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cpc plus 6128 fault

Started by caver99, 20:46, 25 June 24

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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.
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

Bryce

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

Bryce.

eto

Quote from: McArti0 on 09:01, 26 June 24Connect 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

Quote from: andycadley on 10:23, 26 June 24Yeah, 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

Quote from: eto on 10:23, 26 June 24
Quote from: McArti0 on 09:01, 26 June 24Connect 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. 
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

eto

Quote from: McArti0 on 11:52, 26 June 24Therefore, 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
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

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.
CPC 6128, Whole 6128 and Only 6128, with .....
NewPAL v3 for use all 128kB RAM by CRTC as VRAM
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.

Bryce

Quote from: selethomass345 on 08:16, 10 July 24"seeking specialized forums for Amstrad enthusiasts who might offer specific troubleshooting advice."

And what exactly do you think this Forum is??

Bryce.

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