Stripped down head unit
gIzzE, makkan00 and Frobious,
I found some time and completely stripped my head unit down into as many pieces as possible. And I found what was damaged. One of the Chips on the power board had burnt out and left a burn mark on the Chip and heat sink.
The strip down is very fiddly but as long as you take your time its not a difficult job just a bit intimidating.
Any gIzzE sent me a salvaged head unit carcass so I swapped the power board and rebuilt the unit.
Hey presto the sound is back. All channels are working but I think the original head unit was coded as HiFi because output voltage is low and without an amp you would not hear the sound.
What is peculiar is, the music, satnav and phone volumes are fine but as i was working the low battery warn alarm went and it was really loud. The ice warning is very loud as well.
Hopefully the attached pictures will help anyone who has to strip their heads down.