[sdiy] TR-909 FS.. $300.. U Fix

Jim Johnson jamos at technotoys.com
Mon Jun 10 19:34:45 CEST 2002

Well, I give up. 

I have a TR-909  that has ONE problem.. I got it cheap, discovered the
problem, and have tried to fix it to no avail.. so now I'll sell it for
what I have into it.

The problem is this: the "crack" portion of the snare sound is gone.
Occasionally it will return, but only once in a great long while.

I've isolated it to a single chunk of circuitry: the transistor that
provides the trigger to the VCO and envelope circuits. The collector of Q40
- one of two transistors that buffer the trigger from the digital circuits
- remains at 15 v, regardless of the input to the trigger conditioner.

I've replaced this tranny with a piece suggested by the guy at the local
electronics store - a NTE290A in place of the specified 2SA1115-F - but no
joy. I'm suspicious of that replacement.. but even more so, I'm suspicious
of my trouble shooting ability, and I'm a little sick of this. 

Cosmetically this is a 9 out of 10 - a couple of minor scrapes - and all
other electronics are in perfect shape. The thing spent some time on the
bench of a local amp tech, but this was over his head  (he actually fixed
one other problem, a noise transistor in the ride cymbal).

If your troubleshooting skills are better than mine, this will be a good
deal. I only want to know what the problem is once you've solved it. 

$300 plus shipping, US only. Has original box and manual.

Jim Johnson 
Metaphoric Software
Makers of Techno Toys
Software for Electronic Music
info at technotoys.com

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