Problem with Harman Kardon AVR 2550

Richsav730

Novice Member
I recently took over an older Harman Kardon AVR 2550 and 2 Sony EX700 AV speakers from an acquaintance who used the combo for stereo music listening only. I set up the system together with some small serially wired LG home theatre speakers (to raise the impedance from 4 to 8 ohms) and immediately discovered there was no sound from the left back speakers. I swopped the speakers for working ones and changed the wires but that did not work and it is clear the problem seems to be an amplifier one.
But that is only one issue, the system worked just beautifully on straight stereo sources for three days but while I was listening to some music from a local FM station a loud thump came from both speakers followed by an immediate drastic drop in volume and there was virtually no lower range. Turning up the volume to max didn't help. I also note that on 5:1 sources the centre and back right speakers have normal volume and tonal range, so it seems the problem is confined to the front and back left. All the panel lights and systems work just fine apart from one instance where a "protect" sign came up very briefly. In addition when the tone and balance knobs are twirled thumps and volume changes occur. I checked the Sony speakers and leads but they work just fine with the very low power Samsung home theatre system I used previously.
Any ideas guys?
 

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