Harman Kardon AVR 7500 Front right channel problem

Guest · Posted: Wed Nov 05, 2014 12:58 pm Post subject:

I can't download them. I failed the registration attempt, so I have to wait a few days.

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

After clicking on your choice of link...
Scroll to bottom (below "Document Preview" pane);
The line: "This file is downloadable free of charge... processing (please wait)"
will change to: "This file is downloadable free of charge... GET MANUAL"
Click on GET MANUAL;
Download as you would anything else you've downloaded via your browser/op system.
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Guest · Posted: Wed Nov 05, 2014 8:43 pm Post subject:

Cool, that worked...

Now I just have to find heads and tails of the service manual. Smile

Guest · Posted: Thu Nov 06, 2014 11:57 pm Post subject:

Must admit that my trouble shooting skills aren't what they used to be.

I'm struggling to find heads and tails in this.

Only thing I know is that it's not the amplifier itself that fails. It's somewhere between the pream and the volume control I think.

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

You'll need to create your own places to divide the circuit. Today's surface mount parts and double-sided or multiple layered PC boards do not make this easy. Looking at the block diagram is easier, but finding a convenient point in the circuit to electrically separate items will be harder.

Does noise appear in the headphone? If not, IC716 discrete buffer, or a surrounding part could be bad.

Floating the FR input or output pin at IC706 may also divide the circuit.
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Guest · Posted: Fri Nov 07, 2014 12:01 pm Post subject:

I will do a check of the headphone jack. If no noise there I'm pretty sure the problem is with IC716 as you say. I have looked over the entire block diagram, and as you say IC716 is the one that could be the trouble maker, and or the surrounding parts. Most probably the caps.

Guest · Posted: Fri Nov 07, 2014 10:06 pm Post subject:

I have now replaced all the caps surrounding IC716 (OPAMP) and it helped some. Now music comes out in the right channel, and at the right level. BUT, the crackling sound and so on still persists. So I'm thinking that IC716 has some trouble also, so I'm gonna replace this to, just to have a go at it.

I have yet to test the Headphone jack, to see if the problem is there also. If not, then it could only be IC716 (OPAMP) that is faulty.

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

You're going to a lot of trouble. If it turns out its crackling through the headphones, you will have done all that for nothing.
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Guest · Posted: Sat Nov 08, 2014 8:06 am Post subject:

I know. But I don't have a headphone jack at the moment. So I need to buy one before I continue.

Will get one later on today. But then again. Something must have been wrong there since the music now plays through the channel again.

Guest · Posted: Sat Nov 08, 2014 10:25 am Post subject:

Well, sadly the crackling noise is also in the headphones. SO now I need to go further back in the amp to find the trouble... Hmmm, damnit.