Vintage Synth Repair

Sorry it took so long to get back on this, I was gigging & ingnored my mail for a 
week or so. Ok, here goes...I checked back on the SEMs  (about 6) I've fixed 
that had this problem-sure enough, one required both A23 & A24 replaced for 
NO modulation.The other SEM had 2/3 to near-full  modulation and looking 
closely at my notes for the client I saw I had indicated A24 as the cause.
of that issue due to "liquid ingress"-The client had spilt a pint of best 
Guinness**  as I recall, so the A24 issue does indeed look like a bit of a red 
herring for  our friend Bakis !  Ahh... must update my memory-chip!!
Thanks Mike!

Regards,

Mantridcat



**-Not the strangest by any means....I've had a Farfisa Compact organ that 
kept detuning intermittantly-the cause was a live caterpillar pupating between 
the pillars of the main tuning-choke!!
The 're-housing' of a small family of mice I found living happily in a Hammond 
A101 is a story for another day......



--- In vintagesynthrepair@yahoogroups.com, WeAreAs1@a... wrote:
> 
> In a message dated 8/15/05 1:05:33 AM, "mantridcat" <mantridcat@y...> 
> writes:
> 
> << Another likely cause is A24 -This is an LM741 common or garden op-
amp and 
> I have had this cause no or full modulation when it goes belly-up. >>
> 
> Hello Mandricat,
> 
> Thanks for your help and experience on the subject.  Nevertheless, I can't 
> readily see how a failing A24 could cause full modulation.  It could definitely 
> cause no modulation, or could cause a huge static pitch offset if its output 
> went high or low, but how could it increase modulation, if there is no 
> modulation signal placed at its input?  Have you really seen this before as a 
failure 
> mode?  If so, what am I missing?
> 
> Mike B.