Hey everyone! I’m having an issue with a Roland SH1000 synth. It turns on but it’s not making any sound. I can hear an extremely quite high pitched note when I press a key and crank my amp all the way up. I’ve checked the voltages in the supply and I’m getting the correct ones. I’ve noticed that when I trace the signal with a scope there’s a sine wave that I can trace all the way to the output jack, but the second I plug in a cable the sine wave disappears. I also noticed that when I try to listen to the sine wave with an audio tracer, the sine wave disappears when I clip the ground lead on. I’m pretty perplexed by this and any help would be appreciated, thank you!
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Make sure your scope is grounded to an analog ground in the circuit, like ground side of an easily accessible resistor or cap. Sometimes chassis or other metal on a synth won’t provide a good enough ground (especially on older synths) so your scope input will act as an antenna and you’ll pick up the mains voltage as a 50 or 60 Hz sine wave on your scope. Be careful not to clip the scope ground to the side of a component that isn’t grounded because that creates a short circuit to ground that can damage the synth or scope.
If you’re still seeing a sine wave despite having the scope grounded then let me know.
Sorry for the late reply! I went back in and grounded my scope (usually don’t need to) and I traced the signal to the input of the VCF and it’s extremely quiet. When I unplug the input connector and scope the oscillator at the connector it’s a healthy signal, but when I plug the connector back in the signal is practically gone. I also measured the voltages on “Pack 2” on the VCF board and there is .037vdc on pin 2 where there should be 15v. Any idea why that voltage would be missing?
Problem solved. on the PL board, a 100 ohm resistor (I believe R288, hard to read) next to C247 was burned up and shorting the +15v. Replacing this resistor brought back power and now the synth works!