I believe I've fixed it. The suspect ANW12s were the problem. I replaced both with discrete parts and the amp is powering and staying up with all components installed.
Here it is. Definitely was the issue.
Now heres another issue perhaps quick fixable, but on the bench clamped with a 4-ohm bridged load(2per chan) via a 500w resistor supplying a 100hz sine wave; the power supply starts to crumble.
IRFZ44 with 220ohm 1/8w gate resistors. Several of the resistors start to seap smoke at about 3/4 to clipping, amp drawing 110A from the bench. Shut it down quickly. The IRFZ44s all testing OK. Some of the gate resistors are out of spec up to 240 ohms.
I'm thinking of dropping gate resistors to 47 or 100 ohm 1/4w.
Now heres another issue perhaps quick fixable, but on the bench clamped with a 4-ohm bridged load(2per chan) via a 500w resistor supplying a 100hz sine wave; the power supply starts to crumble.
IRFZ44 with 220ohm 1/8w gate resistors. Several of the resistors start to seap smoke at about 3/4 to clipping, amp drawing 110A from the bench. Shut it down quickly. The IRFZ44s all testing OK. Some of the gate resistors are out of spec up to 240 ohms.
I'm thinking of dropping gate resistors to 47 or 100 ohm 1/4w.
With no load, does lowering the 12v supply voltage force the power supply to go to full duty cycle?
Are any of the gate resistors heating up at the higher duty cycle (from low voltage)?
You stated that some (not all?) of the gate resistors were heating up. Does the signal on the gate leg of the corresponding FETs look any different from the ones that are not heating up?
You stated that some (not all?) of the gate resistors were heating up. Does the signal on the gate leg of the corresponding FETs look any different from the ones that are not heating up?
So the resistors don't seem to be heating up at full duty cycle under no speaker terminal load.
I'm afraid to load the amp again because if one of those gate resistors open up its game over for the PS FETs in this amp.
Most of the resistors are measuring 217ohms. 2 are measure about 225 ohms, and 1 is measuring 240ohms. I cant be sure exactly which ones were smoking off in reference to their current readings but definitely a few were letting go. They don't look burnt or anything so I cannot be sure which were smoking exactly. I cut the breaker instantly.
BTW on the second try, I did have the scope on one of the gates while under load. The PS did go to full duty cycle, ~100A pull from bench, and smoke was starting the second time.
All gates look the same on the scope under no load at 9 & 10v
I'm afraid to load the amp again because if one of those gate resistors open up its game over for the PS FETs in this amp.
Most of the resistors are measuring 217ohms. 2 are measure about 225 ohms, and 1 is measuring 240ohms. I cant be sure exactly which ones were smoking off in reference to their current readings but definitely a few were letting go. They don't look burnt or anything so I cannot be sure which were smoking exactly. I cut the breaker instantly.
BTW on the second try, I did have the scope on one of the gates while under load. The PS did go to full duty cycle, ~100A pull from bench, and smoke was starting the second time.
All gates look the same on the scope under no load at 9 & 10v
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BTW the second round I was also measuring rail voltage. It had gone up to about 50v on one side referencing non-bridging terminals.
And during the 1st round, I did peg clipping on the amp with load one time momentarily as seen on my scope.
And during the 1st round, I did peg clipping on the amp with load one time momentarily as seen on my scope.
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I ended up replacing all PS fets and gate resistors. Amp is stable now no issue. Must have been some of the gate resistors going out of spec or perhaps this amp had a mild suffering prior. Its fixed and working up to clipping at 100A pull under 2-ohm per channel load.
Did you use the same value resistors and FET part number?
Are the gate resistors still heating up?
Did any of the FETs check as being leaky between the gate and either other legs with meter on resistance?
Are the gate resistors still heating up?
Did any of the FETs check as being leaky between the gate and either other legs with meter on resistance?
I used IRFZ44N and I did drop the gate resistors to 100ohm 1/4 watt. Amp is running absolutely fine like this. No resistors are heating up. At full tilt the amp got to 100F and the 500W resistor used for load went to over 200F. The signal on the gates looked a tiny bit cleaner at full duty cycle but I didn't take a photo. If you look back at post #26, you'll notice the top of the waveform is thick in height. Not sure if that was the cause or the problem or anything, but after replacing parts that turned into a solid straight thin line.
I'll check the fets for leakage.
I'll check the fets for leakage.
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I hope this to be ok but I would like to thank you Dr Zeus, I appreciate you going step by step in your diagnostic findings as opposed to skipping details and just all of a sudden ask where you got stumped without regard to stating previous tests/changes/details/ect when no one had responded you still took your time with writing all that, very rare in this dsay and age. It helped me follow along blindly to learn this skill not to mention any future trouble shooting for someone with similar issue. Again thank you...... Of course Mr Babin thank you too, but I think that should go without saying!