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Yamaha M2 re-cap, partial rebuilt, or just play dilemma

raycarr00

raycarr00

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purchased a mint, "non working", unmolested, very heavy, m2 (built 1979? 40 years! )that had blown fuses (no info. on incident) and burnt display lights. After slowly powering it up with a dim bulb tester and variac, it appears to work just fine(on dim bulb tester and variac), except bias and dc offset wouldn't set.
Currently replacing trim pots and capacitors.
What if something else like a transistor is leaking, defective, thus affecting the setting of bias and dc offset and which might have caused fusses to blow(bias setting?)?
Question: should I just recap, play(and wait for whatever to fail, act up); or replace transistors, power resistors, fusistors and diodes with substitutes?
Typically, I would pull all transistors and compare to datasheet info. using a Chinese "do it all" tester; but it's time consuming, the boards are not part numbered per the schematic ("color by number")and I'm afraid something might get damaged (a trace)or mixed up.
So far, diodes and resistors seem to check out on one disassembled channel using a dmm and without pulling them. 3 resistors parallel to each other and by a transistor 2sa(TR301 or4)814 darkened the board a bit, apparently due to overheating, but check out as good. advice, comments, appreciated.
 
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raycarr00 said:
purchased a mint, "non working", unmolested, very heavy, m2 (built 1979? 40 years! )that had blown fuses (no info. on incident) and burnt display lights. After slowly powering it up with a dim bulb tester and variac, it appears to work just fine(on dim bulb tester and variac), except bias and dc offset wouldn't set.
Click to expand...
Are you getting a relay "click" shortly after power on?
 
Bias and dc offset done per hifiengine schematic. dimbulb tester may have affected results. I haven't powered it up since Aug 26, 2016, when we discussed trimmers. I don't recall hearing the usual relay click sound at the time, just that it powered up and sounded fine for several hours and until I decided to replace the trimmer pots to try to correct the issue with the bias and offset current not staying set. I'll finish replacing the trimmers and the one capacitor left on the one channel, and slowly power it up again. I'll then try powering it up without the variac and dim bulb tester. I'll need to order the 2 remaining 22K 1/2 watt trimmers; this is what I've managed to find, so far: 3386P-1-223LF. For the 1k's I do have in hand, 3309w-102-nd bourns, bent them backwards because of the pin orientation( like dick the bruiser would do an opponent). Noting that the pot may respond in a backward fashion. I also have the 1k trimmers in the 3386P version; use them instead? comments ideas
 
Use the dim bulb the first time you power it up after putting it back together.Just to make sure nothing is shorted.
 
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