When first powered on there is a bit of a sweeping sound that goes up and down for a few seconds and then the sound of the patches is initially garbled sounding (like it’s being modulated by noise or something). After about 10-30 seconds it clears up and the thing behaves normally from that point on.
Any speculation on what this is? Is it a dying capacitor or something?
unstable power supply The capacitors in the power supply are failing. Too much variability will eventually fry the chips inside. There could also be other failure issues the power supply is trying to compensating for.
Thanks for your reply. Do you think it may have anything to do with the fact that this has the SQ80-M modification? I have not seen anyone reporting that it stresses the power supply or anything, but at the same time there is not an abundance of literature on the mod.
I have no info on it. this requires opening the unit and investigating.
Well I replaced all the large capacitors on the power supply board (there are two 10uF and one 22uF capacitors that I’ve yet to replace) with no change in behavior. I did figure out that it takes about a minute to go to normal behavior from power on, but if I turn it off and back on again fairly soon, it only takes a couple of seconds for it to be normal. If I leave it for a couple minutes and turn it back on it takes slightly longer. I also noticed that on a new start-up (after a long time off) the patches change around by themselves at first and eventually settle down shortly before the sound becomes normal.
I think you’d want to check voltages on the power voltage regulators too, and make sure any heat sinks (if any) are attached normally.
If you have data backed up, have you tried the factory reset yet?
That timing variation with quick power cycling you mention, IMHO suggests the charging/discharging state of capacitors.
Apparently it was bad cap(s) at the output amplifier (U26). According to the guy who repaired it, these are commonly bad or initially of a value that isn’t really ideal but were maybe used as a cost-saving measure? Not sure. Anyway, so far it seems much better. I also think the main chips (stacked ones for the mod) may have not been seated properly, because when I first got it back from repair, it was still doing some slightly weird things but I made sure that was firmly in place and now it hasn’t been giving me any trouble.