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Old 8th December 2012, 03:38 AM   #11
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Perry,

i seem to have ~110v on the drain and source for 10 of the outputs and ~8v on the remaining. Any ideas come to mind. should i remove the outputs that have the lower voltage readings and start working my way back.
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Old 8th December 2012, 03:47 AM   #12
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What is the DC voltage across the speaker terminals?
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Old 8th December 2012, 04:21 AM   #13
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i have 0.5 volts. I have some sound but it is distorting. I think there is an open transistor or diode somewhere. Don't think it is a shorted one or i would be seeing some other issues.
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Old 8th December 2012, 04:30 AM   #14
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If you don't have any significant DC, it sounds like it's in protect mode. Is the protect LED lit?

If not, measure the DC voltage across it to see if it's open.
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Old 8th December 2012, 05:57 PM   #15
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the protect light has a faint bit of light but it only can be seen with the lights off. I don't think it is in protect mode because if i hook my scope probe to pin 7 on U304 it sends the amp into protect mode and the led fully lights up as long as the probe is touching.
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Old 8th December 2012, 07:03 PM   #16
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Confirm that you have a good triangle waveform on pin 7 of U303 and that it has essentially no DC offset.
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Old 9th December 2012, 05:51 PM   #17
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perry,

i measured the voltage across the protect LED and got 0.532V and a nice triangle waveform output B pin 7 with no baseline offset with max peak of 2.12v
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Old 9th December 2012, 08:12 PM   #18
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Perry,

I removed Q401 for troubleshooting the driver circuit for that bank of outputs and powered the circuit. unfortunately i didn't have my current limiting resistor installed and blew that bank of outputs. Can i remove the blown bank and power the amp to troubleshoot the bank that is not powering up
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Old 10th December 2012, 02:36 AM   #19
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The current limiting resistor in the B+ line would not have saved the FETs. There is too much secondary capacitance. When working on these amps, the only protection that I've found is either adding fuses or resistors in the red and blue wires.

You shouldn't power up any FET circuit with any of the driver components out of the circuit unless you know the circuit well enough to know that the FETs will be held 'off' when power is applied.
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Old 10th December 2012, 04:25 AM   #20
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Perry,

should both banks of FETS be powered at 110 v or do they alternate? I noticed that T400 and T401 are both hooked to U202 and U204 which have a toggle A and B for the input. could one of the secondary output be open on t400 pin2, 3?
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