Harman Kardon PM655vxi problem

[tmho]

I got a Harman Kardon PM655vxi integrated amplifier from a friend. The sound from it is very good. But the right channel stops working intermittently.

I have tested it with a headphone and so it is not be the problem of the right speaker or the source. I have done the DC balance adjustment and idling current adjustment. I have tried several times cleaning the switches with MG Super Contact Cleaner (https://www.be-electronics.com/product_p/801b-125g.htm). But the problem still exists.

When the right channel is not working and the "mono mode" switch is turned on, the right channel will have sound again.

Could someone please kindly advise how I can try to fix the problem?

[tmho]

Re: Harman Kardon PM655vxi problem

I just found that the problem is sometime the right channel is not working and sometime the left channel is not working.

[CapLeaker]

Re: Harman Kardon PM655vxi problem

did you check it for cold solder joints? Next time it acts up take something non metal, like an old toothbrush or wooden spoon an press a little around on these boards? Can you upload some high resolution, straight shot pictures here?

[tmho]

Re: Harman Kardon PM655vxi problem

did you check it for cold solder joints? Next time it acts up take something non metal, like an old toothbrush or wooden spoon an press a little around on these boards? Can you upload some high resolution, straight shot pictures here?

Thanks for your suggestion.
Actually, I had checked cold solder joints on the PCB which connect to the inputs. I don't have much experience on this. I found just a few suspected joints. I had resoldered them and the neighbouring ones but no luck.
Recently, somebody also suggested this to me and gave me a link (http://www.berlin-repariert.de/harma...f-empfindlich/). The link is in German which I cannot understand. But I can see that they were resoldering the joints on the main PCD. I will follow that. But before that I will take some photos and show here.

[CapLeaker]

Re: Harman Kardon PM655vxi problem

I did read that thread you posted above (I can understand German). Basically he cleaned these boards and then resoldered cold solder joints. There were 2 boards he worked on, pic 3 and 7. Sometimes you need a magnifier to see the bad solder joints.

[tmho]

Re: Harman Kardon PM655vxi problem

I did read that thread you posted above (I can understand German). Basically he cleaned these boards and then resoldered cold solder joints. There were 2 boards he worked on, pic 3 and 7. Sometimes you need a magnifier to see the bad solder joints.

Did he get the same problem I am having?

[madan1]

Re: Harman Kardon PM655vxi problem

If you have signal on the headphones, then check the output relays ( if this amp has such ). Those relays are between the power amplifiers and the speaker terminals. They switch on few seconds after the power supply and also are used to route the signal to different terminal configurations ( sp.A, spB, sp A+B, bridged, etc.. ). They also experience mechanical stress and tend to get cold solder joints. The symptoms are what you have described - signal interruptions to one or more speakers.

Another easy way to check if the signal is interrupted before or after the power amplifier is to measure the dc V on the speaker terminals. If there is no V then most likely the path is interrupted after the power amp.

[tmho]

Re: Harman Kardon PM655vxi problem

Thanks for your suggestion.
Actually, I had checked cold solder joints on the PCB which connect to the inputs. I don't have much experience on this. I found just a few suspected joints. I had resoldered them and the neighbouring ones but no luck.
Recently, somebody also suggested this to me and gave me a link (http://www.berlin-repariert.de/harma...f-empfindlich/). The link is in German which I cannot understand. But I can see that they were resoldering the joints on the main PCD. I will follow that. But before that I will take some photos and show here.

[madan1]

Re: Harman Kardon PM655vxi problem

Bad link, but if the amp is like this one

then the relays seem to be substituted with that rotary selector connected via the metal rod to the front panel.

[tmho]

Re: Harman Kardon PM655vxi problem

Thanks for your suggestion.
Actually, I had checked cold solder joints on the PCB which connect to the inputs. I don't have much experience on this. I found just a few suspected joints. I had resoldered them and the neighbouring ones but no luck.
Recently, somebody also suggested this to me and gave me a link (http://www.berlin-repariert.de/harma...f-empfindlich/). The link is in German which I cannot understand. But I can see that they were resoldering the joints on the main PCD. I will follow that. But before that I will take some photos and show here.

I have taken some photos of the PCBs. On those suspected cold joints, I have marked them with red circles.

[madan1]

Re: Harman Kardon PM655vxi problem

Leave that board for now.
If you can start the amp, see if there is any V on the output terminals when the channel(s) is experiencing the problem.

[tmho]

Re: Harman Kardon PM655vxi problem

If you have signal on the headphones, then check the output relays ( if this amp has such ). Those relays are between the power amplifiers and the speaker terminals. They switch on few seconds after the power supply and also are used to route the signal to different terminal configurations ( sp.A, spB, sp A+B, bridged, etc.. ). They also experience mechanical stress and tend to get cold solder joints. The symptoms are what you have described - signal interruptions to one or more speakers.

Another easy way to check if the signal is interrupted before or after the power amplifier is to measure the dc V on the speaker terminals. If there is no V then most likely the path is interrupted after the power amp.

Thanks for your reply.
I was told by someone that there is no output relays.
Will check the dc V on the speaker terminals later when I find it not working.
The picture you posted is the one I have.

[tmho]

Re: Harman Kardon PM655vxi problem

Leave that board for now.
If you can start the amp, see if there is any V on the output terminals when the channel(s) is experiencing the problem.

I have just opened up it. Will check that later when it has the problem.

[madan1]

Re: Harman Kardon PM655vxi problem

Check this board for bad solder joints and clean the rotary selector


p.s. just checked the schematics - the headphone signal comes from the same power amp that drives the speakers. This means that if you have good signal on the headphones, the problem occurs between the power amp and the speaker terminals (the outlined board on the picture).

[tmho]

Re: Harman Kardon PM655vxi problem

Check this board for bad solder joints and clean the rotary selector


p.s. just checked the schematics - the headphone signal comes from the same power amp that drives the speakers. This means that if you have good signal on the headphones, the problem occurs between the power amp and the speaker terminals (the outlined board on the picture).

Thanks for the suggestion.
I have already done some resoldering on the above suspected cold solder joints. Now the amp has been closed and hooked up again. I will follow your suggestion when the problem happens again.

[tmho]

Re: Harman Kardon PM655vxi problem

Thanks for the suggestion.
I have already done some resoldering on the above suspected cold solder joints. Now the amp has been closed and hooked up again. I will follow your suggestion when the problem happens again.

After about 10 days with no problem on the left or right channel, today I found the left channel with problem again. I was listening to songs using the AUX input while doing something on the computer. Suddenly, I found that it seemed no sound from the left speaker. I went to the left speaker and confirmed that there was no sound. Then I took out my multimeter and found the DC voltage at the left speaker was -36mV. But after less than a minute, sound was coming back from the left speaker.

Next time when I have time, I will open it up and check on the board suggested by madan1.

[madan1]

Re: Harman Kardon PM655vxi problem

I guess you will find similar mV on other channel, which basically means that the connection between the speaker outputs terminals and the power amplifier is fine. This also means that you should experience the same problem on the headphones.
Next time when the problem occur, plug in the headphones and see if they work.