Vintage Synth Repair

Maybe there are some Ozzies here, I'm not so far - in Japan, just  
behind the corner and then to the left.

I' still fight with repairs of my Yammies - SY1 (some problem with  
filter block), CS15D needs setting and tuning, one CS40m after  
recapping doesn't work, another CS40m - PSU after recapping has some  
problem with -15 V rail...

I'm sure I will have some questions later... how to solve it.

No holiday here, this word is not in my dictionary :-)

Daniel Forro


On 12 Aug, 2013, at 3:47 PM, eidorian@... wrote:

> Hi Hugh,
>
> Thanks for your email and sorry for the slow response.  I've been  
> doing
> too much other non-electronics stuff lately :-(
>
> At the moment the +15V rail is measuring ~ +17V and the -15V rail
> "exponentially" rises from ~ -12V or so to ~ +0.8V when power is  
> applied
> then stays there  (it gets to 0V in about 3-5 seconds, then slowly
> creeps up to +0.8V over the next 30 seconds or so).  The 1K resistor  
> in
> the +15V circuit is very hot to touch.  I've replaced or tested OK
> pretty-much every component on the board now.
>
> I agree that there is probably just one common problem causing the
> issues with both the +15V and -15V rails.  Next step I think is trying
> to isolate what's causing the 1K resistor to carry all the current
> rather than it flowing through the darlington transistor circuit  
> like it
> should.  I'm hoping once that's fixed the +15V will self-heal due to
> some unusual condition being removed.  Sorry if that sounds vague but
> I'm not in front of the schematic at the moment!
>
> Also I'm about to go on holidays for two weeks in a couple of days'
> time, so unfortunately it'll be a while before I get back to this one.
>
> I'm in Australia, so a long way from most people :-)
>
> Cheers,
> A.