This had a mind- blowing fault. At start up, the display should come up with the name and version of the unit, and then it should tell you the setting that exists for the fx section. This one came up with all that, and then ‘left channel amp overheating’, which would display once or twice and then revert to the correct readout. If this were the only problem it would have been tolerable. Unfortunately, it would, sometimes, give the error readout again and hang on it. The thermal error would, after a timeout period, shut the lot down. Hard to ignore that, if you happen to be in the middle of a show.
There is a transistor mounted on each heatsink that senses the temperature (its a BC550 if I remember right) and sends the signal back, eventually to the microprocessor on the display pcb. I say eventually, because it calls in at just about every pcb in the thing before it actually gets there. This is bad news, because it has to travel a lot of ribbon cable and pcb tracks before it gets to the microprocessor which is a variation on the 40 pin 80C range.
To cut a long story short (and it was a long story) it was the 80C that was at fault. That should be easy. It’s plugged into a 40 pin socket, you can still get 80C chips…..but…….this is an eprom programmable chip, and it has been programmed for this machine. And you ain’t going to get another.
There are two things you could do, unless you’re going to either dump it, or use the power amp section. In which case you just unplug all the ribbon cables from the top preamp/mixer section, and use the aux inputs at the back. You could disable the temperature readout by cutting the 12th and 13th cables in the 16 way ribbon cable into the display pcb. But then you don’t know if it might be overheating. Or you could disable the shutdown outputs, so it won’t shut down if it does overheat. Neither of these alternatives is wonderful, but if you can put up with it, you’ve still got a functioning powered mixer.
These Studiomaster mixers (which have completely nothing to do with the current Chinese gear) were high quality, largely hand-made units pruduced in the u.k. They’re well worth the effort of keeping them running, wherever it’s possible; in my view.