Roland SH-2, frozen/unresponsive, no sound?

[WhinyLittleRunt]

Just looking for tips before I start probing around...

I just got an SH-2 and it was a bit wonky but working more or less. (It was supposed to be working perfectly). It was dumb stuff like the keyboard contacts etc. But when I opened it up I found that one of the power supply caps had completely shorted and soldered-in fuse was bad. Not even sure how it was working but it was... anyway I recapped the supply, replaced the fuse, pulled and cleaned the bus bars in the keyboard. Took my measurements, got my 30v +/- and 15v +/- where I needed them, looked good, fired it up. Worked well. Everything seemed sorted.

I fired it up earlier this evening and let it warm up. When I came back to it it was frozen, unresponsive, the rate LED was solid and no sound. Ok, so I took it to the bench and checked the power supply again - and again, looks good. Still fires up unresponsive. I did not re-cap the rest of the synth nor did I make any changes at the main boards. Any ideas?



[url=https://flic.kr/p/2fBtvYu]
[url=https://flic.kr/p/TypuFE]

[Mooger5]

Hi,
See if the envelope follower was engaged.
See if the synth responds to external cv.
See if ext audio passes through.
Where exactly are you reading 30v +/- ?

[WhinyLittleRunt]

I was getting +/- 30v at the power regulators, B and E pins. C would give me 15v + or - depending on which one I measured. I'd also get 15v +/- at the spots on the power supply (16, 17 and 20, 21):



It appeared fine until the next day and I left it on for a couple of hours to warm up. Worked ok the previous day, nothing changed.

Sounds like you know the SH-2 pretty well? I'll go check on the audio input and CV...

[WhinyLittleRunt]

Ok, here's what I do know now after doing a bit of probing...

No it doesn't pass audio. I haven't even tried CV yet. I found that when the power supply is disconnected from the rest of the synth, I get my 14-15v as expected. When I connect it (3 different cables), the power draw is different, and I wind up with -10v (as low as 7 or 8v). So I started unplugging the connectors one at a time and I got to the second one on the 052H176 PCB (OPH62) and powered it on with 15v, and a functional rate LED. So, it's definitely something on that board somehow drawing the power or shorted I'd think, right?

[WhinyLittleRunt]

I fixed it...

Turned out to be a shorted IC (TL082), IC18. Found it with the touch test; ouch! Also changed out the caps in that board while it was out.

[Mooger5]

Well done. The ''touch-o-meter'' and the ''smell-o-meter'' are very valuable diagnoseing tools. The latter isn't so effective, but it's safer.