R738 getting hot suggests high frequency oscillation.
I asked if the outputs were originals or replacements.
I asked if the outputs were originals or replacements.
I believe they are original. I have not gotten in there yet to see any numbers.
I noticed another oddity. On the main board right channel Q707 is different then Q708 on the left board. 707 is E2730 708 is M25 27722.
Q701 & Q702 also are all M25 27722
None of these match the Schematic. I do not know enough about Transistor values to know if this matters. Just one more difference on Left channel.
Im hoping later today to do some testing values of component on board. Put the board back and check some voltages.
I also see pin 25 is lower then the rest on the mount. Going to correct that.
Thanks
Sorry. I deleted that part of the post because it was not reproduced in more testing.
i was referring to the bias trim pots R715 & 716
So Far working only the left channel, yesterday i replaced Q702 with two matching hfe PNP KSA992FTA as well as c702 on suspicion.
Also cleaned both Bias pots with D5 which I do not think helped as the right side seems to not do much anymore.
Results were Left speaker output now has steady 30+volts on it. Bias pot changes not.
The right side has near 3MV on output
checking output drivers Q1,2,&4 all have around half a vote, across base/Emitter bias voltage.
Q3, which was the hot transistor has 0 volts across BE. Either Q710 or Q 708 is not switching on the bias... or Q3, it is shorted. Next step to me is removing leads from B/E of Q3 and look for short? Or retest all voltages and make good notes.
Bias voltage between TP01 &TP02 is close to matching TP 03 & 04 so I think my differential amp replacement was a success.
Looking for the easy route here.
Please jump in.
Also cleaned both Bias pots with D5 which I do not think helped as the right side seems to not do much anymore.
Results were Left speaker output now has steady 30+volts on it. Bias pot changes not.
The right side has near 3MV on output
checking output drivers Q1,2,&4 all have around half a vote, across base/Emitter bias voltage.
Q3, which was the hot transistor has 0 volts across BE. Either Q710 or Q 708 is not switching on the bias... or Q3, it is shorted. Next step to me is removing leads from B/E of Q3 and look for short? Or retest all voltages and make good notes.
Bias voltage between TP01 &TP02 is close to matching TP 03 & 04 so I think my differential amp replacement was a success.
Looking for the easy route here.
Please jump in.
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I don't think they were proprietary they just have HK part numbers on them. Probably all RCAs since the whole design is supposedly pretty much out of the RCA transistor manual. The ones with heatsinks attached may be 40409 and 40410, although there were several like that.
Craig
Craig
The BLUE capacitor near connector 25/26 looks to have a bulging top on it.
If it is, it must be replaced.
A new one must be installed with the proper polarity.
Replace it on both channels with a 220Uf , 35V lytic.
The two transistors at the Q702 location should be touching each other, with a dab of heatsink grease between them, and a zip tie holding them together.
That way, they will track each other better thermally.
If it is, it must be replaced.
A new one must be installed with the proper polarity.
Replace it on both channels with a 220Uf , 35V lytic.
The two transistors at the Q702 location should be touching each other, with a dab of heatsink grease between them, and a zip tie holding them together.
That way, they will track each other better thermally.
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