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Old 2nd February 2013, 03:09 AM   #11
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YES
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Old 2nd February 2013, 04:29 AM   #12
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Does it produce clean audio with a load?
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Old 2nd February 2013, 05:25 AM   #13
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Its clean, a nice wave but a little noisy looking. I tested each side 4 ohm bridged load. Got a nice wave but a little noisy.

The channel that has the bias transistor jumped from E-C wont bias obviously.

So yes it produces audio with a load all 4 channels.
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Old 2nd February 2013, 05:33 AM   #14
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If it produces clean output to clipping, the bias transistor or one of the components in that part of the circuit would likely be the problem.
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Old 2nd February 2013, 06:47 AM   #15
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Replaced all the A06 and A56 in that channel.

Replaced the 2 outputs in that channel again.

Nothing checks open as far as testing on the board.

Same issue. This is just like the 2 800a2 I could never figure out. Same cinareo, same test to work, same everything.

If I leave the IRF9540 out of the circuit the amp powers up fine. For some reason it does not like that IRF9540 being in there, I just dont get it.
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Old 2nd February 2013, 09:41 AM   #16
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Please read #15 first.

I believe the problem may be with the IRF540 section of that channel.

The gate and source pads for the 9540 with it removed or installed both have rail voltage and none on the drain.

The 540 pads with it removed or installed only have rail on the source pad and not the gate.

Wether I remove the 540 or the 9540 the channel only produces the upper half of the waveform.
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Old 2nd February 2013, 02:38 PM   #17
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If it produces clean output up to clipping with a load and doesn't draw excessive current with the jumper in place, that would tend to indicate that ALL of the components in the channel were OK with the exception of the ones for the bias circuit. Carefully check all of the components in the red rectangle for the defective channel.
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Old 2nd February 2013, 07:59 PM   #18
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Everything in the bias circuit was completely fine in and out of circuit. All tested within tolerance.

But..........after careful review of the board under magnification I found 2 things wrong.

R122 10k.......Someone had a 1k resistor in its place.
D102 1N5226B was leaky.

I replaced the 5226 with a 4728 same voltage just a 1/2 watt higher its the closest I had on hand. Do you think it will be a problem?

After replacing R122 with a new 10k resistor and D102 the amp powers up and is stable with no pulsing and produces clean audio into clipping.
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Old 2nd February 2013, 08:10 PM   #19
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The diode won't be a problem.
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Old 2nd February 2013, 08:29 PM   #20
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Why would R122 having a 1K vs a 10K resistor cause this problem?
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