HK Lucas Performer 900 amp fault

Hi

I have a HK Lucas Performer system where the amp module sits in the Sub with active outputs for the Satellite speakers. The amp is a 4-channel unit with channels 1 and 2 running bridged for the sub output and 3 and 4 providing the Satellite outputs.

I have an intermittent fault on the left satellite output part of which I am struggling to reproduce on the bench.

Firstly, does anyone have the schematics for the amp? The schematics and layouts for the mixer/filter section is in the service manual that is available in several places on the web, but I have failed to locate anything for the amp sections.

Otherwise has anyone come across the following issue / issues before and can point me in the right direction. I suspect that they are linked but not 100% sure.

From power up there is an intermittent crackle on the left satellite output that is independent of the volume settings and is still present when the internal ribbon cables are removed isolating the input/filter boards, so has to be internal to the main amp section.

In use after a reasonable period of use one channel (I believe also the left) drops to a very low level distorted version of the output. I have not been able to reproduce this drop out on the bench despite some reasonably hard running for as long as my ears can take it with a blanket over the amp, heating and freezing the board, flexing and tapping different sections etc.

As it is only on the one channel that rules out anything in the psu section.

None of the heating / cooling tapping flexing etc appears to affect the intermittent crackling, at first I thought that the cracking reduced with warming, but now I am not so convinced.

The amp does sound very good through my test setup and I feal is very worth trying to get to the bottom of.

HK do still sell a replacement amp module but at well over £1k that is not going to happen.

All suggestions / ideas gratefully accepted.

Thanks

Richard

so to be absolutely annoying as soon as I start to pump in a sinewave (or square wave or sawtooth) the cracking stops completely.

It doesn’t appear to matter what frequency I pump in but a single frequency appears to be stopping all signs of the crackling and breaking up.

With a music signal I did get to the point where it was on the verge of cutting out, the crackling would get more consistent and for a brief instant the audio would kind of reduce and dip into the crackling and then come back good again. Much harder to explain that it should be 😊