L322 Vogue intermittent sound

Hi, I've got the 2002 Vogue with Sat Nav, BM 54 radio module and Lear DSP amp. When I turn the radio on, the amber light comes on and I get sound for a minute or so then nothing. Turn it off and on again and sound for a bit again. I've swapped out the BM 54 but still the same. Should I change the Lear amp? I'll go for a BMW 740/X5 version as per this forum post.

Thanks, John.

Ignore my earlier comment, you said thanks this time

Replaced the amp and the DVD nav unit but still the same issue. Supplier from the US said it may be the DVD nav unit as seems like the can bus is timing out and amp is turning off. DVD unit initialises the other modules. Stuck now.