Posted By
MMS
on 2021-09-24
01:39:02
 |  Re: Help troubleshooting
If you check out the content, it is evident, that those characters are not valid ones.
So I see three options:
1) really the content decoding is wrong, and the CPU has troubles.
I think this is the most expensive exchange, so maybe it should be the last step to swap the CPU.
2) the ROM is damaged, and it contains now random values, including charset, or the startup code
Maybe it is worth to try to swap the ROM (s) (MCes has some modern, low power replacements) as from a damaged ROM inside the machine it cannot run it's own microcode.
3) as not only the charset is damaged, but instead of the initial startup places (on the top os the screen) the full screen has random values, some of the lower RAMs could be dead (too), where the screen and color memory exist, even the zero page with so many important system values.
RAMs typically soldered inside, so I would not replace them, but there is an option to get some 41464 chips and try to piggyback the suspected one temporarily. (sorry, maybe the type is not correct, it could be for the 64K version, but I do not know by heart the 16K RAM chips)
https://www.youtube.com/watch?v=mxhEgmG6vh4
If it cures the issue, then you found the defective RAM chip.
There are several options to change the internal RAM chips, and may do the 64K upgrade at the same time. including the Lotharek CPU swap contains 256KB SRAM next to the new CPU, MCes has a 64KB upgrade put the extra RAM under the TED IC, very elegant method
This one is also nice:
https://www.youtube.com/watch?v=5dnHICcseGI
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