I recently picked up a Concertmate MG-1 for $20. When I plugged it in it made a lot of noise it obviously wasn’t supposed to. A lot of white noise and things like that. You can barely hear the actual sound it’s supposed to make way under all of the white noise. I left it for a few hours and came back to try to diagnose it and when I plugged it back in, it smoked and now it won’t power up. Considering it’s old there are loads of things that it could be, but I figured I would see if anybody knew what it might be before I start going through it.
Hello and welcome.
If real smoke actually came off it, who knows all that could have been damaged…
The obvious would be that the transformer might have shorted out, burned, and blown a fuse.
The only way to find out would be to open it up and look for traces of burns.
Now, as to why it made a lot of noises the first time you powered it up, that could be a lot of things, too.
From scratchy white noise pot, to defective mixer section, to defective parts, you name it.
My take on it…TIFWIW.
When I think smoke, I think capacitors. Then I think resistors. Resistors are easy to spot. They are discolored, and often times the circuit board under them is charred. Usually resistors blow after something else does, so if you find a bad resistor, follow the path to the nearest components on the trace.
Drastic noise as you described could have been an op amp that then gave up and shorted out. I’ve seen them get hot enough internally when this happens to blow out a piece of the DIP case and emit a puff of smoke. Tek Tip: The smell is distinctive and with practice you can smell the difference between semi-conductor smoke (integrated circuits or transistors - maybe diodes), toasted resistor smoke or shorted / leaky capacitors. Overheated electrolytic caps smell different than tantalum caps. Whenever possible, observe these smells and make a mental note about their source and character. These observations might save some time and help direct the search in future trouble shooting tasks.
A visual inspection might reveal the source of the smoke but not necessarily. If it no longer powers up then you have a power supply that shut down due to blown fuse(s), a regulated voltage in current limit due to heavy load, or a component failure. It is sometimes necessary to isolate the supply from the load and test the supply separate from the rest of the circuitry.