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Harman/Kardon 430 - Need help with strange powerup noise

speeddog

speeddog

New Member
Hi everyone,

I have an h/k 430 "twin power" receiver which has a strange powerup problem I've been trying to track down. When the receiver is switched on, after about 5 seconds, a hum/buzz is audible in both speakers for a few seconds. After the noise fades out, the amp sounds quite good and relatively quiet, with low DC offset (~10mv). I have replaced all the caps on the main amp board and both rectifier boards with new Nichicons, as well as replacing the four main power supply caps with new Panasonics. However, the powerup noise problem persists. Here is a link to a recording of the noise - you can hear the click of the amp power switch, about 5 seconds of silence, and then a series of about 4 swells of the humming noise, after which the amp quiets down:
https://soundcloud.com/user872357133/h-k-430-amp-powerup-noise

I was hoping to get some advice before beginning the arduous process of replacing transistors willy-nilly. It seems kind of odd that the noise is in both speakers, despite the "twin power" design of this amp. Thoughts?
 
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Switch click faintly audable, nothing else heard.

Until I get a pair of head phones and connect them to the laptop, the switch click is the only sound that I can hear with the laptop speakers. :sigh:

Mark T. :music:
 
Power supply and maybe more. Keep playing it and eventually outputs will go, too. Don't play it anymore. "smile"

Jaws: "sometimes the shark go away and sometimes he don't go away and then you hear that high pitch scream'in" "them eyes that roll over like dolls eyes"

right in your pocket book.
 
Binkman,

Any idea which component in the power supply may be at fault, given that I've already replaced the filter caps and electrolytic caps on the rectifier boards? Rectifier diodes? Just wondering if anyone's had a similar problem before.

Thanks!
 
I'm guessing no one ever found a solution to this? I have the same sound from a Harmon Kardon 430, except that it's only in the left speaker, and lasts for about 8-10 seconds on power up, then the music will kick in. The right speaker wasn't initially working at all, but both fuses were bad. Replaced them and the right channel sounds fine now.
The right is playing music fine the entire time the left one is buzzing. It sounds not unlike arcing. More than a little unsettling. The transformer on the left side is pretty rusty on the outside, so I'm worried it might be the issue.

Trash it?
 
Replace all small signal transistors in pre and power amp. These are always bad.

Ksa992 and ksc1845 is suitable. Although if I remember correctly the 992 isn't needed here.

There may also be bad diodes in the power amp. Use 1n4148.
 
Hi ZOOM, I took your advice and first focused on the left side of the power amp board. I got lucky I guess. I pulled the most suspicious looking component first and one that I had replacements for on hand. Diode D404. Had a lot of green corrosion on the leads. Tested it to be bad. Replaced it and the awful buzzing is gone!! Thank you!!
 
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