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?

[oldway]

Which input do you use? On tuner, aux, cd and AV audio, there is no electronic circuit before the mono stereo switch, just switches

If the fault occurs on these inputs, clean the input selector contacts, check the solders and cables that go to this switch or replace this input selector.

[abraxa]

Does it have speaker protection relays? In my Sony amp, the relay solder joints corroded over time, leading to the same symptom as you describe. Reheating them with the soldering iron fixed it, no relay replacement was necessary. Not sure if the same applies for you but it's worth checking and also worth checking if the relay contacts are at fault. Maybe in your case, the speaker relays do need replacement, who knows.

[abraxa]

http://www.hifi-forum.de/viewthread-220-4632.html shows the protection circuit, by the way. No relays in sight, so it can't be corroded relay contacts.

http://www.berlin-repariert.de/harman-kardon-pm655-vxi-ton-kratzt-setzt-aus-klopf-empfindlich/

Apparently, this guy had succes solving intermittent sound issues by reheating solder spots, too. However, he also cleaned some switches - though he doesn't specifiy how exactly. Also, his unit would produce sound when being knocked against until it would fade out into crackling sound again. I wonder if knocking temporarily solves your sound issues as well.

[tmho]

http://www.hifi-forum.de/viewthread-220-4632.html shows the protection circuit, by the way. No relays in sight, so it can't be corroded relay contacts.

http://www.berlin-repariert.de/harman-kardon-pm655-vxi-ton-kratzt-setzt-aus-klopf-empfindlich/

Apparently, this guy had succes solving intermittent sound issues by reheating solder spots, too. However, he also cleaned some switches - though he doesn't specifiy how exactly. Also, his unit would produce sound when being knocked against until it would fade out into crackling sound again. I wonder if knocking temporarily solves your sound issues as well.

Thanks for your reply. 
Actually, I have tried to resolder some of the soldering spots.  I will try some more as shown on that website although I cannot understand the language. 
Also, I have done the cleaning of switches.  But I am not using Deoxit which most people recommend.  Is Deoxit better than the one I am using.

[tmho]

Which input do you use? On tuner, aux, cd and AV audio, there is no electronic circuit before the mono stereo switch, just switches

If the fault occurs on these inputs, clean the input selector contacts, check the solders and cables that go to this switch or replace this input selector.

I have tried all the inputs.  They all will have the intermitten problem of one channel not working.

[tmho]

Today, I just found that this time the left channel is not working.  That means sometime it is working fine on both channels and sometime it is not working in one of the channels.