'how' should have been 'hot'.
Set the bias pot fully counter-clockwise before you apply power to the amp (after replacing any defective components).
You can't check the transistors with power on the circuit. You can't test them definitively unless you remove them from the circuit.
Set the bias pot fully counter-clockwise before you apply power to the amp (after replacing any defective components).
You can't check the transistors with power on the circuit. You can't test them definitively unless you remove them from the circuit.
with all parts in the circuit, all 4 bias turned all the way down and the emitter(1) & collector(3) of Q-407 shorted the current draw is the same.
If it produces relatively clean audio with the bias transistor shorted, check all of the bias components and confirm that you have a good connection between all of the various components. This would include the pot, the resistors connected between the pot and the bias transistor and the bias transistor.
with both output FETs out of the circiut the amp comes on and produces clean audio in the other 3 channels. when i put them in one at a time it does not pull current but with both the outputs in at once it will pull current. both the FETs checked out ok out of the circuit. when i installed only the N channel the bottom half of the wave was clean but when i installed only the P channel FET the wave was not so clean so i replaced it with a IRF9540N. now with only that part in the circuit the top half of the wave is clean. so i put both in at once and the same thing happens it starts pulling current (no audio).
Remove those two outputs. With the black probe on the gate pad for 540 and the red probe on the gate pad for the 9540, what is the DC voltage?
There is only 35 volts across the gates of the to fets. The 9540 has 25v, the 540 only has -10v.
Is the 25v and the 10v the voltage with the black probe on the source leg and the red probe on the gate leg? If not, post the voltage measure that way (gate to source).
That doesn't look like it should be causing excessive current draw since the 540 is completely off.
If this amp doesn't use the MEHSA insulators, I'd pull the outputs out of another channel to see if they'll work in the defective channel.
If this amp doesn't use the MEHSA insulators, I'd pull the outputs out of another channel to see if they'll work in the defective channel.
It does use the mesha insulators. But I can still swap em around unless there is a problem with that. It wouldn't take long at all. I haven't tried using a new 9540, should I try that?
It's been proven repeatedly that the 540N isn't suitable. I don't know if the same goes for the 9540N. Using outputs from a working channel would help you determine if they're the problem. After removing the ones from the working channel, confirm that there is no leakage (meter on ohms) between the first leg and the other two legs of the transistors you removed. They sometime fail when you heat them.
Just to make sure that I haven't missed anything...
It produces the top half of the waveform perfectly with only the 9540 in the circuit.
It produces the bottom half of the waveform perfectly with only the 540 in the circuit.
With the bias transistor shorted from collector to emitter and both outputs in the circuit, it draws excessive current.
If that's true, how much current?
It produces the top half of the waveform perfectly with only the 9540 in the circuit.
It produces the bottom half of the waveform perfectly with only the 540 in the circuit.
With the bias transistor shorted from collector to emitter and both outputs in the circuit, it draws excessive current.
If that's true, how much current?
So far that all seems to be correct. I'm not sure how much current, it will pulsate. When I apply remote voltage it is okay for a few seconds and then it will suddenly start to draw current and the amp will shut off and it starts all over again. It will happen about every 5-6 seconds.
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