Rhodes Chroma Polaris

Thanks for the information Paul,
i will check this out these days as far as i can
and hope to be lucky.

cheers Harald


> 
> Yes, it's pretty easy. If you can't find a 2SA1029, any small PNP transistor
> should work, like a 2N3906, as long as you figure out which leads are which.
> However, since answering you, I realize there are other failures that could
> cause the same problem, but they should be easy to check.
> 
> First, open the unit up and unplug the three-wire cable that runs from the
> output board and plugs into the main board, which has an 8-position
> connector at the end. If the volume remains high, then the problem is on the
> output board, probably the transistor. If the volume drops to zero, then
> there is a problem in the sample-and-hold circuit that drives the master
> voltage control line.
> 
> This line comes from Z603-8, one of the op-amps in the fifth channel. (The
> service manual is available at rhodeschroma.com.) You'd have to remove the
> keyboard to get at this, but that's only a few screws. Fortunately, these
> parts are socketed, so you could tell if the op-amp is bad by swapping the
> part with the analogous part in a different channel, say, Z503. If that
> fixes it, you're all done, because that op-amp section isn't used for
> anything in the other channels. If not, then it's probably one of the CMOS
> switches in the sample-and-hold circuit, which would be either Z601 or Z602.
> Again, you could swap those with, say, Z501 and Z502, and if everything
> works, you're done. This would mean that only that op-amp in Z603, or that
> particular switch channel in Z601 or Z602, had burned out.
> 
> Ideally, you would diagnose these things by reading voltages with a meter
> while moving the master volume slider. If the above doesn't fix it, then
> you'd have to delve deeper and do a real diagnosis. Not every electronic
> failure can be solved by swapping a few socketed parts. But you might get
> lucky.
> 
> -- 
> 
> Ciao,               Paul D. DeRocco
> Paul                mailto:pderocco@...
>