[R-390] Field changes for CV-591a / MSR4

[Robin Filby]

All.
 
I have recently acquired a CV-591a unit and there is a sticker on the front panel which indicates
that field changes 1,2,4,5 & 6 have been actioned.
Can anybody advise me of what these field changes are and even better point me in the direction
of where I can find complete technical copies of these changes.
 
Thanks.
 
Rob.