Amp came in with low ohm light lighting up and barely any power draw. I found Q835 which is an FQP30N06L signs of overheating. I replaced this part with IRFZ44. The low voltage supply will turn on with 1A for 15 seconds. The new IRFz44 gets raging hot. I put a small sync on it for now.
The amp does fully power up but with Q835 overheating its not stable to test much out. Gate looks alright, a +4v square. It could be cleaner but seems to be alright. Drain is very jagged. Looks like a downward 2 steps. I would have expected this to be cleaner. First image is with REM quickly applied. Second image is after about 15 seconds. 10vDiv, 2uS. There is always about 13v on drain.
Gate resistor for Q835 is 47 ohms and absolutely fine.
The 0.1ohm resistor and 33ohm resistor near Q835 are good. All diodes before and after the low transformer are measuring OK.
U802 is measuring:
1: 13.6
2: 0
3: 5.01
OpAmp regulated voltage seems OK at +-14.6v
Any thoughts as to why Q835 is overheating?
The amp does fully power up but with Q835 overheating its not stable to test much out. Gate looks alright, a +4v square. It could be cleaner but seems to be alright. Drain is very jagged. Looks like a downward 2 steps. I would have expected this to be cleaner. First image is with REM quickly applied. Second image is after about 15 seconds. 10vDiv, 2uS. There is always about 13v on drain.
Gate resistor for Q835 is 47 ohms and absolutely fine.
The 0.1ohm resistor and 33ohm resistor near Q835 are good. All diodes before and after the low transformer are measuring OK.
U802 is measuring:
1: 13.6
2: 0
3: 5.01
OpAmp regulated voltage seems OK at +-14.6v
Any thoughts as to why Q835 is overheating?
I dont have any QFET/Logic fets.
Hmm.. I remember a similar problem I had with an Eclipse DA7122 where the low voltage supply in that amp had a failed FET, IRFZ44 also overheated but then an IRF540N actually worked just fine. That amp is still in service from what I understand over a year now.
I'll try IRF540N for now and see if it will hold.
Hmm.. I remember a similar problem I had with an Eclipse DA7122 where the low voltage supply in that amp had a failed FET, IRFZ44 also overheated but then an IRF540N actually worked just fine. That amp is still in service from what I understand over a year now.
I'll try IRF540N for now and see if it will hold.
