I have a working C128 desktop that I'm using to troubleshoot a non-working C128D-CR.

I suspected a problem with CIA 2 on the C128D, so I swapped its chip labelled "6526A" with a 1988 year stamp with the "6526A-1" from the flat C128 which has a 1986 year stamp. I was expecting these two chips to be interchangeable.

The suspect chip from the C128D failed to boot in the flat C128, thus confirming it is "bad". However, there was no change to the C128D when I installed the known good CIA in it.

SO I am left to wonder if there are TWO faults in the C128D. But before assuming that, I'm also wondering if these two "versions" of the 6526A are actually suppose to be interchangeable?

  • 1
    I can't find a datasheet that gives this as a part number, so its hard to be sure. A lot of people seem to think they work in C64s, but the use there could be different enough to cause issues in a 128, even if they're almost identical chips.
    – Jules
    Oct 8, 2018 at 19:52
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    All I find is original 6526 vs. 6526A, where the "A" means 2 MHz capable. So obviously the C128 needs the "A" part for running FAST mode. But I find no references to "-1", or other revisions, of the "A" part.
    – Brian H
    Oct 8, 2018 at 20:49
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    Could you please clarify what kind of problems were there and what have you suspected exactly? To just check whether CIA problem could prevent the machine to boot, you can patch one of the existing open-source C128 emulators (VICE for example) to have it work without the emulated CIA and see what will happen.
    – lvd
    Oct 10, 2018 at 8:17

1 Answer 1


I have several spare CIAs marked 6526A-1 that I've used interchangeably with 6526A CIAs with no problems.

I cannot point to any official reference but suspect that for some production batches, the labelling was just set up to include the -1 suffix designating revision 1 of the A variant.

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