Vintage Synth Repair

On Sun, 17 Mar 2002, Brian Andrew Marek wrote:

> Anybody have any experience with Prophet 600 repair?  I'm working on one
> for a friend.  When you turn it on, power is supplied in the correct
> voltages to the right places, but no sound is produced and the LCD
> screen doesn't even light up.  Every once in a while when you turn it
> on, you will get a random synthesized howling from all oscillators, but
> this sound cannot be affected in any way by any of the knobs, switches
> or other controls - not even the pitch control or volume control!  I'm
> trying to see if I can cadge a Z-80 microprocessor chip off of someone I
> know, but that's pretty much pure guesswork...

  I have repaired Prophet-600s in the past.  It certainly sounds like the 
Z80 microcomputer sytem is not running.  I would suspect the program ROM 
first, then the RAM and CPU.  Entirely possible a glue logic IC failed as 
well.  What software version is the program ROM labeled?

Crow
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