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Old 13th December 2012, 01:54 PM   #1
srinath is offline srinath  United States
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Join Date: Feb 2010
Default Harman kardon avr 7000 problems

This is a long story that has unfolded over about a month so please bear with me.

So I got the HK AVR 7000 broken off craigslist. It worked great in "surround off" mode, and was very weak in the right channel when it was in any surround mode, and was not doing surround at all. Optical input - same thing.
Now in 6ch input, it was perfect.
And headphones, never worked, it would flash HE on the display and back to what the display was showing, like say Tuner and station and breif burst of static in the headphones, and repeat

I isolated the issue to the dts board - and started to pull the receiver apart. Video board came off first., then the DTS board, and I should have tried to power it up and run speakers with the video board off but the dts in - I didn't do that. Anyway with the dts and video boards out, it powers up and tuner etc works as does switching inputs and surround modes etc, but no sound comes out. The safety relay clicks etc ... but no sound.

I thought that would not happen, I thought it will be making sound in 2 ch just fine. Anyway I guess sound has th go via the dts board no matter what, so I go on with its repair.

I find 3-4 swollen caps on the dts board, In the schematic these 4 caps are all 1000/6.3 and are all in 1 circuit. c65, c70, c73 and c170. They are in the +3v3a (c65) , +3v3d (c70 and c73), and +5vd (c170) section of the circuit. I suspect they are filtering of some kind, cos their other leg is to ground. So I suspect its losing some charge to ground and hence not supplying power where it needs to go.

I replace those and re assemble it, and the amp does not get past the standby stage.

So I pull the amp apart again, and I test it for power up with every component I disconnect. Nothing gets it to power up past stand by.

Then I find a 10000 mf 16v cap with the bulge on the main board. C520 as per the schematic. That now is on the filtering section of the 5vd, 3.3va, 3.3vd and 5vv lines.

So what is 5vd ? is it a way of identifying a 5v line ? its 5v but not the same as that other 5v over there ?
Then is 3v3d the same as 3.3vd ?

Now 1 swollen cap on these lines is a poor filter that has fried the rest of them down the line - I know that is possible. However is that enough to not let the amp power on ?

I am working on replacing that swollen cap, but would rather find all the problems right now and fix it instead of many more assemblies and disassemblies.

Thanks.
Srinath.
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