[acwd1950]

I got this HK 730 and earlier this year the left channel quit. Well I took the top off and both fuses on the power supply for the left channel had blown. Replaced them and it was working again but it has lots of cracks and pops in that channel. It played maybe five minutes and blew the fuses again. So I swapped it of for another receiver. Well yesterday I got it out and put fuses in the left channel and hooked it up to a different pair of speakers. Didnt blow any fuses played it for about an hour or so, but it still has this crackling noise in the left channel dont notice too bad playing with the volume about third way up but with no volume up to that point its pretty bad. I have cleaned everything. Could the caps and rectifier bridge be causing this noise? Right channel is dead quiet! Any suggestions??

Thanks
Steve 

[AVnerdguy]

More likely the output transistors are breaki ng down under load. Usually if the caps go bad you'll get a nasty hum and it stays there. The rectifiers usually don't go intermittent. I used to love servicing those old HKs.

[acwd1950]

It sounds like its on AM that what it really sounds like. Its like a hissing with some pops and cracks. Thats with the volume all the way down. How do you check the bias on the output transistors? I got a tech manual for it and read that how to do it but I must be doing something wrong because I dont get a reading on the meter.

Steve

[AVnerdguy]

To check bias on the outputs is a matter of using a good VOM and putting one lead to GND. With the other lead you measure the 3 leads of the transistor. One lead (actually the metal tab of the case is the collector) will be very high as it's part of the voltage rail - I'm trying to remember what the 730 was - 45-50VDC should be about right. The other 2 leads are the emitter and base. There will be a potential difference of .7VDC between them. It could be positive or negative depending on the transistor - NPN or PNP.

If it's a NPN the base will be .7VDC more positive than the emitter - example - if the emitter reads +10.2VDC then the base would read approx. +10.9VDC.

However, when those transistors get noisy and start breaking down they still measure good DC voltages. What you need is a scope so you can see the AC signal as it goes through the chain.

[Venkman]

I realize that this is an old thread, sorry!  I have a 730 and the push buttons on the front are pretty finicky.  Try fiddling with the push buttons, especially the mono button.  Push them in and out 20 times and see if it clears up your sound.  If you listen at low volume and gently push the button(s) in, you may be able to determine if, in fact the buttons are your culprit.  If you can hear the sound crackle as you push the button, you can take the front panel off and try to get some Deoxit inside the housing of each of them.  it should take care of your issue. 
 
Good luck!

[AVnerdguy]

I realize that this is an old thread, sorry!  I have a 730 and the push buttons on the front are pretty finicky.  Try fiddling with the push buttons, especially the mono button.  Push them in and out 20 times and see if it clears up your sound.  If you listen at low volume and gently push the button(s) in, you may be able to determine if, in fact the buttons are your culprit.  If you can hear the sound crackle as you push the button, you can take the front panel off and try to get some Deoxit inside the housing of each of them.  it should take care of your issue. 
 
Good luck!

True - a lot of components from that era suffered from intermittent channels due to dirty switches. I made a lot of money servicing those problems. However, his issue is blown fuse and that is indicitive of a much more serious problem.

[soundbitten1]

I have the 930 and it worked fine until the amp section quit about a year ago. I'm using it as a preamp now which performs nicely, but I sure do miss using the whole unit. 

[Venkman]

True - a lot of components from that era suffered from intermittent channels due to dirty switches. I made a lot of money servicing those problems. However, his issue is blown fuse and that is indicitive of a much more serious problem.

Well, I suppose it's a good thing I'm not a tech!   Hopefully the OP got this fixed. 

[AVnerdguy]

I have the 930 and it worked fine until the amp section quit about a year ago. I'm using it as a preamp now which performs nicely, but I sure do miss using the whole unit. 

If you're inetrested in repairing you may contact me via PM. I love working on those and I do it at a reasonable cost because I just like to see those units stay online.

[acwd1950]

Well I ordered new output transistors for it. They should be here next week. I ordered a set for a 930 that I bought off of ebay few years ago. It has a dead channel. I bought it "as is" because the guy didnt have the fuse holder caps for it. But  somehow I determined that it was a output transistor ( been few years ago that I worked on it). I got service manuals on both of them. Gives me a good reason to go see my uncle in Indiana!

Steve

[AVnerdguy]

Well I ordered new output transistors for it. They should be here next week. I ordered a set for a 930 that I bought off of ebay few years ago. It has a dead channel. I bought it "as is" because the guy didnt have the fuse holder caps for it. But  somehow I determined that it was a output transistor ( been few years ago that I worked on it). I got service manuals on both of them. Gives me a good reason to go see my uncle in Indiana!

Steve

Cool. Good luck. If you need any help let me know.

[acwd1950]

Nope that didnt fix it. Still makes the same noise! Oh well its been one of those days!!!

Steve

[jkelly]

I have a few 930's in the basement if you need one.

Jeff

[herb73]

I know this is an old topic, but I just want to throw my 2cents in
I have a HK670 I bought new in 1977 if memory serves me.
I LOVE this thing...using ads L570 speakers..
It rocks....I cant give it up!!
I've had probs with the push buttons on the front panel as well..
contact cleaner helps, but some of the switches are loosing their "spring"..
If anyone  ever has any of these swithes for parts, I'd be interested
Thanx

[nodiak]

I had an amp that developed those very symptoms (after 9 years). I took it to local tech, he determined it was some solder joints going bad from over heating. He resoldered them and it was good as new. I contacted the amp maker and he told me he had used some solder during the period when that amp was built that proved to deteriorate quicker than usual.

[CaryF]

Hello, AVnerdguy!

I've just registered to the forum, but am unable to look at profiles, otherwise I would have sent you a PM.  I just scored an HK 730 from the 'bay, purportedly in good working condition.  If the unit should need recapping, may I contact you for your services?

Thank you,

Cary