[sdiy] A little mouse 'told me'....

[Bob Weigel]

I recently purchased a Korg Delta that sounded like an easy fixer 
upper.  No signal so I figured a problem in the TOS or vco section 
right?  The guy neglected to tell me any of the obvious problems until 
after the auction!

1) busted joystick
2) missing knob
3) and then when I got it I discovered rust under the paint on the 
edges; obviously stored somewhere damp and
4) smelled mousy...

Sure enough.  I opened it up and wires were chiewed through.  At first I 
thought insulation had melted off but I looked closer after I'd blown 
the bits of insulation and mouse turds out, to find they were chewed. 

I love deltas and thought I should go ahead since some of the chips are 
fairly valuable and it appeared man of them would have survived... and 
so on to trouble shoot it after scrubbing/soaping the boards. 

Here's what we found.  To make the painful story short one thing went 
out after another.  I immediately replaced all but one op amp on the 
lower two boards as the others either fell off during cleaning or were 
obviously in such bad shape they had to be pulled.  About 40 diodes went 
by the same and half a dozen capacitors.  I noticed many caps were 
showing some sign of blistering under the jackets also and they turned 
out to be bad along with sevearal others which would cause early 
envelope decays.

But the amazing thing....and maybe this is just my usual bad luck of 
late...but one of the big divider chips was obviously rusty yet it 
worked at first and the less rusty one failed immediately.  I have a 
scrap unit and pulled chips as needed to fill the spots.  After that one 
then the middle one did die while testing.  Got it replaced and the last 
one which showed little sign of rust even failed!   D just dropped out! 
Replaced it and all is well in the synth section.  ODDLY ENOUGH.....all 
of the other chips on the ensemble board survived other than the rotted 
off op amp and 4 transistors and the aforementioned capacitors.  But 
guess what!  Great signal and modulation/clock coming into the MN3004's 
but nothing out of the outputs!  Un...freakin'....believable!   Every 
valuable chips except the TOS bit it.  Oh and there were bad poly caps 
in the vco also.  I replaced with an odd arrangement of the little 
yellow multilayer ceramcs or whatever they are for now.

Anyway...certainly the most destruction per sqare inch of circuit board 
I've ever seen.  I'm sure this mouse received a promotion and he's 
probably off infesting a Mono/Poly or Moog Opus 3 somewhere hoping for a 
shot at the big leagues.   This mouses skill level in knowing just how 
to destroy the most expensive chips has to be gaining him recognition in 
his profession today.  -Bob