Cornwalled Posted May 18, 2009 Share Posted May 18, 2009 Hello, Found a Harman Kardon 430 Twin Powered Receiver while dropping off junk for the township spring cleaning. It's missing the case, top and bottom. Otherwise it looked clean, so I figured I'd give it a shot. Got it home, discovered both power supply fuses were missing. That lowered my expectations for the unit. Replaced both, powered it up only to find it came up just fine! I hooked it up to some junk test speakers to hear how it sounds. All lights are good and FM reception seems pretty good. Even got the mute working. The volume is very scratchy, as well as all of the push button controls. However, after a few minutes, trouble began. Static started coming out, VERY LOUD! No amount of fiddling with buttons or knobs could make it go away. In fact, even after turning it off, the static and popping persisted for several seconds until the power supply discharged. My question is this: is this thing worth messing around with, or should I just send it back from whence it came? I'm afraid that just cleaning contacts isn't going to do it. I originally thought I'd use it to power the Cornwalls til I finish repairing an old tube amp. Now, I'm afraid to let it anywhere near them! Any thoughts? -Jon Quote Link to comment Share on other sites More sharing options...
jamesV Posted May 19, 2009 Share Posted May 19, 2009 My question is this: is this thing worth messing around with, or should I just send it back from whence it came? Are you going to fix it yourself? If so, if you have the time, I say go for it. I currently have the 730 hooked up to Cornwalls and love it. I also have a 930 that a friend picked up for me last year but isn't working properly. It needs some work and I can't wait to compare the two along with the other receiver that I have. Good luck... James Quote Link to comment Share on other sites More sharing options...
mr_eric_s Posted May 19, 2009 Share Posted May 19, 2009 How long has the unit been sitting unused? I'm an electronics novice, but I wonder if that sound might be the old caps inside trying to reform as power is applied? You'll want to Deoxit the dickens out of those push button switches; I've seen a HK430 and a HK75+ that got a lot quieter after that procedure. Quote Link to comment Share on other sites More sharing options...
Cornwalled Posted May 19, 2009 Author Share Posted May 19, 2009 Hello, As far as fixing it myself goes, I'm not very knowledgeable with solid state gear. I'm really better with older simpler tube stuff where density isn't as high, and parts are larger and easier to get to. I was thinking the same thing about the de-oxit. The thing that concerns me is those blown fuses. That makes me think something went way wrong and it pulled some pretty good current. However, in the time I had it on, it never drew more than a 1/4 amp through the isolation transformer I had it plugged into, even during the static. So, perhaps it is dirty controls. I've just never heard a dirty control be that loud! The only thing that made it stop was turning off the speaker switch, which if course disconnects the speakers. I was afraid I'd blow the speakers it was so loud. Scared me and the cat..lol I think I'll bring it over to my Dad's where he has more room to work on it. I'll shoot it up with some De-Oxit, and if that doesn't take care of it, I'll get rid of it. I'd rather dedicate my time to repairing the tube amp instead. If I do decide to get rid of it, does anyone here want it? -Jon Quote Link to comment Share on other sites More sharing options...
ace168516 Posted May 19, 2009 Share Posted May 19, 2009 Clean all the pots and switches with Deox-It...it is not uncommon for static to be caused by a bad switch contacts in older solid state gear. If that does not do it, inspect all the caps especially on the preamp and driver boards...some of them are not that hard to replace with even moderate soldering skills...nothing like an amp these days. Also check the DC offset with a multimeter...usually pretty easy to adjust on an older unit. ACE Quote Link to comment Share on other sites More sharing options...
Cornwalled Posted May 19, 2009 Author Share Posted May 19, 2009 I haven't cleaned it yet, but I did inspect the fuses. It turns out it blew another power supply last night when I was testing it. So, it's obviously got a fairly substantial problem. I don't think I'm gonna mess with it. I read online that transistors need to be replaced on these from time to time, and the amp has to be biased. I would have no idea how to bias a solid state amp. Nor do I know how to check DC offset. It sounds like it's probably over my head. I did find a service manual for it and will see if I can make any sense of it. -Jon Quote Link to comment Share on other sites More sharing options...
Marvel Posted May 19, 2009 Share Posted May 19, 2009 The caps need to be replaced, for sure. Not just the PS caps. It would be more time consuming than costly. Quote Link to comment Share on other sites More sharing options...
Cornwalled Posted May 23, 2009 Author Share Posted May 23, 2009 Hello, I've decided not to mess around with it. If anyone wants it, they can have it. -Jon Quote Link to comment Share on other sites More sharing options...
ace168516 Posted May 23, 2009 Share Posted May 23, 2009 If it was local I would take it, but not worth shipping something that may be hosed. For future reference, checking the DC offset is very simple and something you want to do on any old amp to make sure there is not DC going to the speakers...take a multi-meter, put positive and negative clips in speaker terminals, fire up amp with volume completly down and something null on the input (not phono). Fire it up and watch the numbers till they stabilize...atleast 10 minutes, up to an hour. A service manual will tell you what the range should be, but a good guide is less than 100mv, it is just old and probably needs adjustment or caps, under 50 mv, good condition of the components. Actual voltage in terms of v, not mv = speaker killer. Usually there are pots for adjusting offset and bias, bias is usually measured on contacts internally. Hope someone will find a use for it...I hate seeing vintage stuff die. Quote Link to comment Share on other sites More sharing options...
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