Thanks Bitmaxz,

That link you have just sent with the 4 steps is getting me somewhere.

Domain is normal at 8.7v so I've gone to step 4 of checking RI voltage (1.8v would be normal)
I have 1.8v on chips 00-31 and 2.2v on chips 32-62.

I suspect chip 32 may be the cause of the fault. Would you agree?