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Old 21st October 2007, 03:26 AM   #1
diyAudio Member
 
Join Date: Oct 2007
Unhappy HK AVR 335 Problems

Hello all:

This is my first post here, and after my searching, I have found that this may be one of the most constructive forums on the 'net (at least that I have found). So I'm throwing this out there and hope that one of you can help.

I have an Harman/Kardon AVR 335 receiver. This was given to me when it was thrown into protect mode after a lightning storm.

I took it to an authorized service center (out of warranty) to get a diagnosis. They gave me 14 parts that needed replaced. (12 transistors and a pair of resistors.) Once all those parts were replaced, the unit came out of protect mode, and played clean sound from the front two speakers only. (It also sent a LFE signal to subwoofer).

After checking all the usual stuff, I did a quick diagnostic using the 8 channel direct input to find that the 2 fronts and the 2 surround rear channels played clean, stable sound. The center and 2 surround channels make no sound in any mode, including the EzSet+. After taking it apart and checking the bias, there was NO voltage, whereas the other channels all had ~26mV.

After looking at the schematic in the service manual and visual inspection, the working channels and the non working channels are in two seperate "sets" on the main pcb board. Is there possibly a muting transistor that may be bad that controls this side of the amp?

Also, I found what I believe to be a short circuit on the bad "side". When i touch the leads of my dmm to these two seperate traces I get a definite short for a few seconds and then the resistance spikes and the short goes away. The working side does not show this on it's respective traces. What component could be failing that would cause this?

I'll be happy to post some pictures if anyone thinks they can help.

I've read some very informative posts on here, but my expertise is not electrical, so I'll definitely need some help here. Thanks!

P.S. After about an hour of playing the unit becomes unstable (at low volumes) and will stop playing altogether while it searches for a signal. This only happens after about an hour, so I'm sure it is a heat issue. A quick inspection revealed that the fans do not turn on. The fan connectors are also on the same main pcb as the amplifiers.
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