Vintage Synth Repair

Hi everybody,
my minimoog #3271 with R.A.Moog boards strikes. In this afternoon it worked very well, but 
now, four hours later I switched it on and can not hear oscillator 1 and the other both oscs 
have a very bad scaling - they are completely out of tune. What can this be? The Synth was 
stored away for a lot of years, i woke it up last week, cleaned all switchs + key-contacts and 
after that it worked  PERFECTLY! 
Now I swapped the Oscillator board with a newer one (also an older version with seven pots) 
- that works. But I love the R.A.Moog board and will repair it. Does anybody know, which 
caps should be changed after this long time? 
Thanks for your answers
+best regards from 
a very unhappy Martin

i would just change all of them.  i had a transient problem on the arp omni and had to change out every single electrolytic for tantalum.  a daunting task but an all around great habit to get into when repairing vintage synths.  then you just wait another 20-30 years to change the new ones.  also DIP are a must when repairing vintage synths.  chip faliure can be common on Juno's and replacing the parts can be an easy swap.  plus if your not experienced a quick solder job could turn in a slow and damaging one to boot.  to much heat on the chips could cause damage and if not properly heatsinked could cause damage to other sensitive parts ie.  transistors. hope it helps



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Probably the top CA3046 has failed on the VCO board. You can swap the 2 of them to see 
if the fault changes, but BE CAREFUL: they are plugged in in opposite directions.

Your machine will sound much better if you replace all of the electrolytic capacitors. There 
is only 1 on the VCO board BTW.


--- In vintagesynthrepair@yahoogroups.com, "martinreuter" <FrauReuter@...> wrote:
>
> Hi everybody,
> my minimoog #3271 with R.A.Moog boards strikes. In this afternoon it worked very 
well, but 
> now, four hours later I switched it on and can not hear oscillator 1 and the other both 
oscs 
> have a very bad scaling - they are completely out of tune. What can this be? The Synth 
was 
> stored away for a lot of years, i woke it up last week, cleaned all switchs + key-contacts 
and 
> after that it worked  PERFECTLY! 
> Now I swapped the Oscillator board with a newer one (also an older version with seven 
pots) 
> - that works. But I love the R.A.Moog board and will repair it. Does anybody know, 
which 

> caps should be changed after this long time? 
> Thanks for your answers
> +best regards from 
> a very unhappy Martin
>

--- In vintagesynthrepair@yahoogroups.com, "thirteentech" <thirteentech@...> wrote:
>
> Probably the top CA3046 has failed on the VCO board. You can swap the 2 of them to see 

Uups.... I can only see two "3821" Chips - they are labeled "GG 3821N 7323". The other 8 
Chips seem to be all 741 OpAmps - is this right? They are looking different, two are on 
sockets, six are directly soldered. Can I swap the 3821 with brandnew 3046?
And: I found four Electrolyte Caps on my board - one 33µF, two 4,7 µF and one 2,2µF. All are 
on the left side over the left contact-row....
Board is marked "3251" with felt-marker.
Thanks + Greetings
Martin

The 3821 is similar to the CA/LM3046 NPN transistor array, and can be substituted. Both 
chips were used in the Minimoog. If you just swap the two 3821's with one another you 
can see if the fault changes, ie: the VCO fault moves, and this will let you know if one of 
the chips is faulty. As I said before, watch the orientation as one chip will be upside down.


--- In vintagesynthrepair@yahoogroups.com, "martinreuter" <FrauReuter@...> wrote:
>
> --- In vintagesynthrepair@yahoogroups.com, "thirteentech" <thirteentech@> wrote:
> >
> > Probably the top CA3046 has failed on the VCO board. You can swap the 2 of them to 
see 
> 
> Uups.... I can only see two "3821" Chips - they are labeled "GG 3821N 7323". The other 
8 
> Chips seem to be all 741 OpAmps - is this right? They are looking different, two are on 
> sockets, six are directly soldered. Can I swap the 3821 with brandnew 3046?
> And: I found four Electrolyte Caps on my board - one 33µF, two 4,7 µF and one 2,2µF. 
All are 

> on the left side over the left contact-row....
> Board is marked "3251" with felt-marker.
> Thanks + Greetings
> Martin
>

On Wednesday 02 July 2008 03:03, martinreuter wrote:
> --- In vintagesynthrepair@yahoogroups.com, "thirteentech" <thirteentech@...> 
wrote:
> > Probably the top CA3046 has failed on the VCO board. You can swap the 2
> > of them to see
>
> Uups.... I can only see two "3821" Chips - they are labeled "GG 3821N
> 7323". 

I remember "SG3821" rather than "GG",  anybody know who makes those?

And yes,  you can substitute one for the other,  they're pretty much 
equivalent.  Also CA3086 is pretty close as well.

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
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-
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M Dakin

--- In vintagesynthrepair@yahoogroups.com, "thirteentech" <thirteentech@...> wrote:
>
> Probably the top CA3046 has failed on the VCO board. You can swap the 2 of them to see 

No, i bought new chips and the problem is the same. What´s with the OpAmps 741? Shall i 
change them? Some of they have a red dot - what means this?
By the way: there are really 4 electrolyt caps on board: c10 (thats OK) and c11, c12 and c13. 
This last three should be tantalum caps, but they are not. So what - the synth worked with 
this caps.

But now i am really helpless.....is there anybody with a beautiful idea??
greetings
Martin

do as best as you can to replace all the parts on  a board you are working on with as many readily available parts as you can.  what i would look for if audio related parts, transistors, Caps Op amps,.etc I wouldn't worry about resistors that much unless you can actually see them burnt out.  
              i mean its something to do while you wait.  plus I don't understand why you wouldn't.  its old parts that could be actually frying your chips. in the end a complete over haul could take a day and under 30 buck (apart from special purpose IC's you have to find).

Thank You all!!!!
I changed the ICs + the OpAmps of the oscillator board and now it runs. 
Now i have to repair my 2nd board1 - all oscillators are working, bit it is impossible to get a 
correct scaling. I can tune all 3 but the octave-switch don�t switches octaves...seem to be 
quints or so. What the hell may this be? I will do the same pocedure: Changing all chipps and 
some caps. But if you have a concrete tip - I will thank you.
greetz
Martin