Vintage Synth Repair

The schematics are here.

http://www.korganalogue.net/korgms/service/ms20/m20s.html#3

(This looks like its the early MS-20 version with the Korg-35 
filter.  I think the later version with the 13600 OTA filter is 
somewhere on the web too.)

The keyboard circuit looks pretty straight forward.  Most of the 
connections use normalled jacks.   Are you sure that the jacks 
aren't oxidized? 

-Larry



--- In vintagesynthrepair@yahoogroups.com, Royalston <royalston@...> 
wrote:
>
> Hi
> Im new to this group...
> Ive got an MS-20 which was working fine when i bought it,  but 
has  
> recently had a few functions fail on me. I was hoping people 
might  
> have had similar experiences/ and or might be able to point me in 
the  
> right direction because unfortunately in Sydney, where I live, 
analog  
> synth repairers  are either hard to find, or totally untrustworthy.
> (If anyone knows a good one - let me know please!)
> 
> I'll try to give a detailed explanation of the problems:
> 
> The keyboard was working normally and has now stopped working. It  
> worked sporadically one day, then stopped all together.  I can 
still  
> still trigger the VCOs via CV/midi. When I press a key it still  
> lights the EG2 LED as well..so Im thinking all is not lost for 
the  
> keyboard. I took the synth apart and did some rudimentary 
resistance  
> checks with a multi-meter along the keyboard - it all looks fine -
  
> its when it attaches to the main circuit board that I get lost 
and  
> dont  know what to check
> 
> Also in the patching section the HPF and LPF patch points don't 
seem  
> to work anymore, along with a few other patch points....I'd love 
to  
> get this working again. The filters themselves work fine, just 
not  
> the patching. I know it worked when I bought it, and then just  
> stopped. Ive looked over the circuit board for dry solder joints 
too,  
> but I stopped there. (I didn't find any)
> 
> 
> Apart from that , the machine works well - I love it.:)
> 
> Thanks for reading this.
> Any thoughts would be greatly appreciated.
> 
> R.
>