I just got an Emulator III and took it home worked fine for 20 minutes then suddenly loud crackling from the speakers it was plugged into, I turned it off and it's smells like burned plastic!
I'm terrified something got ruined, obviously I won't power it on until I just take it to a tech
thing sounded so f**k good for 20 minutes I loaded string sounds off the internal HD and it was amazing sounding.
Probably a failed capacitor in the switchmode power supply, they are getting to the point of failure by now as they are old and some of them are in positions close to heat sinks. Otherwise it could be a shorted tantalum cap, or, less likely, an op-amp with an internal short.
Synthesizer service tech since 1982. Synth parts and service, Sydney Australia.