Harman Kardon PM655 Vxi left channel problem

Harman Kardon PM655 Vxi delay and left channel problem

The left channel of my captioned amplifier will stop working sometimes. I have tested it with a headphone and so it should not be the problem of the left speaker or the source. I have done the DC balance adjustment and idling current adjustment and the problem still exist. Could someone please kindly advise how I can try to fix the problem?

Try cleaning the switches, all of them. The HK integrated are notorious for this symptom. Have you tried isolating the amp from the pre amp using another source? I have a PM665 that periodically needs cleaning.

Yup, DeOxit the switches, especially the main/preamp and the speaker selector (at the end of the long shaft at the back of the chassis).

Thanks for suggesting cleaning all the switches. I have done that once a few months ago. I will do it one more time.
The left channel is also not working when I am using a headphone. Will that mean the speaker selector is not the cause of the problem?

Today, I just found out that if I press the "mode" switch to "mono", then the left channel works. Will that mean something wrong other than the switches?

No, probably still the switches. I've had that happen before, too. It's not easy to get the deoxit down inside the switches but once you do, work each switch about 50 times.

Good luck.

The advice about working the switches is for real. I think my PM665 has an issue with the PS caps or maybe a solder joint. I use the amp fed by a separate preamp but it still gets "crackly" at times. Trouble is, it sounds too nice to live without!

Finally, I have tired to clean all the rotary switches again. It was really hard to a way for the cleaner to get inside. The result is positive. Now so far for almost three hours of listening, I still have both left and right channel with clear sound. Thank you for your great suggestions.
However, I just found another problem. If the "phase control loudness" switch is not depressed, the left channel is louder than the right channel. As I mentioned, I only cleaned the rotary switches. For the push button switches, I really could not find a way for the cleaner to get inside. So far I am happy with the current situation when the phase control loudness switch is depressed. May be I will leave the push button switches for now until I found another problem.

Recently, I found another problem with the amplifier. I had read from this forum or somewhere else that there is a delay of several seconds from turning the volume up to hearing the sound from the speakers. I also had this experience and so I thought that it was normal. But recently, the delay is about a minute or more which I think should be something wrong. Didn't I clean the switches not good enough and cause this problem? Hope someone can help.

You'll really need to remove the faceplate and get ALL the switches' especially the push button switches. Yes, not easy to get the spray in there, but a MUST nevertheless. There could also be some issues with the protection circuit. There's a pair of small caps on the power supply side of the amp...near the rectifiers and filter caps, that were bad on one I restored. It wasn't a VXi though, so not sure if the same applies to yours.

jheu02 said:

You'll really need to remove the faceplate and get ALL the switches' especially the push button switches. Yes, not easy to get the spray in there, but a MUST nevertheless. There could also be some issues with the protection circuit. There's a pair of small caps on the power supply side of the amp...near the rectifiers and filter caps, that were bad on one I restored. It wasn't a VXi though, so not sure if the same applies to yours.

Click to expand...

Thanks for the reply. I did remove the faceplate (and even the bottom plate) in the cleaning. Will try again especially on the push button switches. Will also check if there are small caps on the power supply as per your advice.

The two small electrolytic ones 1/3 from the bottom of the photo in the link are the ones i'm talking about. Look for corrosion on the legs or bad solder joints.

https://www.flickr.com/photos/42311086@N07/8244874281/in/album-72157632173801246/

Today, I cleaned the push button switches, and I also did the DC Balance and Idling Current Adjustment again. After that, the delay is only a few seconds and the volume of the left and right channels are the same when the "phase control loudness" switch is not depressed. So far I am happy, hope it will last for some time.
For the two small electrolytic capacitors, I guess jheu02 is talking about the ones which are blue and I circled in the enclose photo. I could not find any problem visually. If the problem happens again, I will try to de-solder them and check if there is any problem with them.

Those are the ones, but they are a different color than mine were. I believe they are both Matsushita (Panasonic) but the lavender ones in mine had corroded leads and were "open", thus preventing the amp sectiong from working. Since you're getting sound now after the switch cleaning' it's probably not the caps.

jheu02 said:

Those are the ones, but they are a different color than mine were. I believe they are both Matsushita (Panasonic) but the lavender ones in mine had corroded leads and were "open", thus preventing the amp sectiong from working. Since you're getting sound now after the switch cleaning' it's probably not the caps.

Click to expand...

Thanks for your suggestion.
I am not that lucky. Today, I tried to turn on the amplifier. The delay is getting more and more. The most recent delay was 15 seconds and I think that it is not normal. I guess it is will get worse like before. Will those capacitors cause the delay?

They are part of the protection circuit if it's the same as the "plain" PM655. Can you solder?

jheu02 said:

They are part of the protection circuit if it's the same as the "plain" PM655. Can you solder?

Click to expand...

Yes, I can.

I would get a copy of the Service Manual (hifiengine might have one or check the digital docs database here) and also make a list of the other caps on the main board. Order up some new ones and recap at least the main circuit board. Here's a partial list of materials I used when readoing the basic 655. I don't know the specific differences between the two models. It's also only partial as I keep a partial stock of parts...ordering in bulk of certain values saves money especially on shipping costs. Also, feel free to substitute parts as needed. I have some "go-to" series of caps that I consider rough equivalents, so I'll buy on price if I can get a deal on one or the other.

Plan on keeping capacitance value the same as listed in the service manual (or as found physically placed in the board if it looks original). Companies made running changes that might not be documented. Voltage value of the new cap can be the same or higher than the original part, but don't go crazy. For instance, I don't buy 6.3V or 10V capacitors even if that's what the schematic calls for. They tend to fail sooner than higher rated caps. For those, I'll go 16V minimum, but may even use a 25V cap if that's what I have on hand.

Here's my recap thread:
http://www.audiokarma.org/forums/showthread.php?t=485506

Original problem thread with protection circuit:
http://www.audiokarma.org/forums/showthread.php?t=480122

And you already know which two caps were the issue with my unit.

Thanks for the information. Will do the recap later.
(Today the delay is about 30 seconds).

Hi
Just bought same H/K 655vxi amp.
I have similar problems.. the balance pot is super scratchy , also the MM phono section is too low volume and gives scratchy noise when there is no music.
There is layer of dust inside the amp (probably never opened ) but all the caps seems fine visually. going to deox it tonight and see if the problems are gone..

I was wondering what is the best way to discharge caps in these or is it necessary if you are careful