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Old 22nd March 2009, 01:20 AM   #21
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that was from pin 1-3 , black on pin 3
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Old 22nd March 2009, 01:42 AM   #22
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With that much voltage on the gates, the amp should be drawing excessive current. Far too much current to have 52v on the output.

This is the left channel. You stated that you had 52v on the right channel. Is that channel blown also.
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Old 22nd March 2009, 02:26 AM   #23
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The whole time it was the left channel that was bad, sorry for the confusion.
It quit having dc on the output for a few minutes but it was crackling and popping through the speaker.

When I measure with the black probe on the neg power terminal and and the neg speaker terminal I get -52v .

When I check pins 2-3 on the left channel i get 104 volts
on the right channel pins 2-3 have 52 volts.

I am getting between 4 to 10 volts on pins 1-3 now.
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Old 22nd March 2009, 02:29 AM   #24
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Did you replace the 0.1 ohm source resistors?
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Old 22nd March 2009, 01:24 PM   #25
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I only replaced the ones that were bad.
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Old 22nd March 2009, 02:35 PM   #26
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If you have 14v from pins 1-3, you should have ~0v from 2-3. If you don't, you have defective outputs.

If you have ~0v from 2-3 (with 14v from 1-3 on both the IRF640s and IRF9640s), you should have excessive voltage across the 0.1 ohm resistors (which should either burn them out or cause the amp to draw excessive current).

You should have replaced all of the 0.1 ohm resistors in this channel for better long term reliability.
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Old 22nd March 2009, 03:18 PM   #27
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If that is the case than why on the channel that is working is there 2.243 volts between pins 1-3 and 52 volts between pins 2-3? ( is this what the other side should be like also to be working properly?)

I have + and - rail voltage on right channel , but on left I only have - and it is reading 104 volts.
The amp is drawing alot of current keeps shutting power supply down .
This amp might be to much of pita for me to fix.
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Old 22nd March 2009, 03:37 PM   #28
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At 2.5v, the output FETs are not quite driven on. They won't begin to conduct to somewhere around 3.3v. At more than 4v, the transistors (in the defective channel) should be fully on. If both the 640s and 9640s are on, it's like taking a piece of wire and shorting the rails together (actually like shorting them to ground in this amp). Are you 100% sure that all of the 0.1 ohm resistors are at 0.1 ohms?

This amp doesn't work like a normal amplifier. It drives the output by dragging the rail voltage towards ground. When there is a fault, this can cause you to have 2x the actual rail voltage on one set of outputs while the other outputs have no rail voltage. As it is, the amp should be drawing excessive current. We need to determine why it is not. I suspect that you still have open 0.1 ohm resistors.

You also need to determine why Q216 had only 2.6v while the rest had 14v (1-3). I suspect an open gate resistor.

What is the current rating of the supply?
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Old 22nd March 2009, 04:15 PM   #29
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q216 is no longer among the living , it popped and I clipped it from the circuit after it fried an emitter

My supply is rated at 10 amps.

The 640's have around 8 volts on pins 1-3 and 0volts on pins 2-3

The 9640's have about 11 volts on pins 1-3 and 104 volts on pins 2-3

Checked emitters and all are 0.1
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Old 22nd March 2009, 04:29 PM   #30
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If you have negative 11 volts from pin 1-3 (black probe on 3) on the 9640s and 100+v from 2-3, the 9640s have failed.
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