Vintage Synth Repair

Hi guys and first of all happy easter!!!

I have some free time finally so decided to check OB8 ...
It had few problems but ... 

found dead TL081, CA3080 ... kinda regular problems that i fixed easy by replacing ics

Next is 2 voices that wont go in tune!!

so Voice 6 //// VCO 2 is going crazy //// tried with another CEM 3340 ... same thing

VCO 1 and VCO 2 are getting same KEYCV.. VCO 1 track perfect ... VCO 2 is kinda playing what he wants !!
.. so .. voltages on VCO 2 are ok ... +/-5 and +/-15
IC 3340 is fully functional one

KEYCV is from same source to VCO 1 and VCO 2...

Any idea???

Thanx

Damir

Check for cold solder on the .022mfd polystyrene caps (clear axial looking caps) that are at the left side of each voice board.  I had voices that wouldn't tune and I just put new caps in there.  Problem hasn't come back.  If you put new ones in, even though polystyrene caps are bipolar they have a side that grounds better where the foil seam is.  Sometimes they aren't marked, but sometimes they are.

Good luck
Greg

--- In vintagesynthrepair@yahoogroups.com, "Damir" <roginator1@...> wrote:

>
> Hi guys and first of all happy easter!!!
> 
> I have some free time finally so decided to check OB8 ...
> It had few problems but ... 
> 
> found dead TL081, CA3080 ... kinda regular problems that i fixed easy by replacing ics
> 
> Next is 2 voices that wont go in tune!!
> 
> so Voice 6 //// VCO 2 is going crazy //// tried with another CEM 3340 ... same thing
> 
> VCO 1 and VCO 2 are getting same KEYCV.. VCO 1 track perfect ... VCO 2 is kinda playing what he wants !!
> .. so .. voltages on VCO 2 are ok ... +/-5 and +/-15
> IC 3340 is fully functional one
> 
> KEYCV is from same source to VCO 1 and VCO 2...
> 
> Any idea???
> 
> Thanx
> 
> Damir
>

Thanks guys , I have exactly the same problem ,changed all the caps except these ones.
I will try this next.

Thanks
Arnar

----- Original Message -----
Frá: "adhmzaiusz" <adhmzaiusz@...>
Til: vintagesynthrepair@yahoogroups.com
Sent: Mánudagur, 9. Apríl, 2012 04:36:26
Efni: [vintagesynthrepair] Re: Oberheim OB8 Problems....






Check for cold solder on the .022mfd polystyrene caps (clear axial looking caps) that are at the left side of each voice board. I had voices that wouldn't tune and I just put new caps in there. Problem hasn't come back. If you put new ones in, even though polystyrene caps are bipolar they have a side that grounds better where the foil seam is. Sometimes they aren't marked, but sometimes they are. 

Good luck 
Greg 

--- In vintagesynthrepair@yahoogroups.com , "Damir" <roginator1@...> wrote: 

> 
> Hi guys and first of all happy easter!!! 
> 
> I have some free time finally so decided to check OB8 ... 
> It had few problems but ... 
> 
> found dead TL081, CA3080 ... kinda regular problems that i fixed easy by replacing ics 
> 
> Next is 2 voices that wont go in tune!! 
> 
> so Voice 6 //// VCO 2 is going crazy //// tried with another CEM 3340 ... same thing 
> 
> VCO 1 and VCO 2 are getting same KEYCV.. VCO 1 track perfect ... VCO 2 is kinda playing what he wants !! 
> .. so .. voltages on VCO 2 are ok ... +/-5 and +/-15 
> IC 3340 is fully functional one 
> 
> KEYCV is from same source to VCO 1 and VCO 2... 
> 
> Any idea??? 
> 
> Thanx 
> 
> Damir 
>