[Coco] UK PAL CoCo1 Repair

[R Jones]

Thanks for the reply.

I have checked the voltages at the ICs and they all check out fine.

This is a 32K machine with the  64Kb ram chips. I removed the ram and 
checked the voltages on the sockets:

RAM jumper on 16K
pin1 -4.8
pin8 12.0v
pin9 5.1v
pin16 gnd 0v

RAM jumper on 64K
pin1 +5.1v this is nc on the 64Kb chips
pin8 +5.1v
pin9 a7 line, pulses ~4.5v high
pin16 gnd 0v

The ICs, components and test points are all numbered differently on this 
board to those in the reference manual. Although I have checked the 
supply voltage with the datasheets and all ICs are receiving the correct 
supply voltages and ground.

I have bought 2 new sets of ram along with another supposed working set 
from another coco which I was given some time ago. I have rotated all 
these chips one at at time and sets at a time and it makes no difference 
to the output on screen.