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Need advice to repair Hafler DH-200

74.92.128.149

Posted on June 24, 2013 at 11:27:06
HGS
Audiophile

Posts: 303
Joined: April 20, 2002
Hi. The amp gets hot on one channel pretty quickly and then the thermal protection circuit shuts things down. This happens with or without any input connected.

On the channel causing problems, the bias is not adjustable in range. Even at lowest setting, bias is about 10x manufacturer's spec.

My plan is to replace all the board components in the bias circuit. Can someone look at the schematic and tell me which components are involved with the bias circuit.

I am assuming that the PCB contains two circuits, one for bias and one for the audio signal.

Tha manual is available on the internet at:
http://www.hafler.com/techsupport/pdf/DH-200_amp_man.pdf

The PCB schematic is on page 14 of the manual.

If someone would highlight the bias circuit and e-mail that to me, that would be awesome.

And, am I missing something with my plan?

It seems like all 4 power MOSFETs on the bad channel get equally warm before thermal shutdown.

Thank you very much.

Howard

 

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