MA Audio HK4000

[Tom7227]

Good Afternoon gentlemen,

Working on tough amp repairs this Sunday, perhaps someone here might lend a hand.

This is an MA Audio HK 4000 amp, BIG (Class D amp)

There seems to be 2 issues with this amp,

First: The amp turns on, but there is a low level whine in the output,

This power supply has noise all over it, , I have resolder rails and can't seem to find the sourse.

Second: The amps shuts down when driven, no were near what power it can deliver . Part of the output seems to feedback into the power supply circuit, and I think this is what is triggering it...maybe

Tough working with no schematics..

Anybody, have a schematic, or possibly some experiance with this amp.

Tom

[Perry Babin]

I had a smaller amp doing this. The problem was defective filter caps. They looked perfectly fine but were open internally.

Connect the scope's ground clip (the one that attaches to the end of the probe) to the main ground terminal amp and monitor the ripple on the B+ terminal. If you see any high frequency hash, the B+ filter caps are likely defective. If it's clean, do the same test (monitor the secondary rail voltage) with the scope grounded to the secondary center tap. Make sure that the tap is at ground potential before connecting the ground lead for the probe.