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I recently received an H/K 430 twin powered receiver from someone who hadn't used it in about 20 years, and it WAS working when they stopped using it. Now I hook it up after replacing the fuses and no sound comes out other than some low frequency noise that pumps the woofer cones like crazy and some harsh buzzing noises intermittently. Does anyone know what might be causing this? I know the easiest thing would be to take it to a repair shop, but I just wanted to work on this thing as a hobby. I've got a ton of capacitors and resistors from building headphone and class D amps, so I could repair it myself, but I don't have to knowledge to diagnose the problem.
Follow Ups:
1. Unplug the unit and open it up, spray clean all the control and switches, work them 10-20 times or so, check all the fuses ( there are lots of fuses to check!!!)
2. DC at output? it is ok if less than 0.2V, the DC can be adjusted if the circuit is ok.
3. You can use a pair of cheap headphone to monitor the sound, then try again to see any improvement. Use the tuner section instead of feeding external source.
4. Tell us the good news ( or otherwise )
To start with, I would spray out the controls and switches with d-oxit to eliminate that source of noise. Other than that, the only components prone to degrading from lack of use are the electrolytic capacitors, as others have suggested. I have fixed quite a few things by checking the 'lytics with an ESR meter, and replacing any that have a high ESR. Next to my DMM, the ESR meter is my most valuable piece of test equipment. If you plan on making this a hobby, you should consider buying one. Of course there are the extremists who don't bother checking them, and just replace all the 'lytics when restoring an old unit. (Nothing wrong with that, if you want to invest that much time and money)
Find the schematic if you're really want to gain some knowledge and diagnose the problem. I'd start at the power supply and go from there. Measure the DC voltage on the big caps (+/- leads) to see if you have voltage. So that AC is getting turned into DC. Big caps will definitely need replacing if you plan on making this a long term unit to use. As mentioned it's probably something in the PS or an output device.My experience with this amp was pretty thorough with a single unit. I rebuild one a couple years ago and it was a very nice layout, very easy to work on. One of the cleanest I've seen. It is well worth playing around with. After redoing the PS caps on my unit, I hooked it up to a restored pair of Spica TC50's and it was heaven. My brother in law liked it so much I made him a gift of it. The HK is one of the better vintage receivers I've had in my home.
I'm not sure if this is the same, but H/K has the Technical manual for download here:
May be it is hum you are describing. The usual cause for hum is the big electrolytic caps are near dead, but then, those ELNA caps are rather good - I recapped my 430 only last week and they even gave me an electric shock when I tried to remove them!
It's definitely not normal hum. It's more like very low frequency thumping that causes the woofer to bottom out. If I so much as touch a knob on the front panel, there's extremely loud scratching for several seconds and the woofer really goes crazy. I'm afraid to hook the speakers back up to it for fear of frying them.
a failing or bad driver or output transistor (or transistors).If the former, it could be related to cables or possibly even speakers.
If the latter, professional help is indicated.
N.B. The symptom you describe is NOT GOOD for your speakers. There may well be some significant DC getting to them. You can check with a DMM or VOM if you happen to have one.
One possibility for troubleshooting. IIRC, the 430 has pre out/main in jacks, no? If so, you can assess the function of the preamp and power amp separately.
Right on. I just checked with a DMM and I've got a fair bit of DC coming out of the one channel. The others seem okay. It figures the one channel I connected to test would be bad. If it's just a bad transistor I could replace that easily enough. Much thanks for the help. I'll post again if I encounter any other problems.
nt
all the best,
mrh
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