This amp came back with 1/2 the PS fets blown. I replace the bad bank of FETs, the driver MPSA06/56, and 10ohm gate resistors. Pull down resistors are good measuring 820ohms. Drive signal to the PS FETs looks OK, but the fets run hot at greater than 13vDC at B+.
I replaced the 1n4742 diodes, checked the 10ohm resistors to PNP collectors.
The amp appears to be able to pass audio under mild bench load just fine.
As soon as more than 13vDC enters the amp, the FETs heat.
Removing the rects and the PD Fets never heat (Though fets gets driven to 100%)
If I mount the amp to a sync, it'll hold for a bit; but I'm afraid it'll come back (again) once strained.
I replaced the 1n4742 diodes, checked the 10ohm resistors to PNP collectors.
The amp appears to be able to pass audio under mild bench load just fine.
As soon as more than 13vDC enters the amp, the FETs heat.
Removing the rects and the PD Fets never heat (Though fets gets driven to 100%)
If I mount the amp to a sync, it'll hold for a bit; but I'm afraid it'll come back (again) once strained.
BTW here is the original thread for this amp.
https://www.diyaudio.com/community/threads/orion-hcca-225-gen-2.397406/
/Reply to that thread please.
https://www.diyaudio.com/community/threads/orion-hcca-225-gen-2.397406/
/Reply to that thread please.
I don't understand the request to reply there. Have a moderator move it if you want this in that thread.
This is PAM and the PS FETs will heat up at some input levels because the drive voltage will be just at the threshold of the FETs (maybe about 4v amplitude of drive). You can determine if that's possibly the problem by watching the drive level vs the heating.
Both banks of FETs should heat at about the same level (not one side heating while the other is staying cool).
This is PAM and the PS FETs will heat up at some input levels because the drive voltage will be just at the threshold of the FETs (maybe about 4v amplitude of drive). You can determine if that's possibly the problem by watching the drive level vs the heating.
Both banks of FETs should heat at about the same level (not one side heating while the other is staying cool).