problem w/ a prophet 600

[Paul Maddox]

Tom,

>Its a digitally controlled analog synth, and some times the digital control
>stops working. I can still play it, I just cant change the sounds. 
>Sometimes
>it will start working again if I play with the knobs or turn it off and on,
>but other times, i just gotta give up for the day.

Hmmm, sounds bad... heat problem?

>This problem used to happen every once I a while but now its like every 
>day.
>I have a theory it could be heat related, but i'm not sure. I realy wouldnt
>even know how to test for that. My worst fear is that its the rom going.
>I'm and EE student and i got and Oscope and a bunch of other toys avalibe,
>but i dont know where to start looking.

ahh, heat problem...

Ok first thing I would do is open up the case, solder a couple of wires on 
to crucial points and monitor them... the supply rails, +/- and +5v (if it 
has one), monitor these when its working and when it fails.. if the supply 
to 5v keeps "ducking" then you may have a PSU fault, this may cause the uP 
to crash.

CHeck for dry joints, I know its obvious but this synth must be getting on, 
and I bet its been bounced around a bit, take out the circuit board and 
check them... if nesacery do ALL the joints around the digital section..

Check the output on the uP, stick your scope on a couple of the output pins 
when its working, when it dies, do it again, see if its still sending data, 
if not, the uP has locked/crashd for some reason.

Just a few thoughts

Paul


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