Hello
I am working on a JL 1000/1 where I replaced all of the 2/3 way switches. It looked like the amp sat outside in the rain or something because all the switches had corrosion on them.
I tested the amp prior to replacing the switches and it powered up and played fine, although I didn't do a high power test.
Anyway, I replace all the switches and go to power it up to test. I usually monitor the amp with a thermal camera during power up and I notice one of the PS FETs getting hot. I power off and measure it, and it's shorted. I remove the bad FET and measure all the remaining PS FETs and they all measure OK. I try to power up again and now another PS FET is getting hot, ends up being shorted as well. I remove it and try again, it's like a chain reaction of failing PS FETs.
I decide to remove all the FETs and look at the gate drive. It looks unusual to what I'm used to seeing, square wave from 0V to 12V (or whatever my input voltage is). It is swinging from -13V to 14V. Is this normal? This is measuring directly across the FET from gate to source.
With all the original PS FETs removed, I put in two IRF7545, one on each bank of the PS and the amp powers up fine (idling around 2.4A). With the IRF7545s the gate drive still looks the same.
I'm not sure what happened to all the PS FETs when they were working before. The amp literally just sat in a box until the replacement switches came in. 😵
I am working on a JL 1000/1 where I replaced all of the 2/3 way switches. It looked like the amp sat outside in the rain or something because all the switches had corrosion on them.
I tested the amp prior to replacing the switches and it powered up and played fine, although I didn't do a high power test.
Anyway, I replace all the switches and go to power it up to test. I usually monitor the amp with a thermal camera during power up and I notice one of the PS FETs getting hot. I power off and measure it, and it's shorted. I remove the bad FET and measure all the remaining PS FETs and they all measure OK. I try to power up again and now another PS FET is getting hot, ends up being shorted as well. I remove it and try again, it's like a chain reaction of failing PS FETs.
I decide to remove all the FETs and look at the gate drive. It looks unusual to what I'm used to seeing, square wave from 0V to 12V (or whatever my input voltage is). It is swinging from -13V to 14V. Is this normal? This is measuring directly across the FET from gate to source.
With all the original PS FETs removed, I put in two IRF7545, one on each bank of the PS and the amp powers up fine (idling around 2.4A). With the IRF7545s the gate drive still looks the same.
I'm not sure what happened to all the PS FETs when they were working before. The amp literally just sat in a box until the replacement switches came in. 😵
Attachments
With no FETs in, I would have expected to see a full square wave but with FETs in the circuit, what you show isn't unusual.
That said, this amp has 4 banks. It's an h-bridge supply, not a standard push-pull with two banks.
That said, this amp has 4 banks. It's an h-bridge supply, not a standard push-pull with two banks.
Notice that they're logic level and low voltage. Also note the RDS(on). The IRF3709Z was the sub for the 3707 but they're getting harder to find as well.