Vintage Synth Repair

If it were me and I know nothing about this synth by the way...I'd
start by looking at the PSU with a scope....then assuming this is
perfect I'd be looking around the CPU to see what activity I have
going on again with a scope or logic probe referring back to the
schematics, reset lines..clock, ports etc etc. I'd then check the
circuit around the rom and ram etc..chip selects etc etc write enable
blah blah..theres so much it could be..you only need one dead node in
the logic circuit and the whole thing won't work.
  
I'd say the rom is ok if you still have a problem with the test rom..

I don't see any benefit in bypassing the digital side even if it were
possible..what with the garbage on the screen there is quite clearly a
  logic problem. 

Phil.




--- In vintagesynthrepair@yahoogroups.com, "Brendan Haley"
<b.haley@...> wrote:
>
> Is there anyone out there that has experience troubleshooting
problems with the Prophet 600, specifically the digital side of things?
> 
> I have a broken Prophet 600 that powers up. I get no sound out of
it, and "gibberish" on the numerical readout. With the standard eprom
in it it doesn't even really respond in any discernable way to
pressing any of the keypad numbers.
> 
> I have the diagnostic eprom from Wine Country, which also does not
act as expected although with the Diagnositc chip in the keypad does
produce reproducable results, or in other words, the "gibberish"
changes in a systematic way when I press the membrane keypads.
> 
> So I am assuming that whatever is wrong with this is mostly on the
digital side (I think....). Of course, I am not so good with digital
stuff (though I do have a logic probe, and a scope, etc.)
> 
> Any thoughts, or anyone out there willing to give me some hints, or
maybe tell me some more directed things to try?
> 
> Also, is there any way to kind of "bypass" the digital side, to just
get a sense that the "analog" side is working properly (I see the
waveforms I think I should see on the appropriate pins on the
Oscillator chips so I THINK they are good....
> 
> -brendan
>