PLAN B analog blog

All,

We have discovered a very odd problem with leaky caps on three Model 10's.  They make 
audible noise by themselves (faint clicking sound) at the end of each cycle.  It's impossible 
to hear this unless you make your unit self-oscillate and hol the thing up to your ear.  
Tat's when its the most pronounced.  Even then, if it's mounted in a rack it's still ard to 
hear.  You have to basically power it up out of the racktand hold you ear to it while it's 
running.

The problem stems from a leaky .47 cap and our records indicate we only purchased 6 of 
these caps.  I've found three units with this problem, one form the feild, two in my own 
synth. So there may be three others out there somewhere.

If you discover yours does this, you have two options:

1)  Send it to us, we will replace the cap and returnit  free of charge

2)  Replace it yourself.  Here's how:

The single .47 uf cap on this EG is in the integrator.  It's located about mid board, right 
above an LM3900 IC.  By above I mean closer to the faceplate.  The specific type of cap is 
round, about the thickness and diameter of a dime (US currency) and light brown/mustard 
colored.  NOT ALL OF THESE PARTS WE'VE SHIPPED HAVE THIS PROBLEM - ONLY THE SIX 
FROM THIS SPECIFIC LOT. Further, not all the M10s shipped had this type of disk cap at 
this location.  Sometimes we use a smaller dipped part, or a molded ceramic cap made by 
WIMA (a little red plastic square). We have verified from the manufacturer that they had 
one bad lot that they are aware of. So if yours has one of these mustard-colored, dime-
sized caps, don't panic - it won't break over time.  Just give it the 'ear' test to determine if 
you hear the faint clicking when the M10 is oscillating.  It's best to turn the A/D and Time 
Domain knobs fully CCW so that the unit oscillates in the audio range. It's a go/no go type 
thing.  It either does it or not and won't start doing it later.  

We've also used these on the Model 13's and there has been no problem - actually in the 
specific applicationin the M13 it would never manifest.  

If yours exhibits this problem, just replace the .47 with another one.  They are a garden-
variety component, what we call int he business a 2-AM part (meaning ou could find one 
for sale at 2 AM) - they are everywhwre.  You probably have 30 of the in your kitchen 
applicances (don't pull your coffee maker apart for this!).   There is no specific type of cap 
which will work better than others - AS LONG AS IT'S NOT POLARIZED - so electrolytc caps 
(the metal can types which are also on this board (10uf)) or tantiluma (tear drop shaped 
dipped parts with a + indicator on the side)  should NOT be used.

Make sure the power is off when you replace the part!

Contact me off line if you'd like to arrange a return or if you have further questions on this 
simple repair.

thanks for your time,

- P