My FG504 had suddenly died when I tried to use it yesterday (no output basically). After a lot of probing around I discovered that Q270 on the A3 Loop board had failed. It's specified as 151-0438-00, a selected SPS2927. I'm sure this one has come up before but I can't find a spec or alternative device.... can anyone suggest a suitable device please. I've put in a BC212L just to prove the fault diagnosis but it would be nice to get the right part.
In the course of trouble-shooting I wasn't sure where to start. The manual describes the complete workings but doesn't say how/where the triangle waveform actually starts off in life! I eventually realised the whole thing was a closed loop (A3 LOOP Board should have been a clue :-)), which doesn't help diagnosis..... had to go probing all transistor terminals looking for trouble. Can anyone explain the signal generation process in a simple fashion?
