the display... there also seems to be an acoustically audible buzzing sound (the box itself makes a noise) that appeared after the machine was left on for a few hours. Is this a cause for concern?

Next up on the bench I have a Korg Poly Six with a bad voice, but I'll give you all a break from me for a month or so...

Thank you all for your help.

Christian