Dear DIYers
I recently got a Harman Kardon PM 655Vxi amp "fully functional". It is needless to say, it wasn't. At first there was nothing, except a loud "bang" over the speakers when switched on. I carefully disassembled the front of the amp and could clean out the contacts of all those small switches and the rotary switches, too, with the help of different kinds of electrical contact cleaners. I was careful to cover the pcb and all other parts during that process.
After that cleaning process, the amp played. The sound is rich and delivers very clean, hard bass, which I never heard before from our Linn Keilidh speakers (I had been runnning those with a smaller HK receiver for many years).
Then the the left channel of the phono amp stopped playing. I disassembled the amp again and found some faulty soldering points around some transistors. After resoldering the phono amp works nicely again.
But there are still some problems left:
- firstly I still get bangs when switching the amp on and off. I tried switching it on, with the speaker output disabled (= set to headphones only), but then I get the bang, when switching the speakers on.
- sometimes I get loud noises in one or both speakers. The noise is immune to any volume level = it is the same, whether I have high or low volume. It comes and goes and does not seem to be completely related to heat or warming up of the amp, though I tend to say, that it gets less frequent, when the amp is warm (and boy, this thing gets warm!)
So, as I am not an electronics buff, I wonder about the origins of the different noises. The bang or pop in the speakers after power on/off could be produced by the speaker relays. I don't know, it is just a guess. I have no idea, how to replace these, as they don't seem to be available anymore.
The noise during normal use, could be either defective parts, like capacitors, or more defective solder points? Is there any way to get to know, what is the real problem, without being the electronics hero, which I am unfortunately not?
I could get it repaired, as there is exactly one shop in Germany, that does offer that, but the price is insane and I would be better off buying another amp. On the other hand I really love the sound of this amp and the power reserves it provides for drums or large orchestras.
So I would be very grateful for any hint, that might lead me into the right direction to further limit down the possible faults of the amp.
Thanks and kind regards
Ben
I recently got a Harman Kardon PM 655Vxi amp "fully functional". It is needless to say, it wasn't. At first there was nothing, except a loud "bang" over the speakers when switched on. I carefully disassembled the front of the amp and could clean out the contacts of all those small switches and the rotary switches, too, with the help of different kinds of electrical contact cleaners. I was careful to cover the pcb and all other parts during that process.
After that cleaning process, the amp played. The sound is rich and delivers very clean, hard bass, which I never heard before from our Linn Keilidh speakers (I had been runnning those with a smaller HK receiver for many years).
Then the the left channel of the phono amp stopped playing. I disassembled the amp again and found some faulty soldering points around some transistors. After resoldering the phono amp works nicely again.
But there are still some problems left:
- firstly I still get bangs when switching the amp on and off. I tried switching it on, with the speaker output disabled (= set to headphones only), but then I get the bang, when switching the speakers on.
- sometimes I get loud noises in one or both speakers. The noise is immune to any volume level = it is the same, whether I have high or low volume. It comes and goes and does not seem to be completely related to heat or warming up of the amp, though I tend to say, that it gets less frequent, when the amp is warm (and boy, this thing gets warm!)
So, as I am not an electronics buff, I wonder about the origins of the different noises. The bang or pop in the speakers after power on/off could be produced by the speaker relays. I don't know, it is just a guess. I have no idea, how to replace these, as they don't seem to be available anymore.
The noise during normal use, could be either defective parts, like capacitors, or more defective solder points? Is there any way to get to know, what is the real problem, without being the electronics hero, which I am unfortunately not?
I could get it repaired, as there is exactly one shop in Germany, that does offer that, but the price is insane and I would be better off buying another amp. On the other hand I really love the sound of this amp and the power reserves it provides for drums or large orchestras.
So I would be very grateful for any hint, that might lead me into the right direction to further limit down the possible faults of the amp.
Thanks and kind regards
Ben