So I just got my 2nd unit and have recapped it. I replaced all outputs, all caps, most diodes thoroughly checked all diodes on amp boards. No shorts anywhere or bad solder joints.
I seem to have an issue with the left channel. I get 5 volts dc on the output, the right channel is perfect. I traced it back to the amp board by disconnecting the speaker outs that connect from the amp board to the relay board. Both channels biased with no problems. I can adjust the DC offset on the bad channel but it certainly doesn't go low enough to eliminate the volts of DC. The pre-drivers have not been changed due to them all testing fine. The weird thing is when I got the amp the right channel had blown outputs and that channel is perfect now after the refurb. Any pointers or places to start?
I seem to have an issue with the left channel. I get 5 volts dc on the output, the right channel is perfect. I traced it back to the amp board by disconnecting the speaker outs that connect from the amp board to the relay board. Both channels biased with no problems. I can adjust the DC offset on the bad channel but it certainly doesn't go low enough to eliminate the volts of DC. The pre-drivers have not been changed due to them all testing fine. The weird thing is when I got the amp the right channel had blown outputs and that channel is perfect now after the refurb. Any pointers or places to start?
Check voltages on +ve and -ve power rails, ie pins 18 (+52Vdc) and 21 (-52Vdc)
Measure voltages on each side of R501 and repeat for R503. Measure resistance
or R501, R503, R517, R518 (amp powered off/unplugged).
Testing the easy cases first like unbalanced supply or one of the resistors drifting
out of spec before hunting failed silicon.
Measure voltages on each side of R501 and repeat for R503. Measure resistance
or R501, R503, R517, R518 (amp powered off/unplugged).
Testing the easy cases first like unbalanced supply or one of the resistors drifting
out of spec before hunting failed silicon.
Rails check out. Haven't measured voltages across 501 503 yet but ohms reads the same on both channels. I have been comparing resistances from the good channel with the bad and haven't come across any discrepancys except for on the bad channel the diodes measure 10k accross vs the good channel measures about 1k ( a resistor going open maby?) I pulled the diodes agian to check and confirmed they are good as well as 517 and 518 and they are good.
Fixed! A 10 ohm resistor by the DC pot was open which took out the 100uf cap by it. I noticed one of the caps I changed had a slight buldge to it and sure enough the 100uf was reading 80uf. Biased and offset adjustments are perfect! I'll throw up some pics of the restoration if anyones interested.
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