Advice re: trouble-shooting a Harman Kardon A-402 amp

Hello ... I’m new to the forum but it seems like I always end up here when I Google audio equipment

I’m looking for some advice re: a problem with my Harman Kardon A-402 stereo amp. I’ve had this amp since 1977. It sounds great and has been rock solid for almost 40 years! The only thing I have ever done to it as far as maintenance is blow the dust out and then squirt a little DeOxit in all the pots and switches every few years. Unfortunately ... I think it has finally developed a problem beyond cleaning and spraying DeOxit.

Last night I switched from AUX 2 to PHONO1 to listen to a record. I had been watching a movie on my laptop which was playing the audio through AUX 2 (no audio problems at that time). As soon as I switched to PHONO1 and the needle hit the record I noticed noise (distortion) ... and ... a lower volume level in the right channel (as compared to the left channel). I’ve heard this similar noise in years past which is when I cleaned and used the DeOxit. Anyway ... I went back to AUX 2 and heard the same noise/lower volume. So I think the initial problem stemmed from when I moved the FUNCTION switch from AUX2 to PHONO1). My first thought was ... OK ... the FUNCTION switch needs a little cleaning and DeOxit. In fact ... I don’t remember spraying the FUNCTION switch in years past since usually any noise problems I heard seemed to originate from the TONE DEFEAT switch or the from one of the eight switches to the left of the VOLUME knob. So today I did a thorough cleaning using my air compressor and then bathed all the pots and switches in DeOxit. Gave an extra squirt to the FUNCTION switch and worked all the knobs and switches real good to make sure the DeOxit got rubbed in. Hooked it back up ... I still have noise and lower volume level in the right channel :-( I’m pretty sure the problem raised its ugly head by more frequent use of the FUNCTION switch recently. I started listening to my records more about two weeks ago. So I am using the FUNCTION switch considerably more now going from AUX2 to PHONO1 (the FUNCTION switch didn’t get a whole lot of use prior to that ... at least not in the past 2-3 years. The left channel sounds fine. When I have the VOLUME knob at 12:00 (about half way) and start moving the BALANCE knob from the left to right ... full left sounds fine, about 10:00 the right channel sounds like it is beginning to be heard (light distortion), about 12:00 noticeably more distortion in the right channel, about 2:00 to 4:00 very noticeable increase in distortion and very noticeable that the volume level is lower than the left channel. Interestingly ... with the VOLUME knob a little beyond 12:00 (like 2:00 which is pretty loud) I hear loud hiss in the right channel ... like the hiss you hear between radio stations when dialing a tuner. This is particularly true when there is a source device (computer or phono) connected and turned on ... but not playing. So ... I hear noise and reduced volume in the right channel on all sources (AUX1, AUX2, PHONO1, TAPE1, etc.) ... and the noise does not change channels (it stays in the right channel) when I swap the input cables L/R. Thus I’m fairly certain the problem is either the FUNCTION switch, a blown fuse, or maybe a defective amp channel? I’ve used different cables plus I hear the problem through my speakers and my headphones. Any troubleshooting tips or advice would be much appreciated. Particularly ... testing for a bad fuse in this model (I guess replacing a fuse would be the easiest thing to try next?). If you think that might be the problem. BTW ... I’ve probably used this amp virtually every day since I bought it back in 1977 ... just to give you an idea of how much it gets used and how dependable it has been. Thank you. Whew ... sorry this post is so long!

I had a couple of these fine amps. I believe there is a board inside that connects inputs with pins into another board. You might need to remove the board and clean the pin contacts.


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Board that connects inputs

Hello ... thanks for the reply! When you say inputs ... do you mean like the AUX1, PHONO1, etc. inputs on the back of this amp? I think I see the boards you are talking about. One board is fairly big and all the inputs in the back are soldered to it ... the other board is small and has what looks like a ground wire and is connected to the board that has the inputs via what looks like what you call pins. In fact ... the FUNCTION switch is underneath the smaller board. Just as a point of reference ... the FUNCTION switch has a very long shaft that goes from the front of the amp to the back where the switch actually is (I think that's why I never Deoxed that FUNCTION switch till today ... because it is in the back and all the other switches/pots are in the front ... or maybe I never thought the FUNCTION switch needed contact cleaner because it was never "crackly". Anyway ... since I am just a novice I don't think I'm brave enough to try to remove the board to clean the pins. Maybe if I look at it a little longer ... or sleep on it I wish I could attach some pictures but I haven't had any luck yet doing that on this board. I need to figure that out! These ARE great amps! Thanks again for your reply! Oh ... and I gather you think the problem is not a fuse? Thanks!

Bad fuse would be total loss of sound on one channel or even both.


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Channel noise

Thank you ... that makes sense that it isn't fuse. I am going to try to post some pics later today. As an aside ... at one point last night there was a loud hum in both channels. That problem came out of nowhere. Never heard it before. I shut off the amp and turned it back on 15 minutes later and the hum was gone. But the right channel still has low volume and noise. I'm really bummed out. I just bought a new cartridge for my TT and some cork to make a mat. I was going to spend my Holiday installing the cart, making the mat, setting up the tonearm and kicking back and listening to some vinyl. But alas ... I'm not sure what is wrong with the amp. I wonder if anyone on this board can recommend a repair shop in Vermont or upstate NY area? I guess I could try to troubleshoot this myself but I'd have to learn a few things. I do have a MM. Anyway ... thanks so much for your help. I'll try the pics soon. Jerry.

EDIT

OK ... I’m trying to post some pics below with questions. Sorry if I’m mis-understanding anything:

Below is a pic of the source connectors on the back of the amp I think you’re referring to. The connectors are soldered to a board.



Below is a pic of the board that the source connectors are soldered to. The small board with the “ground looking” wire is connected to the source connectors board via pins ... I think.



Below is a closeup pic of the smaller board and a ten pin connector I think. The FUNCTION switch is to the left and under the small board.



Below ... in the top right corner of the pic shows some pins and white connector that connect the board with the source connectors to the small board (sorry ... not a very good pic).



So ... are all these pins the ones you are referring to as far as applying Deoxit to? If so ... I’m not sure how to remove the boards yet ... and assume that spraying while still connected is probably futile? Or if I’m totally wrong about all this just say so Thanks again for your help! Jerry.

Pics too big

OK ... so that didn't work. The pics are too big. Sorry about that. I should have resized and previewed before submitting. Maybe I'll try again later.

Fixed photo's

OK ... I think I fixed the photo sizes correctly. Sorry about before that. As an aside ... this amp now occasionally hums in both channels. It has never done that before. So in addition to the right channel having less volume than the left channel and exhibiting distortion/noise ... both channels occasionally hum :-(

I am going to suggest an alternative. This is a great amp, well worth repairing both correctly and going through it replacing caps as needed, noisy transistors or others out of spec, and reflowing the solder joints. Back then our tech found the HKs had more.than their share of cold solder joints. Those non-gold connectors tend to develop layers of corrosion causing intermittant dropouts. Other issues included the wire wrap system, a less than stellar system used by a number of makers.

None of the issues we ran into were related to the amp design but less than great construction techniques, a number of which plagued others trying to use them, just not mature enough.

Nice amp, wish I still had mine, one of my fave small amps. :thmbsp: Filter caps on mine went one day and I never got around to fixing it; I seem to recall that they were an odd value, difficult to source. Anyhow, it's about that age, I'd second the cap replace suggestion, including the filter caps, and going over the wire wraps (I hate them!). Worth fixing.

Recommend a repair shop in Vermont or Albany NY area?

Hi Brian ... thanks for the reply! Indeed this is a great amp. It has never failed to astound me regardless of what device I've connected to it ... be it phono's in the 70's/80's and tape decks, cd players and computers later! It has always been the go to amp for my DAW's playback when I need to assess recordings (I'm a musician). And of course for recreational playback So it is already being missed after just two days of problems :-(

I agree with you that a repair by someone that knows what they're doing would be best since I'm not qualified to do that myself. But I have no clue at the moment what the going rate is these days. I know it depends on the degree of problems and repair time. One thing I'm concerned about is taking it to just any repair shop as this amp to me is as precious as handing over one of my guitars to a technician for a repair. But this obviously needs a repair. Can you or anybody else on this board recommend somebody that perhaps lives in Vermont or the Albany NY area that I could take this amp too?

My other alternative is to buy another HK A402 used. I really have no desire to research other vintage models. I've been a guitar player for almost 40 years and have heard some great amps (I use mostly tube amps for guitar playing/recording) and this amp is about the best non-tube amp I've ever heard! I've always felt it had to do with each channel having its own power source (but that is probably the design for most good amps since the beginning of time ... I don't really know). Maybe I've just grown to used to its sound Makes me wonder if two of these amps could sound different ... which actually is probably the case. Anyway ... at the moment Im really torn on what to do. I can't go much longer though w/o a good amp! Thanks for the advice. It's much appreciated. If you or anyone else have a repair shop recommendation or know someone who wants to sell a used/working HK A402 for a reasonable price I'm all ears Happy Holidays! Jerry.

Caps ...

titanstats said:

Nice amp, wish I still had mine, one of my fave small amps. :thmbsp: Filter caps on mine went one day and I never got around to fixing it; I seem to recall that they were an odd value, difficult to source. Anyhow, it's about that age, I'd second the cap replace suggestion, including the filter caps, and going over the wire wraps (I hate them!). Worth fixing.

Click to expand...

Thanks for the reply! Good point ... big amps are overrated ... and small amps rule ... IMO. I lost a lot of my hearing to big amps in the 70's Seriously ... some of the best electric guitar tone is achieved by using lower volume amps to drive tubes, etc. Many of the guitar heavy rock bands that recorded in the 60's/70's were not using big amps in the studio. And those are the sounds we all know and listen to over and over again on vinyl, tape, CD ... and now iPods. Sorry ... I digress

If I remember correctly filter caps were made with different materials through the years (like paper caps in older radios?) and needed replacing. So do you think the noise I hear in the right channel (distortion, crackle, hiss) is likely from bad caps (not paper I know)? I'll bet the intermittent hum I suddenly started hearing could be caused by a bad cap. I seem to remember that being common in old radio's when you turn them on after sitting for many years in storage. You are correct about the age of my amp ... I guess it was time ... and overdue. Cleaning and DeOxit can only do so much Maybe I can find a good repair shop. Thanks again for the reply! Jerry.

Give the deoxit another try before you do anything else. I seem to remember that those switches were really, really hard to get clear. Something about HK and those little buttons that they liked to use -- they give me trouble on almost all HK stuff I've touched. I'd buy another A402 in a second if I saw one locally.

EDIT: Found that old thread from when my HK died -- almost 9 years ago now! Has a good link in it to a thread with some advice from EW on replacing the ps caps.

2nd cleaning and DeOxiting

Thank you for the help and the link! I used my air compressor to try to blow out any more dust then squirted some more DeOxit on all the pots/switches again. Unfortunately that didn't do any good so then I removed the Equalizer Amp P.C. Board from the Function Selector Switch P.C. Board and cleaned the pins and reseated (per ikorman's kind suggestion) but I still get low volume and distortion in the right channel plus intermittent hum in both channels. Is there anything else I can do to test this further to isolate the problem? For instance ... the intermittent hum gets louder and softer as I dial the volume control. Would that indicate a power supply problem ... or something else? I now have the service manual and am giving some thought into trying fix this amp myself or at least try to figure out what the specific problem is before I proceed in taking it to a repair shop ... or buying a new amp ... once I can save up some $ If anyone has any further suggestions ... or can point me in a direction to try to isolate the problem in the right channel ... feel free to advise. Now I'm going to put my head back into the service manual Thank you. Jerry.

Do you have any other amps? If so, try to see if it's the preamp section or amp section that gives the issue. There are jumpers in the back you can use to separate the two.


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Another amp

Hello ... unfortunately the only other amps I have are two guitar amps. I have an old VCR and tape deck with rca's but I assume those wouldn't work even for testing (like for testing the preamp out stage)? If I can borrow a stereo amp how would I hookup the borrowed amp to my HK i.e. what rca source outputs on the borrowed amp are used to connect to my HK Main Amp Ins ... and likewise where do my HK Preamp Outs connect to the borrowed amps inputs? Sorry for the ignorance. I've never used the jumpers on the back of this amp (pic below). Also ... can you give me an example of how the jumpers on the back of these amps are typically used? Maybe that would turn on a light bulb for me As an aside ... can you recommend a good website that has pics of how to discharge caps and then test them? I've been looking but haven't found a website yet. I'm beginning to think the problem could very likely be one of the four filter caps ... but I'm just guessing. Anyway ... I will see if I can borrow another amp first to test the preamp and main amp. Thanks again for your help! Jerry.

You need another amp with pre-out and amp-in connectors or a separate power amp and preamp system. To test your preamp, unplug both jumpers, plug pre-outs using an rca cable into another power amp hooked up to speakers. Or into amp-in of another integrated amp, also with speakers. Play something, inputting into your broken amp. Check all inputs. If the issue persists, your preamp section is bad.
To test amp portion, use another preamp or pre-out to plug into amp-in on broken amp, speakers connected to broken amp as well. Inputs go to the good amp. If problem persists, it's your power amp section.

You can't test caps without very specialized equipment. And without desoldering them.


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Preamp and caps

Ahhh ... thank you for the clarification ... I understand now about the preamp/amp test. I hope I can find a another amp with pre-out/amp-in connectors. As for the caps ... I'll put that on hold for now. Also ... I guess if it were a filter cap it would be one of the two on the right channel? Do bad filter caps emit a fuzzy or distorted or crackling with lower volume levels (or all of the above)? Thanks! Jerry.

I have two A-402 amps (and two of its little brother, the A-401). If your tests reveal the pre-amp section is good, you can try cleaning the power amp board multi-pin connector. It can corrode and cause the symptoms you've described. Unscrew and carefully remove the power amplifier board and thoroughly clean the contacts.

obcbeatle said:

Ahhh ... thank you for the clarification ... I understand now about the preamp/amp test. I hope I can find a another amp with pre-out/amp-in connectors. As for the caps ... I'll put that on hold for now. Also ... I guess if it were a filter cap it would be one of the two on the right channel? Do bad filter caps emit a fuzzy or distorted or crackling with lower volume levels (or all of the above)? Thanks! Jerry.

Click to expand...

If you have a soldering iron, you can swap these larger caps around from one channel to another to see if the problem stays or follows. But didn't you say you have issues on both channels at this point?

PS. Desoldering those big caps is a very trying task, if you haven't done much soldering.


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DaveVoorhis said:

I have two A-402 amps (and two of its little brother, the A-401). If your tests reveal the pre-amp section is good, you can try cleaning the power amp board multi-pin connector. It can corrode and cause the symptoms you've described. Unscrew and carefully remove the power amplifier board and thoroughly clean the contacts.

Click to expand...

Thanks Dave ... would that be the Main Amp P.C. Board (per the service manual) ... pic below (has two white 7 pin connectors ... one on the left side and one on the right side in the pic below ... C03/C04)? Thank you! Jerry.