Vintage Synth Repair

There are 6 electrolytic capacitors on the Moog Prodigy circuit board. And as I understand the schematics, 4 of them are in the audio circuit. And after 30+ years, I assume their performance is compromised. And since it *seems* to me that the sound of the synth has been slightly changed over the last time, I’m thinking to replace all electrolytic capacitors, using the same capacitance/voltage replacements, of course.

The question is, do the capacitors affect the actual sonic characteristics of the output signal? At least, in a case with Moog Prodigy?

My concern is that the modern capacitors (different series, different characteristics) will make the sound different. And I would like to keep the "original" coloration of the sound as much as possible.

I would greatly appreciate any input..

Thank you!

Electrolytic capacitors can change their value over the years, which can alter the sound. But that's pretty rare. Electrolytics usually  have a slightly higher distortion in the audio path than better materials , which supposedly can be heard.  I've never come across any actual evidence of that,  although I suspect that there are some people who actually can  hear the di fference in a direct A/B listening test . There have been  claims that some electrolytics sound better than others, but I've never heard of  ANY support for that.


  There is one tech that I have conversed with that says he fixes all the problems in his vintage gear just by replacing the electrolytics. B ut with me and all the other techs I've conversed with, changing electrolytics almost always  makes no difference at all. There is a greater chance of really cheap electrolytics failing that decent qua li ty ones,  but Moog doesn't use cheap components. Electrolytics are said to have a life span  of a certain number of years, which is specified in parts catalogs. One example: "guaranteed lifetime of 20000 hours" (more than 2 years).  But getting back to  real life, t he oldes t piece I've worked on was a Rickenbacker amp from the 40s, and the original electrolytics in that were all just as good as   new. So I personally go by  the rule: "if it isn't broke , don't fix it".


   But on the other hand, there  DEFINITELY are some people that you can impress by telling them  you changed out all of  the electrolytics. So it really depends on what your goal is.

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




From: "gk.box@... [vintagesynthrepair]" <vintagesynthrepair@yahoogroups.com>
To: vintagesynthrepair@yahoogroups.com
Sent: Friday, July 29, 2016 3:23:21 PM
Subject: [vintagesynthrepair] Moog Prodigy: do capacitors model/type affect the sound?


 












There are 6 electrolytic capacitors on the Moog Prodigy circuit board. And as I understand the schematics, 4 of them are in the audio circuit. And after 30+ years, I assume their performance is compromised. And since it *seems* to me that the sound of the synth has been slightly changed over the last time, I’m thinking to replace all electrolytic capacitors, using the same capacitance/voltage replacements, of course.








The question is, do the capacitors affect the actual sonic characteristics of the output signal? At least, in a case with Moog Prodigy?








My concern is that the modern capacitors (different series, different characteristics) will make the sound different. And I would like to keep the "original" coloration of the sound as much as possible.








I would greatly appreciate any input..












Thank you!

I recapped my Moog prodigy a few years ago and one challenge was finding electrolytic capacitors with radial leads. Most are PCB mount these days.




On 1 Aug 2016, at 1:57 AM, Kirk Slinkard kslinkard@...<mailto:kslinkard@q.com> [vintagesynthrepair] <vintagesynthrepair@yahoogroups.com<mailto:vintagesynthrepair@yahoogroups.com>> wrote:






  Electrolytic capacitors can change their value over the years, which can alter the sound. But that's pretty rare. Electrolytics usually have a slightly higher distortion in the audio path than better materials, which supposedly can be heard. I've never come across any actual evidence of that, although I suspect that there are some people who actually can hear the difference in a direct A/B listening test. There have been claims that some electrolytics sound better than others, but I've never heard of ANY support for that.


  There is one tech that I have conversed with that says he fixes all the problems in his vintage gear just by replacing the electrolytics. But with me and all the other techs I've conversed with, changing electrolytics almost always makes no difference at all. There is a greater chance of really cheap electrolytics failing that decent quality ones, but Moog doesn't use cheap components. Electrolytics are said to have a life span of a certain number of years, which is specified in parts catalogs. One example: "guaranteed lifetime of 20000 hours" (more than 2 years). But getting back to real life, the oldest piece I've worked on was a Rickenbacker amp from the 40s, and the original electrolytics in that were all just as good as new. So I personally go by the rule: "if it isn't broke, don't fix it".


  But on the other hand, there DEFINITELY are some people that you can impress by telling them you changed out all of the electrolytics. So it really depends on what your goal is.




________________________________

From: "gk.box@...<mailto:gk.box@hotmail.com> [vintagesynthrepair]" <vintagesynthrepair@yahoogroups.com<mailto:vintagesynthrepair@yahoogroups.com>>
To: vintagesynthrepair@...m<mailto:vintagesynthrepair@yahoogroups.com>
Sent: Friday, July 29, 2016 3:23:21 PM
Subject: [vintagesynthrepair] Moog Prodigy: do capacitors model/type affect the sound?






There are 6 electrolytic capacitors on the Moog Prodigy circuit board. And as I understand the schematics, 4 of them are in the audio circuit. And after 30+ years, I assume their performance is compromised. And since it *seems* to me that the sound of the synth has been slightly changed over the last time, I'm thinking to replace all electrolytic capacitors, using the same capacitance/voltage replacements, of course.




The question is, do the capacitors affect the actual sonic characteristics of the output signal? At least, in a case with Moog Prodigy?




My concern is that the modern capacitors (different series, different characteristics) will make the sound different. And I would like to keep the "original" coloration of the sound as much as possible.




I would greatly appreciate any input..




Thank you!






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My beloved DX5 started some problems...


When I switched it on after few weeks when it was not used, this two  
problems occured, without any obvious reason, and probably not  
connected together:


--------------
Problem 1
All buttons at the left side and under the display don't work. Some of  
them have LEDs lit on. When I change Performances (right side buttons  
work), Voice bank and number buttons LEDs also change (I suppose  
according to programmed data, and because there's just factory setting  
in the memory, they changed in very regular sequential pattern, one by  
on). But I can't change them manually, they don't react.
It occurs with:
+1/Yes, -1/No
2 x 6 buttons: OP Select, OP On/Off
2 x 4 buttons: Bank A, Bank B
2 x 8 buttons under the display: Voice A 1-8, Voice B 1-8


I can enter EDIT mode but all those buttons again don't work. I can  
change only Edit of Function parameters which are selected by  
Performance buttons. Data Entry fader works and can change parameter  
values.


It's not possible to activate Diagnostics (Test) mode because buttons  
which call it don't work.


Problem 2
Instrument plays all sounds (also both sounds in Split or Dual mode)  
with long Release like when Sustain pedal is On. But it is not On. The  
same behavior occurs even with no Sustain pedal connected. When I  
connected the pedal, instrument had no reaction on its position.
--------------


I tried usual stuff - checked and reseated connectors and OS Eproms on  
the main board. It didn't help.


I try to attach to this message one page with schematics of CPC and  
some other boards. Concerning the button control I suspect some  
problem in this circuit.


(Warning! There's a mistake in the description of Push Switch 31 in  
the "LED + Push Switch Table" - it should be only "+1/Yes", not "OP  
SEL".)


Concerning those permanently sounding notes I will check if the  
Sustain pedal jack socket is OK, there's a switching contact inside  
it, maybe it doesn't work properly. It can be only mechanical problem  
(I hope so).


I'd like to ask more experienced electronic gurus here what do you  
think, which component or components would you suspect? And what can  
be reason for such problem, how it could started? Just some old and  
tired component stopped to work? I have no other explanation...


Thanks for any hint or advice.


Daniel Forro

First of all: have you changed the backup battery? 99,9% of all errors
I have enountered on DX-synths have turned out to be an (almost) flat
battery.
And then: check power supply voltages. Digital stuff usually tends to  

dislike and misbehave if the power is not correct.
After that, it is the usual suspects with connectors and the like that
you have already tried.
But check the backup battery first.






Den 3. aug.. 2016 kl. 16.11 skrev Daniel Forró danforcz@...
[vintagesynthrepair]:


> [Attachment(s) from =?ISO-8859-1?Q?Daniel_Forr=F3?=
> danforcz@... [vintagesynthrepair] included below]
> My beloved DX5 started some problems...
>
> When I switched it on after few weeks when it was not used, this two
> problems occured, without any obvious reason, and probably not
> connected together:
>
> --------------
> Problem 1
> All buttons at the left side and under the display don't work. Some of
> them have LEDs lit on. When I change Performances (right side buttons
> work), Voice bank and number buttons LEDs also change (I suppose
> according to programmed data, and because there's just factory setting
> in the memory, they changed in very regular sequential pattern, one by
> on). But I can't change them manually, they don't react.
> It occurs with:
> +1/Yes, -1/No
> 2 x 6 buttons: OP Select, OP On/Off

> 2 x 4 buttons: Bank A, Bank B
> 2 x 8 buttons under the display: Voice A 1-8, Voice B 1-8
>
> I can enter EDIT mode but all those buttons again don't work. I can
> change only Edit of Function parameters which are selected by
> Performance buttons. Data Entry fader works and can change parameter
> values.
>
> It's not possible to activate Diagnostics (Test) mode because buttons
> which call it don't work.
>
> Problem 2
> Instrument plays all sounds (also both sounds in Split or Dual mode)
> with long Release like when Sustain pedal is On. But it is not On. The
> same behavior occurs even with no Sustain pedal connected. When I
> connected the pedal, instrument had no reaction on its position.
> --------------
>
> I tried usual stuff - checked and reseated connectors and OS Eproms on
> the main board. It didn't help.
>
> I try to attach to this message one page with schematics of CPC and
> some other boards. Concerning the button control I suspect some
> problem in this circuit.
>
> (Warning! There's a mistake in the description of Push Switch 31 in
> the "LED + Push Switch Table" - it should be only "+1/Yes", not "OP
> SEL".)
>
> Concerning those permanently sounding notes I will check if the
> Sustain pedal jack socket is OK, there's a switching contact inside
> it, maybe it doesn't work properly. It can be only mechanical problem
> (I hope so).
>
> I'd like to ask more experienced electronic gurus here what do you
> think, which component or components would you suspect? And what can
> be reason for such problem, how it could started? Just some old and
> tired component stopped to work? I have no other explanation...
>
> Thanks for any hint or advice.
>
> Daniel Forro
>
>
>
>


Terje Winther

terje.winther@...
http://wintherstormer.no/

I composed and then deleted unsent a similar suggestion about the battery: my SY-99s  exhibit a bunch of random troubles when the batteries are dead and you cannot do diagnostics or resets without functioning backup batteries. It sounds like you have already reseated connectors to the panels.
  Good luck




From: Terje Winther terje.winther@... [vintagesynthrepair]

Hi, Terje,


thank you for your opinion.


This time I wouldn't suspect RAM backup battery as sound data in RAM  
are OK.


You are right concerning PSU and voltages - I will start there.


Then I will check that logic circuit which scans and convert switches.


Best regards.


Daniel Forro




On Aug 5, 2016, at 5:38 AM, Terje Winther terje.winther@... 
  [vintagesynthrepair] wrote:

>
>
> First of all: have you changed the backup battery? 99,9% of all  
> errors I have enountered on DX-synths have turned out to be an  
> (almost) flat battery.
> And then: check power supply voltages. Digital stuff usually tends  
> to dislike and misbehave if the power is not correct.
> After that, it is the usual suspects with connectors and the like  
> that you have already tried.
> But check the backup battery first.
>
>

Thank you for the advice, it seems to me that battery is OK because  
sound data in RAM are without problems. But of coarse I will measure  
the voltage.


I cannot do diagnostics only because it is started by pressing the  
buttons which don't work now...


Daniel Forro




On Aug 8, 2016, at 4:46 AM, Paul paul.krull@...  
[vintagesynthrepair] wrote:

> [Attachment(s) from Paul paul.krull@... [vintagesynthrepair]  
> included below]
>
> I composed and then deleted unsent a similar suggestion about the  
> battery: my SY-99s  exhibit a bunch of random troubles when the  
> batteries are dead and you cannot do diagnostics or resets without  
> functioning backup batteries. It sounds like you have already  
> reseated connectors to the panels.
>   Good luck