Instructables

How to Fix Your Stereo Amplifier (Harman Kardon HK 620)

Picture of How to Fix Your Stereo Amplifier (Harman Kardon HK 620)
My stereo amplifier quit amplifying over the weekend. The LEDs still lit up, and it would still pass audio through the "tape out," but nothing went to the speakers. So, I decided to take it apart and see what I could find...
 
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Step 1: Open it up

Picture of Open it up
Pull the cover off, and expect to find something obviously wrong.

When there's nothing obviously wrong, make disapproving noises and have your house-mate phone his brother to see if the brother still has an extra amplifier. When it turns out he doesn't, carry on to step 2.

Step 2: Vacuum out all the dust

Picture of Vacuum out all the dust
I've had this amp since at least 1996 and it's never been opened, so that's plenty of time to accumulate some serious dust.

Vacuum out all the innards. Wire it back up and be amazed that all the channels now work.

Step 3: Reassemble

Put the cover back on and reconnect everything. Expect another 10 years of service before next cleaning.

Update: It has stopped working again twice since I originally wrote this, and both times vacuuming it out has fixed it.
Jan. 2008 - vacuumed, fixed again.
Feb. 2009 - vacuumed, didn't fix, vacuumed more vigorously and it fixed
Feb. 2009 - a week later it stopped working, and I vacuumed it gingerly, which fixed it.

There's no visible dust inside the amp. I don't think it's a loose wire because "pretend" vacuuming (or shaking for that matter) has no effect.

I posted a question about why this work here:
My integrated stereo amplifier periodically stops working. Why does vacuuming it out fix it?
Brennn107 years ago
Same thing happens with my sister's digital camera. Dust accumulates and nothing ever works. I will definitely remember this for any problems I encounter with electronics. My, those are HUGE capacitors. -Brennn10
Aeshir Brennn107 years ago
Holy frack, yeah those are huge.
486dx4 Aeshir5 years ago
meh those are nothing, i picked up a couple of 500vdc 1200uf caps for my coilgun project and their almost the size of pop cans, and ive seen much bigger than them.
I've seen capacitors rated at 2vdc and 3000F!!!!!!! they are used in the industry like in trains?!
Kii Brennn107 years ago
Those look like power filter caps. You really do not want to mess around with them.
(removed by author or community request)
Have you ever thought that vacuuming might pull away the static charge?
Alesana4 years ago
Hi , my pioneer amplifier A-443 works fine but the treble and the bass not working. And also a tick sound from inside always 10 or 15 second before another tick sound. I love to put some bass on songs but only the volume control the sound. Can you help me please.

Thanks
Alesana 
My dad used to work for pioneer but then they went out of business in the UK so possibly could have asked him to have a look at any datasheets for it and common problems ;)
newtchewy337 years ago
i tried it on my hk 870 but it didnt work so i put a comp fan in it and now it works... but that worked in my pre amp though so thanx.
Oooo HOW did you do that?? I want to mod a case fan into both of my stereos (a sony and a kenwood)
i just found a space large enough to place the fan so that it blows across inside and wired it to an external power supply.
radium19623 years ago
I know this is a joke, but come on, don't waste our time. This is a site for learning. If I want cheeky humour I'd go watch The Colbert Report.
blahblah014 years ago
i dont mean to sound, well, mean, but i dont really find this of much help, because what if dust isnt the problem for other people?
jolshefsky5 years ago
Could you try the following two options: 1. Open amp and put it back together. See if that works. It may be time (i.e. overheating components somewhere, or some other problem.) 2. Rather than vacuuming, flex the circuit board and components gently: things you might bump with the vacuum. If this works, it might be a cold solder joint or a broken trace or solder joint. Try heating and reflowing suspiciously dirty joints and see if that makes the problem go away for a much longer time. Good luck.
daveanton6 years ago
did i miss something? Somewhere between STEP 1 & STEP 2 you: A) wired a different Amplifier in from said Brother B) did nothing And if you DID wire another AMP, wouldn't THAT be the very DEFINITION of INSTRUCTABLE? Or was this a VACUUM OUT THE RECIEVER INSTRUCTABLE? please 'splain Lucy.
ewilhelm (author)  daveanton6 years ago
I have clarified in the Instructable. I vacuumed out the amp and it started working again. In fact, the amp stopped working again about a month ago, I vacuumed it again, and again, got it working.
n0ukf ewilhelm6 years ago
I doubt it collected enough dust in that short time to be the cause of not working. More likely, you have a loose connection somewhere that was bumped when vacuuming. Or your outputs (transistors or integrated amp modules) are going bad and can't handle the heat of normal operation any more.

And you missed a step, wipe the dust off the outer cover.
486dx4 n0ukf5 years ago
i agree, but the dust could also have origionally caused overheating, i have an sterio amp i use for my guitar, probly built around 85, when i crank it up it starts to smell a bit kuz the dust burns, ive been meaning to take a can of air to it for a while now.
Aeshir7 years ago
My dad bought a Harmon/Kardon AVR 135 a year or so ago, just when everybody except my dad and brother (three other people in my family, including me) started to figure it out. The thing is, we never use any of the fancy controls for anything.
momsnacher7 years ago
that dynaco tuner is sweet. the kits were fun
acaz937 years ago
i will repair my amp after all thanx