[Coco] UK PAL CoCo1 Repair

[Salvador Garcia]

 Huh? I clicked on reply and my reply went directly to R Jones. Sorry about that R!
Here is the reply:
If I understood so far you've checked:
1. All the support logic chips2. The uP3. The uP peripheral chiips4. All voltages5. The RAM chips
Is there a chance that any of the passive components may be damaged? Or perhaps a trace on the motherboard may be open or closed where it shouldn't be?.
Did the CoCo have this same problem before you started working on it? Do you know if anyone else worked on it before you?
>From what you have documenting, it seems you have replaced everything replaceable, short of the mother board.
Salvador

    On Thursday, September 21, 2017, 5:17:46 AM CDT, R Jones <rjones at biketech.org> wrote:  
 
 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.



-- 
Coco mailing list
Coco at maltedmedia.com
https://pairlist5.pair.net/mailman/listinfo/coco