[sdiy] Crumar DS2 Problem

[WeAreAs1 at aol.com]

In a message dated 8/21/04 11:33:30 AM, elfenjunge at gmx.net writes:

<< so i'm gettingt 
some new IC's for the adsr board as well, since its only a few bucks 
more on my order list an all ic's in the synth have sockets ;) >>

All the IC's are in sockets???  OK, that's useful information.  Hey, before 
you rush out and buy a bunch of parts, why don't you try removing the existing 
parts from each socket and carefully cleaning their pins, as well as cleaning 
the sockets themselves?  A very common failure for instruments of that vintage 
(late 70's to mid 80's) is parts not making good contact in sockets, usually 
due to oxide buildup on the IC pins.  Ask anyone who has repaired a lot of 
Oberheim OBx and OBxa and/or Prophet V synths.  When I deal with this, I will 
first make sure that I'm properly grounded with an antistatic wrist strap, then I 
take out the chips and gently scrape both sides of the pins with an Xacto 
knife.  You will immediately see the difference -- the metal of the pins, which 
before was dull and gray, will now be nice and shiny.  I also apply just a tiny 
amount of Cramolin onto the socket itself, then I work the IC in and out of 
the socket a few times to let the IC's pins kind of scrape/clean the 
wiper/receptacles of the sockets (this is all done with the synth's power turned OFF, of 
course).  This should also be done with the pins and sockets of any and all 
multipin connector cables that are found in the instrument.  Really, try this 
before you throw a bunch of new parts in there.  It's far more likely that you 
have a bad contact somewhere than you having an actual bad chip, and if you 
wait to do it until after you start replacing chips, then you have to deal with 
the question of whether the new chips are actually good (yes, that can be a 
real concern).

As a synth repair tech with over 25 years of professional experience, I would 
estimate that greater than 75% of all electronic repair problems are 
electromechanical in nature, and not a result of bad electronic components.  I'm 
talking about things like oxide on IC pins, cracked or "cold" solder joints, broken 
wires, bent pins, dirty switches and pots, etc..   This is especially true 
these days in the era of surface-mount, oven-soldered components.  Remember that 
next time your new digital fizzbang virtual modeling synth goes belly-up -- 
It's probably not a bad 144-pin DSP chip, it's the crappy factory soldering job 
they did on that chip, or another one somewhere on the main board.  Believe 
me, there's something very satisfying about reviving a dead Nord Lead or Yamaha 
FS1R with just a soldering iron and some liquid solder flux (and a steady 
hand...).

People are always so eager to replace good components when they try to repair 
their own synths.  Folks, IC's and transistors are not like brake pads or car 
tires.  In a properly designed system, they don't wear out from normal use, 
and they don't (usually) simply fail after 20 years of faithful service.  I am 
actually more leery of new parts, because unlike the old parts that have been 
happily humming away for years, they don't have a *history of reliability*.  
Think about that for a minute.  Unless logic and all evidence points you 
directly to a bad chip, always suspect something else first -- something less sexy, 
something mechanical in nature.  

This is not to say that IC's and semi's never go bad.  They do, but far less 
often than most people think (and passive components go bad even LESS often).  
Often, the less experienced tech will try replacing an IC and be fooled into 
thinking that the IC was bad simply because the act of taking the old IC out 
of the socket and putting in the new one created enough scraping action to 
clean the oxide off the socket and fix the real problem.  What he doesn't realize 
is that the next time the synth gets moved, or played, or goes through some 
kind of temperature change, that new IC may move again in the socket, just ever 
so slightly, but enough to make the problem come back.  Murphy cheerfully 
reminds us that this is most likely to happen onstage at your next very important 
gig, probably right in the middle of your big showstopping synth solo, once 
again redefining the word "showstopping".

Michael Bacich