Harmon Kardon PM 645 Vxi issues

[veedubz1]

HI
i have had my Harmon Kardon PM 645 Vxi amp for ages and it has never given me any grief untill now
For some reason only known to itself only one channel is working
i have tried different source input and different outputs and still to no avail
could you please help me and tell me what i should check inside the amp
I am quiet techy but i have no idea what i should be looking for in an amp


many thanks
veedubz1

[llwhtt]

If you have not repaired any amplifiers before this is NOT the one to start with. To repair any of the usual amp problems the main circuit board needs to be removed and that mean disconnecting many many connectors and unsoldering many wires that don't have connectors. All of the circuit boards attached to the front need to come out including front panel. But first you must download the Service Manual and troubleshoot the problem. You'll need an o'scope and signal generator as a bare minimum. The amp and tuner I have were left behind because no Service Manual was available at the time, pre-internet. H/K was no help at all they didn't even have manual available. It wasn't until last year that I finally found the manual and got the amp repaired. I will never work on another one these again. All of these problems would not be problems if the damn thing had removable bottom cover. Sure was a cheesy way to cut costs. I don't want to say don't do it but this is a very challenging amp due the construction. Find the manual and then decide for yourself. I am willing to step you thru it if you want, maybe you'll get lucky.

Craig

[veedubz1]

hi craig
thanks for the reply
i have had a play about with it and it appears that the Right channel on both the out puts dont work
the left ones are fine it is very weird
i have downloaded the HK manual
and have it printed out
what do i need to check first
1- that there is a signal going in from the source?
thanks

[llwhtt]

If you can follow a schematic input a signal and follow it thru with an o'scope until you find where it stops. There are many ways to troubleshoot but since you have limited experience starting at the front and winding your way thru it may teach you more about the amp. The signal will be jumping from board to board and you may not be able reach every place the schematic leads you, just skip it and go on. Finding the problem may not be hard at all repairing it is another thing. Be careful and good luck.

Craig

[greg1964]

I have this same amp I got it because one side had no output. It turns out the balance pot. was dirty. With a can of tuner cleaner all you have to do is remove the cover and the pot. can be sprayed without removing any parts. good luck!