Please Help! Harman Kardon HK775, problems

[tonyinfinity]

Hello, im in need of some advice, please. I bought this hk775 off ebay, and of course it was described as "works and sounds great!" Well i hooked it up to my center channel speaker, and as i was listening, i started to smell something. I thought it was the amp at first, but then i saw my speaker start smoking! Needless to say my speakers are cooked, and sound like sh*t. The amp did put out sound, but it didnt seem loader than my TV puts out, but i didnt really have much time to listen. So now i want to attempt to fix it. My skills are pretty limited. Im a NOOB. I have changed caps before on a Yamaha M-80 that i got for free, and ended up getting that working. Lucky find, i know! And it sounds awesome! Anyway, i did find the service manual for the hk775 on-line, so im able to refer to that. So here is my question.... Does anyone have any thoughts as where to begin with the repair? Is it the caps? Like i mentioned above, it does power-up, and made sound. The only test i have done so far is put a volt meter on the speaker terminals, without an input pluged in. It had a 16 volt output?! That seemed really high to me. I mean you can start a car off that! So now i have the cover removed, and debating whether or not to just start replacing capacitors? Any help would be appreciated! Sorry so long............

Tony

 

[XEAGLEKEEPER]

Sounds like you have DC voltage on the outputs.Put a DMM on the speaker out terminals both left and right select DC voltage to see if there is any DC (DC is not good tends to cook speaker voice coils).


Dave

 

[jaycee]

Unfortunately, it looks like you've been taken for a ride

If you are inexperienced, chances are you will cause more damage than you will fix. Power amps are not to be trifled with. Either find a good repair shop, or bin it/sell it for parts.

 

[XEAGLEKEEPER]

If you know how to check transistors.I'd start by checking all output transistors on the channel(s) with DC or find a repair tech if you have any doubts.Amps have serious fatal voltages present on the circuits as jaycee has already stated.


Dave

 

[taj]

Tony,

I have an HK770 that I'm currently fixing (very slowly) with a similar, possibly the same, problem. I don't know how similar these amps are, but the model numbers are pretty close.

See this thread. It has plenty of good reading to keep you going.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=93053&highlight=

 

[spind]

Here's another thread with some pictures and a link to the service manual.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=86584&highlight=

This may not be the easiest amp to play with if you are really inexperienced. 4 pairs of fast 2SC2564/2SA1094 output transistors---they are hard to find, but they seem to be available if you search. 3-pin emitter resistors may also be hard to find.

If you can get your money back from your ebay transaction you may be best advised to do that. Alternatively you should probably find a good tech.