Harman Kardon AVR 7500 Front right channel problem

IN-WondeR · Joined: 04 Nov 2014 Posts: 5

I have this very nice Harman Kardon AVR 7500 Surround reciever.
But right now it's not so great.

My right front channel had been acting up a bit lately, with a heavy crackling sound when powered on. Only the right front channel though.
It could play sound wnyways, but now after a move, it plays no sound or very low level sound only, but the crackling noise in the speaker has increeased so much I was sure it would pop my speaker the other day.

I have had the entire thing disassembled, and found only one resistor that needed resoldering on the main control board, nothing else noticable.

Is there anyone who have any idea what the problem could be???

If any more info is needed please let me know.

Thanx in advance.

IN-WondeR · Joined: 04 Nov 2014 Posts: 5

This is the sound that comes out of my front right speaker, when attached to the reciever. I cannot figure out what the trouble is. Other than I believe it's the front right amplifier that has a problem. Possible a MOSFET that is bad. But I have no way of measuring this.

http://youtu.be/FK_nQkOBQUY

If anybody have any idea what the problem could be, then please let me know.

jts1957 · Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away

Does noise continue if "pre" is isolated (unplugged) from "main?"
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Guest · Posted: Wed Nov 05, 2014 7:42 am Post subject:

No, then the sound dissapears.

IN-WondeR · Joined: 04 Nov 2014 Posts: 5

No when the pre outs are unplugged the noise dissapears.

jts1957 · Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away

a) Get an external audio amplifier with its own speaker. Plug its input into the right front "preout" jack and see if noise is present.

And/or

b) Take the output of a external preamp with an audio source connected and playing hooked to it and connect it to "main in," slowly raise external preamps volume and see if noise is present.

IF noise IS present on 'a' but normal audio is heard on 'b,' you have proven the amplifier portion of AVR is working and your problem lies before that point.
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IN-WondeR · Joined: 04 Nov 2014 Posts: 5

Ol, did a test. Used the right channel preout and connected it to the left channel inppu. The noise moved from the right to the left, so the problem is definetly before the amps them selves.

So I would think the problem is in the DSP board then.

jts1957 · Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away

My manual says 'preamp' in exploded views and 'processor' in schematics.
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IN-WondeR · Joined: 04 Nov 2014 Posts: 5

Ok. So if it's the preamp, I'm thinking it would probably be something like a capacitor that was the problem.

Do you have the entire service and repair manual for the AVR 7500??

jts1957 · Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away

Strange that ONLY one of the five channels is affected. Cap or a bad joint or a switching IC (but only one portion?) or a noisy op amp (but only one portion?).

http://elektrotanya.com/?q=showresult&what=avr7500&kategoria=&kat2=all
BOTH have 84 pages. Try the larger size one. Maybe it's somehow better resolution or more complete than the smaller one I downloaded.
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