Does your unit have a headphone socket?Not all versions had this feature,but if your's does,and sound is ok from both channels via it,it would give a clue as to where the problem lies.

Also,you could try connecting something to the "aux" input socket,eg phone,tablet etc to see if the sound via that source is ok?

It seems odd that both bass and treble are effected,as separate main amplifiers are employed for each.

Does the unit appear to have been interfered with previously?You may need to carefully check around inside for anything that doesn't look "right"

Nick

Hi Nick, thanks for replying.

No, no headphone socket. I don't currently have an Aux cable, but looking at the circuit diagrams, both Aux, CD and radio come into the same part of the circuit. Radio audio is doing the same thing, no bass, only damaged sounding treble.

I opened it up last night, quite tidy and clean inside, very little dust. A little water damage on right hand side (working side), but only on speakers, and amp was clean.

Tried to fix the door issue by removing the gearbox and cleaning the wheel which the sensor picks up - what a pain in the neck to reassemble! - did not work either, so that's for another day. Could not see anything obvious on the amp board, or any other part of it. All cables seem secure.

Following the circuits in the service guide, I guess I'm at the stage of trying to read the output from the main switch/eq/amp part, or possibly swapping the speaker sets over to see if that changes anything.

While I understand how speakers work, can they "blow", and not make noise? Because like you say with seperate amps for everything, but the tweeter making some noise it's either the output stage/switch/eq, or somehow damage to both high and low amps on that side. Or if it's a real thing, somehow blown left hand speakers. 

I think I'm going to need a multi-meter and lots of patience. 

Any other ideas would be helpful, or if someone has come across this kind of thing before - I'm really confused as to the poor sound coming out, rather than no sound.

Cheers,

Mark

Well my efforts on the gearbox seem to have paid off. I mistakenly thought it would shut the door immediately on power off, but it waits for a few seconds and at 11pm after spending an hour trying to put the gearbox back together I was not thinking clearly.

Door is now behaving quite well, along with the sensor and CD mech, smooth and doing all the right things.

Radio is garbage, even with active antenna, however that's at the bottom of my priority list. Who listens to radio? :-)

Playing some CDs at volume and I must say the sound is quite good despite only having right channel operating. So I'm quite keen to get it operating properly.

Found the issue. It's blown drivers.

I found an old tiny speaker, hooked it up to the bass driver, and hey presto, sound! Decent sound too. 

So what ever has happened in the past something has blown/damaged the left channel.

Now, where do I get spare drivers from? P/N on the bass is 8480249. Forgot to eyeball the tweeter.

Any suggestions?