cpc plus 6128 fault

[caver99]

amstrad 6128 plus

i have an issue with the 6128, hopefully this pic is viewable

would anyone have any ideas on what to look at first?

20240625_195744.jpg (dropbox.com)

[caver99]

sorry the link didnt work, ive managed to shrink the picture down to fit now.

[McArti0]

Connect the ROMDIS line to 5v. The image should change to vertical stripes. Although I don't know if something else is needed in the case of Plus.

[Bryce]

Assuming that you have a working cartridge inserted, the RAM seems to be bad.

Bryce.

[eto]

Connect the ROMDIS line to 5v.

I might be wrong but I think that unlike the CPC the Plus will not read from Cartridge at all when ROMDIS is set, so it won't be able to initialise and I would expect no output at all.

[andycadley]

Yeah, it's managing to set up the border ok so I'd be inclined to suspect bad RAM over anything else.

[eto]

Yeah, it's managing to set up the border ok

Border and CRTC logic are set-up correctly and the pattern clearly changes every 64 characters. That's afaik a typical sign for a fault in the RAM logic as the ROM started successfully.

Hopefully just one of the RAM ICs and not the logic inside the ASIC (but I guess an error there would come with more/other issues). 

[McArti0]

Connect the ROMDIS line to 5v.

I might be wrong but I think that unlike the CPC the Plus will not read from Cartridge at all when ROMDIS is set, so it won't be able to initialise and I would expect no output at all.

Therefore, the ROMDIS trick should be implemented after turning on CPC, not before.

I saw such a screen on a full working CPC6128 computer when it was turned off ROM. 

[eto]

Therefore, the ROMDIS trick should be implemented after turning on CPC, not before.

can you explain what will happen if the computer is already in this state and then you switch on ROMDIS?

[McArti0]

Z80 starts executing program from RAM Which quite quickly ends with the RAM being filled by the stack. Z80 enters the FF RST 38h trap and does not escape until it fills the RAM with address 0039h

[McArti0]

@eto
And what is obvious, when z80 reads from a ROM disabled via ROMDIS and enabled via RMR (Lower ROM enabled), it will always read the FF RST 38h command. And he's trapped.

[selethomass345]

Hi,
I think you should facing this issues with your Amstrad 6128 Plus, sharing a clear picture of the problem can help others diagnose it. Look for responses that suggest checking connections  inspecting internal components like chips or connectors or seeking specialized forums for Amstrad enthusiasts who might offer specific troubleshooting advice.

Thanks

[Bryce]

"seeking specialized forums for Amstrad enthusiasts who might offer specific troubleshooting advice."

And what exactly do you think this Forum is??

Bryce.