Vintage Synth Repair

--- In vintagesynthrepair@yahoogroups.com, "sputnik979"
<sputnik979@...> wrote:
>
> Hello guys,
> 
> I have been offered a cs20m but the owner is not sure whether 
> everything's fine with it. My question is; what are the most common 
> problems with this model I should be aware of? What about the memory? 
> If the patches are lost, does it mean that the battery has leaked and 
> destroyed the circuits? Or maybe non-corrosive batteries were used in 
> CS ?
> 
> cheers
> aero
>


I have two CS-20M's at the moment.  One working and one was until a
MUX blew up right as I was demo'ing it to a guy w/cash in hand!!  In
portland..so I had to haul it back home :-).  ANyone who believes in
'luck'..needs to really evaluate my life. hehe.

But anyway common problems:

#1 failure of tantalum capacitors which can burst and short power
supply rail(s).  Replace all those that are direct coupled to power
supply first off when repairing one of these.

#2 On my first one I fixed an op amp went south in the regulation or
had a bad contact or something...and overvoltaged everything.  By the
time the caps blew several chips had been damaged.  3 VCA's, 2 op
amps, and a partridge sound coming out of a filter or something like
that :-) hehe.  Anyway this may not be second most common problem but
it's the most damaging one and of course..happened to me on my first one.

#3 After repairing the last one and testing a while, it was working
great but then a 10 channel MUX chip blew out.  All mix and filter
settings went to maximum.  SO the stored patches still worked.  The
'manual' mode did not at that point and I have talked to yamaha who
actually still has some of those chips left!  I got two of them on the
way to have a spare.  Since the alternative is take a 16ch mux and
build a daughter board I guess.

Oddly enough..I can't remember anything about the battery in these.
I'll...pull that one open and look soon enough.  But I recall that
they were ok and not leaking. -bob