If the 56 ohm resistors are within tolerance and you read ~56 ohms from the gate resistors (the ends NOT connected to the FETs) to ground, remove 4 FETs from each side.
Does it still draw more current when you reduce the power supply voltage?
Does it still draw excessive current at low output like before?
Does it still draw more current when you reduce the power supply voltage?
Does it still draw excessive current at low output like before?
No, they seem fine. Though when I started messing with it, it started doing two new things which is now 3 things it's doing randomly.
1) Didn't want to start and had excessive current draw.
2) Then did and everything seem to be fine without current going up when voltage descreasing.
3) Then doing what it was before.
I'm beginning to think there is something wrong with the regulated -/+ 15V supply as there are some 5W resistors that got very hot.
I will check further after the football game is over.
1) Didn't want to start and had excessive current draw.
2) Then did and everything seem to be fine without current going up when voltage descreasing.
3) Then doing what it was before.
I'm beginning to think there is something wrong with the regulated -/+ 15V supply as there are some 5W resistors that got very hot.
I will check further after the football game is over.
No, the power supply fets don't get warm. Not even under a light load.
Whatever weird behavior I had stopped. Maybe the fets were shorting against the heat sink when unbolted and pulled up and I just couldn't tell. The heat sink isn't ground though....
One of the 5W 270ohm resistors is getting very warm though. Warm enough I can't touch, quick measurement shows 140+. But the other does not. Am I to assume that maybe that's where my problem lies? Seems like a lot of current to warm up a big resistor like that one.
It was acting like it had a short and wouldn't turn on. That hasn't happened again.
What it does now is that when you drop the voltage, the current draw goes up slightly until about 12.2V and then the current starts to go down too.
The wave form looks the same.
The FETs do not get hot at any point, even under a load.
What it does now is that when you drop the voltage, the current draw goes up slightly until about 12.2V and then the current starts to go down too.
The wave form looks the same.
The FETs do not get hot at any point, even under a load.
Note the current (precisely) at various voltages. Reinstall the other FETs and compare the current draw. Is the current draw more, less or the same with all of the FETs in the circuit?
Do the FETs tend to heat up at lower voltage with all of them in the circuit?
I'm assuming you were checking the heating of the FETs with the amp out of the heatsink.
Do the FETs tend to heat up at lower voltage with all of them in the circuit?
I'm assuming you were checking the heating of the FETs with the amp out of the heatsink.
The current draw is intially the same but the peak current occurs at a different voltage. 3 FETs - 12V; 7 FETs - 11.2V Over time the current increases more with all the FETs in.
The FETs never heat up. I was testing them off the heat sink, but the outputs where still clamped down.
When I pull the whole thing out, it will eventually go into protect.
The FETs never heat up. I was testing them off the heat sink, but the outputs where still clamped down.
When I pull the whole thing out, it will eventually go into protect.
I replaced all devices in one of the channels, though not the drivers. I do have drivers on hand but not predrivers. Perhaps one is leaky? It will play for a long time without issue at low volume.
Current across the emitter resistors measure the same.
Pin 16 goes high when it goes into protect.
Current across the emitter resistors measure the same.
Pin 16 goes high when it goes into protect.
Have you tried driving a sine wave into it just to the point where it's drawing excessive current but isn't tripping the protection circuit and, at that point, measuring the voltage across the emitter resistors to see if one or two are higher than the rest?
There's a resistor between the emitters of the drivers in many amps that help shut down the drive between phases of the signal. If it's open or out of tolerance it could cause this type of problem. It's generally between 120 and 330 ohms.
If none of that helps, post a photo of the audio section.
There's a resistor between the emitters of the drivers in many amps that help shut down the drive between phases of the signal. If it's open or out of tolerance it could cause this type of problem. It's generally between 120 and 330 ohms.
If none of that helps, post a photo of the audio section.
That resistor seems fine. And both read the same voltages respectively.
Driving the amp with a sine wave, I do find that one transistor is excessive. I'm sure it's bad as the voltage goes up significantly on it and down on the others. I'll be replacing that one and trying again.
Is this a common problem with Darlingtons making it had to detect leaky transistors out of circuit?
Driving the amp with a sine wave, I do find that one transistor is excessive. I'm sure it's bad as the voltage goes up significantly on it and down on the others. I'll be replacing that one and trying again.
Is this a common problem with Darlingtons making it had to detect leaky transistors out of circuit?
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