OK, I tried DRAM bank 0 and it was the same as bank 1.
I changed the 16MHz XTAL for a 12.288MHz crystal and it did exactly what I expected. It gave a torn image due to the sync being to slow for the PAL TV.
I used a multi meter on all of the pins of one chip in each bank looking for any shorts. The only pin the was not as I expected was A5 but when I looked at the diagram I see a resistor on this bus pin for some reason. I have assumed one bank is on the left and the other bank is on the right, I don't know if that's true. I tested 16 pins of one chip on the left and 16 pins of one chip on the right which means I have NOT tested the whole 16 pins of the data bus.
So it seem the CPC is booting to a point. Perhaps it sets up the 6845 registers from ROM and then jumps to (Faulty)RAM??? or perhaps faulty ROM
I can't remember if the CPC6128 changes the address space of the ROM through the PAL during boot or if it copies low ROM to high RAM and runs from RAM (disabling ROM). I can't remember ... it's been 20 years since I had one of these.
I haven't changed the electro caps yet. Night here, too dark can't see. Unfortunately the warranty on my eyeballs expire long ago lol. A job for tomorrow.
I looked at this board and though well I could just strip it and start over with new parts but that may NOT be a 'fix'.
Then I though what is the worst and in order they are -
Open circuit via, I will never find it with my sight.
The bigger PAL faulty - I doubt I can get a replacement.
The smaller PAL is more conventional, can I get code for it (Fuse map). Can they still be bought.
I am not worried about the ROMS the code will be out there somewhere.
I doubt I would get the sound chip but I have no reason to believe that it's faulty.
All the other chips I reckon I could still get except perhaps for the MFM MOD/DEMOD that works with the FDC.
I did find another Z80 CPU lying around but it didn't work. It's probably faulty or the wrong type ie NOT CMOS.
Perhaps I should order another CPU ? Do they have to be a particular substrate ie CMOS and NOT TTL or NMOS?
Thanks, Rob.