Harman Kardon AVR-7300 snap crackle pop !

[cheebster]

Hello ! I'm trying to troubleshoot an Harman HT receiver that's been sitting on my shelf for about 1 year now. I had it as my main receiver.. and someday it quit working.

Everything works, it's just audio has some evil noise in it, shrrrrekkk in the speakers, its very bad. I think it's badcaps, it happens in digital and analog inputs. It works fine for some minutes (just a few) and then stats doing it.

I've seen a few bad caps in there, replaced them (a year ago..) but the issue has remained, so i've missed something. I don't see anything visually bad.. and i got no ideas where to start. I've been doing meter tests on caps around but havent seen anything bad. If anyone has any pointers !

I took a few pictures and the service manual. If anyone has a clue i'd be quite happy to get this one going (this is a beast from 2004, their flagship receiver..)

I was also wondering.. eventually i was looking to buy an oscilloscope as ive never used one. I wonder if it could help me to fix this one by learning how to use and to find and fix the fault..



Here are the pictures :

http://www.fusioninformatique.com/temp/AVR_7300/

Thanks for any help !!!!!!

[Khron]

Re: Harman Kardon AVR-7300 snap crackle pop !

Especially where digital circuits are involved, power supply filtering caps should have minimum lead lengts, so if/when possible, they should be sitting directly on the board, not "flying"

Both the analog and digital inputs end up passing through the power amplifiers, don't they?

Does it output that sort of noise on all channels? Or just the (front) stereo pair?

Indeed, an oscilloscope would allow you to probe the (analog) audio signal from the outputs of the DAC's all the way to the speaker outputs.

Perhaps electrolytic signal coupling caps going dry?

[cheebster]

Re: Harman Kardon AVR-7300 snap crackle pop !

Okay. I might invest in an oscilloscope if it would help me get this one going as well..
I was looking at the Rigol DS1052E 50MHz DSO that is (or was?) hackable into a 100mhz version.

When you say the signal coupling caps, can you give me a pointer on where to look at ?

Tes, the analog and the digital inputs are passing thru the power amplifiers. i'd have to do a few tests (its been a while) to double check where the noise is going out of. I'll post back

[tom66]

Re: Harman Kardon AVR-7300 snap crackle pop !

Not sure how hackable the new Rigol scopes are - whether or not you can get 100 MHz.
However, I don't think 100 MHz is really necessary for audio, which is 20kHz max .

[Khron]

Re: Harman Kardon AVR-7300 snap crackle pop !

I was fortunate enough to get my hands on a superb Tektronix 2235 2x100MHz scope a couple months ago, for a measly 100eu (~130$)

And on the other hand... http://www.eevblog.com/2010/05/11/ee...oscope-please/

[budm]

Re: Harman Kardon AVR-7300 snap crackle pop !

Check the Audio line output to see if you do hear the problem there, then the problem is not in the power amp sections.

[cheebster]

Re: Harman Kardon AVR-7300 snap crackle pop !

budm, ah ! nice idea, thanks !!!

i will put this thing back together tomorrow if i have time and see if i can hear it there.

khron666, but the rigol one seems to have good reviews...

[Th3_uN1Qu3]

Re: Harman Kardon AVR-7300 snap crackle pop !

The Rigol is a good scope, he was just pointing out that you can get similar performance for a lot cheaper. Also, analog scopes tend to be better for testing audio equipment. On the other hand, with a DSO you can do a bunch more things that you can't with an analog, so it's your pick.

If it were me, i'd go for the Rigol, but i already have an analog scope.