Fixing my C128D

[PhilC]

@rubber_jonnie There are pull-ups but I've checked all of those with the power off and they all pull up to 5V when pressing reset.

Ahh well, worth a go.

It certainly was. The only other thing in that region of the address bus is the PLA, so hoping that's not failed too.

[rubber_jonnie]

Ahh well, worth a go.

It certainly was. The only other thing in that region of the address bus is the PLA, so hoping that's not failed too.

PLA would be bad news...

[PhilC]

Did a bit more scoping and testing of the roms. The roms all read fine into my TL866 so I'm going to rule them out at least for now.

I removed the PLA to socket it like the rest of the large chips and thought what the heck, lets see what the address bus does with it removed and unfortunately, it looks like the PLA has also gone pop as the address lines pull-up, then pulse for a second or two and then go to 0V which they didn't before.

I'm really hoping this is the end of the chip purchases for this C128D as its been pretty expensive so far.

[rubber_jonnie]

Did a bit more scoping and testing of the roms. The roms all read fine into my TL866 so I'm going to rule them out at least for now.

I removed the PLA to socket it like the rest of the large chips and thought what the heck, lets see what the address bus does with it removed and unfortunately, it looks like the PLA has also gone pop as the address lines pull-up, then pulse for a second or two and then go to 0V which they didn't before.

I'm really hoping this is the end of the chip purchases for this C128D as its been pretty expensive so far.

Well it's good that you have a possible culprit, not so good it's the PLA. Is it a C128 specific one, or standard C64 PLA?

[stephen_usher]

It's not the same as the C64.

There is a modern replacement but it's from the USA and would be mega expensive unfortunately.

[PhilC]

It's not the same as the C64.

There is a modern replacement but it's from the USA and would be mega expensive unfortunately.

I did see that but fortunately I found a seller on eBay with them, so I’ve bought 3 of them, one for this C128 and the other two for stock should I ever need to fix another one.

Ironically the only chip I purchased that I haven’t needed is the VIC - II but it’s good to have spares if all the big chips.

[rubber_jonnie]

It's not the same as the C64.

There is a modern replacement but it's from the USA and would be mega expensive unfortunately.

I did see that but fortunately I found a seller on eBay with them, so I’ve bought 3 of them, one for this C128 and the other two for stock should I ever need to fix another one.

Ironically the only chip I purchased that I haven’t needed is the VIC - II but it’s good to have spares if all the big chips.

Yeah, spares are becoming a bit of an issue, and whilst there are some good solutions out there, they don't cover every chip we might need. Good to have some stock.

[PhilC]

Really quick delivery from the EBay seller and the PLA chips arrived yesterday but I was out all day as it was the grandsons birthday.

Got a bit of DIY to do and then later on I’m hoping to power up the C128D with the new PLA fitted and see what happens.

[rubber_jonnie]

Really quick delivery from the EBay seller and the PLA chips arrived yesterday but I was out all day as it was the grandsons birthday.

Got a bit of DIY to do and then later on I’m hoping to power up the C128D with the new PLA fitted and see what happens.

Keeping my fingers crossed :)

[stephen_usher]

Same here