[B00TS]

Hi SeeSeventy,

I held off posting the other day as it seemed as though you were on track for a solution but now I think I'll offer my two-penny's worth!

I am an electronics engineer and have around 20 yrs experience in fault finding of this nature and so I would hope that I can help you get to the bottom of it.

The only sure-fire method for nailing faults like these is to break the problem down into logical sections and test and eliminate each potential candidate.

A reasonable multimeter is essential and it will be a struggle to put this to effective use without a wiring diagram for the system.

I would tend to agree about the amplifier itself being unlikely to be the problem, epecially as you say that the system is still capable of operating correctly at times. Much more likely that the problem is a chafed wire somewhere or a dicky connector. If the wiring can be proved to be ok, you'll have to start to consider eliminating the active stuff like the head unit and amp. As getting hold of substitute units for this is not easy, I'd hammer the wiring first.

One set of readings I would want to take would be across all of the speaker connections where they connect to the amp. Measure for resistance across each speaker channel. Left and right ought to measure similar values for each of the front and rear pairs.

Also measure between every speaker lead and chassis. There should be no path to chassis from any speaker wire. The meter should read over-range on resistance.

Because there is only 12v available in a car, most high powered amplifiers use a 'bridge' configuration for the amplifier outputs and this means that NONE of the speaker connections can be allowed to short to ground. If one is grounding somewhere, the amp will run hot and the sound quality will be diabolical.

Quite unlikely, but still possible, is that one of the speaker connections is touching 12v battery feed somewhere. With the battery disconnected and with the power switch for as many accessories as possible in the 'on' position , measure between every speaker lead and battery +ve. A short here will definitely make the amp feel and sound very poorly.

Any cross-connection of wires from one channel to another will also cause the amp to lose the plot. Again careful checking for shorts is needed.

It seems as though you have done a fair bit to eliminate the signal wiring between the head unit and amp but this should be continuity checked for open-circuit wires, shorts between wires and also unexpected shorts to ground. You will most likely need to 'extend' one of the meter leads and engage the services of a willing assistant for this one. Wiggle wiring as much as possible during each test.

If you can't get a wiring fault to reveal itself and you need to sub in an amp/head, I have a V70 with premium sound. If you're not too far away and our kit is the same (doubtful?), I'd be willing to let you try mine to eliminate yours. I'm in Gloucestershire.

Looking back over all your posts:

1. What is this 'extra' earth you have added at the antenna? I doubt this is related to the problem you're having but still, if there was not a problem with radio reception, why alter the earthing arrangement? You may have added a current path that the designer didn't envisage.

2. What, in your original post, is getting toasty hot?

Anyhow, enough of my rambling, I've got to go to work!

Hope the above gives you some food for thought...

Boots.