604n not detected

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Don't Panic. Please wash hands.
  • I recently aquired an A600 revision 2D - Naturally I decided it needed some love ;-)


    I purchased an A604n ram expansion, but I am having problems getting it to be detected - it keeps insisting it only has 1mb ram :-(

    As all the units are tested before leaving Individual Computers, I am currently blaming the A600. Question is what could be the issue ?


    I did a recap of the board (much needed), and I cleaned the ram expansion connector with a pensil-eraser, but the problem persists (nothing but the 604n is connected to the A600).

    I'm open to any suggestions as to what to probe/test to debug this A600.

  • If the computer itself runs, I'd probe the memory with HRTmon, C-Mon or Megamon; it should be available at $0010.0000 to $001f.ffff. Fill the area with some test patterns first (all-00, then all-ff, then $55/$aa) and see if there's any errors.


    What version of the A604n is it? There's one with a bigger square logic chip and SD-Ram reaching under the Indivision socket, and another that only has a D-Ram memory chip and a tiny 14-pin logic chip (current version).

  • Thanks for the suggestion - I went ahead and tested a few memory locations using hrtmon.


    The memory is definetly there however it seems to not be working as expected - as far as I can tell bit 8 has an issue (lowest bit of highest byte in 16bit access). I.e. if I write #$7171 into an address and read it back then I get #$7071.

    This seems to happen for all the (even) addresses I tried between $10000 and $1ffff.


    When I get a moment then I'll sit down with the multimeter and check for continuity to pin 14 on the expansion slot.


    I figured that this would also be the reason that the memory was not detected, as it is my understanding that chip-ram detection is done via exec writing bytes to and from the ram to see what is there.

    However I went and checked the disassembly of the exec v1.2 that can be found online, and as I can tell they use the probe value #$F2D4B698 i.e. they specifically do not set bit 8. So maybe something else is also the issue regarding detection.


    The 604n is brand new, only removed from the packaging to insert for these tests - it's the version with the 14pin logic chip (604n rev2 ?)

  • The newer Kickstart of yopur A600 might use a different probe value (even multiple ones), as using a single proble value is no good for memory detection.


    Let's see what your multimeter probing reveals. While you're at it, you might also give the solder joints of the A604n RAM chip an extra visual inspection.

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