P38 radio problem

The radio stopped working in my 2001 p38, went crackly on volume then no sound next time I used it, occasionaly came on for about 1 min but not at all recently, It has the harman karden upgrade and built in sat nav model.been looking on ebay for a new head unit as i thought each speaker had a seperate amp but have seen a amp on ebay for a p38?? Range Rover P38 Harman Kardon Radio Amplifier XQK100340 | eBay

does anybody know where this amp should be in the car, and what should i try first?

Thanks all

Forgot to add, that radion lights up fine and appears to work just no sound

Found the amp, and hadit apart and cleaned it :/ it now seems to work intermitantly, on for a few seconds (up to 30 or 40) and off for a few seconds or minuite or 2, cant decide if its a bad connection or a faulty amp any ideas?

Sounds like a dry joint somewhere.