Just working this little amp through. Someone worked on it before, and theres a couple things going on with it that I'm trying to sort through atm. This amp is missing R151 near C67. Both of these pieces tie into the non-bridging speaker terminals.
If the cap and missing resistor are in series and one end of the pair connects to the negative speaker terminal and the other end of the pair connects to the positive speaker terminal, it's a zobel network. The amp will work without it. There should be one for each channel.
If you can't find the fault, post the voltages on the TL494 (or whatever they're using).
IC#
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:
If you can't find the fault, post the voltages on the TL494 (or whatever they're using).
IC#
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:
It has a 494P.
IC#
Pin 1: 0.003
Pin 2: 4.85
Pin 3: 0.075
Pin 4: 0.010
Pin 5: 1.492
Pin 6: 3.662
Pin 7: 0.002
Pin 8: 12.30
Pin 9: 5.25
Pin 10: 4.86
Pin 11: 12.45
Pin 12: 12.61
Pin 13: 4.97
Pin 14: 4.97
Pin 15: 2.744
Pin 16: 2.471
The power fets check out on the DVM, but one of them appears to have been replaced and has a crack in it. Both are IRFZ44. I removed the one with a crack in it (Q48) so only Q49 remains. Q48 on the bench confirms it is messed up; but not shrted. Transformer displays a "decent looking" sqaure wave on the scope but only +/- 2.5v.
IC#
Pin 1: 0.003
Pin 2: 4.85
Pin 3: 0.075
Pin 4: 0.010
Pin 5: 1.492
Pin 6: 3.662
Pin 7: 0.002
Pin 8: 12.30
Pin 9: 5.25
Pin 10: 4.86
Pin 11: 12.45
Pin 12: 12.61
Pin 13: 4.97
Pin 14: 4.97
Pin 15: 2.744
Pin 16: 2.471
The power fets check out on the DVM, but one of them appears to have been replaced and has a crack in it. Both are IRFZ44. I removed the one with a crack in it (Q48) so only Q49 remains. Q48 on the bench confirms it is messed up; but not shrted. Transformer displays a "decent looking" sqaure wave on the scope but only +/- 2.5v.
11.92V on Q49 pin1. I took Q48 off the board so nothing.
Well, not nothing. ~3.5vDC where the Q48 should be
Well, not nothing. ~3.5vDC where the Q48 should be
The other FET(s) defective. 12v is leaking to the gate.
You should have had ~5v to the gate pad for the FET you removed. If you don't, the driver transistor has failed.
You should have had ~5v to the gate pad for the FET you removed. If you don't, the driver transistor has failed.
Two bad FETs. Got it. I have some IRZ44 spare from another rebuild and wil give them a try once I confirm 5v are on the gate w/o fets.
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