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Old 1st October 2012, 06:39 PM   #21
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Sorry, miscounted the pins. Pin 14 stays at 3.9V for a few seconds and then starts pulsing between 3.3V and 3.9V. After that the process repeats.
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Old 1st October 2012, 09:15 PM   #22
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Are there any transistors connected to pin 14? If so, remove it. Does that allow the amp to idle normally?
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Old 2nd October 2012, 12:14 PM   #23
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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?
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Old 2nd October 2012, 04:15 PM   #24
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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.
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Old 2nd October 2012, 10:04 PM   #25
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Remove whichever transistor you removed to make the amp power up previously. Does the amp still draw excessive current with the rectifiers in and the outputs out of the amp?

Are you sure that the rectifiers are in the correct locations?
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Old 3rd October 2012, 07:58 AM   #26
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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.
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Old 3rd October 2012, 08:06 AM   #27
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Is either rectifier shorted?

With the rectifiers out of the circuit, what's the resistance from the center rectifier pads to the outer pads?
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Old 3rd October 2012, 08:20 AM   #28
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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
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Old 3rd October 2012, 08:28 AM   #29
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With the rectifiers out of the circuit, what's the resistance from the center rectifier pads to the outer pads?
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Old 3rd October 2012, 08:55 AM   #30
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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.
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