Yes, pins 13, 14 and 15 connect to several 2sa1015 and 2sc1815 transistors. I removed the closest one, 2sc1815, and now the LED is green, the power supply is working. I get 3.8v at the gates of the PS mosfets, and 22kHz at the drain pins. There is no excessive current draw and nothing gets hot. The removed transistor seems to be a part of the protection circuit, because there are traces that also lead to the audio section. I removed the transistors near tl494 and checked them one by one for shorts and leakage, but they are fine. What could cause the protection circuit to do this?
Found a bad solder joint near the protection circuit, fixed it. Now the amp idles fine with the rectifiers removed. But as soon as I install them, the amp starts drawing excessive current. Checked the audio section for shorts, but there doesn't seem to be anything out of the ordinary. All output transistors are removed.
Removed the same transistor, but it doesn't change anything. When I put the rectifiers in, the amp starts to draw excessive current. The rectifier with it diodes pointing outward should be near the audio section. I also tried to briefly swap their loctions, but the excessive current draw is still there.
FMG22R
Center leg to left leg: 5.4Mohm (red probe on center, black on left)
Center leg to right leg: 5.4Mohm (red probe on center, black on right)
Probes reversed reads 0.L.
FMG22s
Left leg to center leg: 5.4Mohm (red probe on left, black on center)
Right leg to center leg: 5.4Mohm (red probe on right, black on center)
Probes reversed reads 0.L.
They don't appear to be shorted
Center leg to left leg: 5.4Mohm (red probe on center, black on left)
Center leg to right leg: 5.4Mohm (red probe on center, black on right)
Probes reversed reads 0.L.
FMG22s
Left leg to center leg: 5.4Mohm (red probe on left, black on center)
Right leg to center leg: 5.4Mohm (red probe on right, black on center)
Probes reversed reads 0.L.
They don't appear to be shorted
Left rectifier
Red probe on center, black on left: 13.2Mohm.
Red probe on center, black on right: 0.L.
Black probe on center, red on right: 8.6Mohm.
Black probe on center, red on left: 5.6Mohm.
Right rectifier
Red probe on center, black on left: 13.6Mohm.
Red probe on center, black on right: 0.L.
Black probe on center, red on right: 7.3Mohm.
Black probe on center, red on left: 5.7Mohm.
Red probe on center, black on left: 13.2Mohm.
Red probe on center, black on right: 0.L.
Black probe on center, red on right: 8.6Mohm.
Black probe on center, red on left: 5.6Mohm.
Right rectifier
Red probe on center, black on left: 13.6Mohm.
Red probe on center, black on right: 0.L.
Black probe on center, red on right: 7.3Mohm.
Black probe on center, red on left: 5.7Mohm.
Completely disconnect the amp from everything. Find the terminals for each of the rail caps. Determine which is positive and which is negative for each rail cap. Connect your 12v power supply across each rail cap. Make sure that you have the proper polarity. Do this with a current limiter or a 3-5 amp fuse in the power line. Does the amp continuously draw more than a fraction of an amp when you touch the 12v power supply to the caps?
To clarify... Nothing will be connected to the amp except the +/- of the 12v supply to the individual rail caps, one at a time.
To clarify... Nothing will be connected to the amp except the +/- of the 12v supply to the individual rail caps, one at a time.
Connected 12v power supply across each of the four rail caps, but there isn't significant current draw. They are not shorted. I have another amp for parts with a working PS, but blown audio section. Would it be possible to use its power supply and connect it to the audio section of the amp we are discussing here to see if the audio section powers up or will the protection cuircuit disable it?
That's unlikely unless the output transistors are FETs but they would have to be in the circuit and unless I'm mistaken, you stated that the outputs were out of the amp.
Connect it to the power supply through a current limiting resistor, clamp all power transistors to the heatsink and see what gets hot.
Connect it to the power supply through a current limiting resistor, clamp all power transistors to the heatsink and see what gets hot.
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