Fixing my C128D

[PhilC]

@rubber_jonnie I've got a dead test cart but they assume that the CPU is working to be able to function, ie detecting faulty ram chips (which they are very good at) This C128D doesn't get as far as that so the cartridge does nothing unfortunately.

[rubber_jonnie]

@rubber_jonnie I've got a dead test cart but they assume that the CPU is working to be able to function, ie detecting faulty ram chips (which they are very good at) This C128D doesn't get as far as that so the cartridge does nothing unfortunately.

Rats...

Out of curiosity, is anything socketed or is it all soldered?

[PhilC]

@rubber_jonnie Only chips that are socketed are the Roms, SID, VDCs and a couple of the other large MOS chips.

IMG_2812.jpeg

[rubber_jonnie]

@rubber_jonnie Only chips that are socketed are the Roms, SID, VDCs and a couple of the other large MOS chips.

IMG_2812.jpeg

Have you tried removing the socketed chips one at a time to see if anything changes on the address bus? BTW are you getting a CE signal to the ROMs?

[rubber_jonnie]

I was just doing some digging and saw that the machine starts in Z80 mode and then hands off to the 8502, so can you see what the Z80 is doing on boot?


Also, are you able to blind type GO 64 and hit enter to see if it swaps modes?

[mrbombermillzy]

Again, my C128 days were quite a while back, but IIRC, if you put the CP/M disk in the drive and switch on, it will autoboot before the Z80 gives up the machine to the 8502. (Jon just reminded me of this with his above post). :)

Maybe try that?

[PhilC]

Again, my C128 days were quite a while back, but IIRC, if you put the CP/M disk in the drive and switch on, it will autoboot before the Z80 gives up the machine to the 8502. (Jon just reminded me of this with his above post). :)

Maybe try that?

Actually that's not a bad suggestion, after I've socketed the two chips I'll give that a go.

[PhilC]

Okay, so not a great deal of timer today to carry on with the C128 but have tried a few things.

I found some bad corrosion on a couple of the Z80 pins, they looked like they were connected to the PCB track but looking at the at a different angle I spotted they had corroded away. So fixed them but still no boot :lol:

I've checked the ROMS OE CS and CE and two rooms are set to work but two are held high on OE, that will probably tell me which stage its got to in its start up hopefully, so got some googling to do.

[rubber_jonnie]

Again, my C128 days were quite a while back, but IIRC, if you put the CP/M disk in the drive and switch on, it will autoboot before the Z80 gives up the machine to the 8502. (Jon just reminded me of this with his above post). :)

Maybe try that?

Actually that's not a bad suggestion, after I've socketed the two chips I'll give that a go.

Sounds like we have an accord :)

[mrbombermillzy]

Sounds like we have an accord :)

Indeed. :)

It probably needs at least three of us to diagnose a machine with 2 different CPUs and 2 different video chips! :lol: