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Thread: Mos 6526.

  1. #1

    Default Mos 6526.

    Dear All,

    I have a working C128 and a C128D and in both the di tells me both CIAs are dead. I tried the CIAs of a not working C64C and they are both told to be bad.
    Possibile situations:
    . Murphy is laughing
    . "something" is causing false positives
    . the testing tool is not working only with these two C128

    Some help / suggestions?

  2. #2


    Get a good 128 test tool. Or test CIAs on a C64 with a known good tool:

    Frank IZ8DWF

  3. #3


    Now I think I have understood... it's the testing tool! or I am not so good at using it (never had an issue before... perhaps it is "sick"...).
    This afternoon I left home with BAD CIAs and SID!!! i was "many different adjectives"...
    After dinner I decided to try again and, while in the afternoon I was using only the main cartridge, I decided to connect everything and, MAGIC!, only one CIA, u4, is BAD.
    I tried to invert the two CIAs and u4 is still BAD.

    I then decided to use only the cartridge on a working C128D (or at least a one that never gave me a problem) and... the two CIAs and the SID are reported as bad.

    At worst now I have a way to test a C128! With the issue that I have then to invert the two CIAs...

    This is the screen only using the cartridge:

    This is the screen using everything:

    This is the main cartridge:

    This is everything connected:

    I am sure I have pressed the "right" buttons on the testing HW... on the main cartridge I am sure since the button selects the type of diag program (C128 or C64 mode).
    Now I have a doubt about the user port...


    Does anybody knows this type of testing HW and give me some hints?
    Attached Images Attached Images

  4. #4


    Ok. Found the issue. Ok that the testing tool must be completely connected. And ok that the user port WAS a bit oxidated.


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