Testing shows databit 10 is always stuck high on commodore amiga expansion

With help from Ralf on this comment I was able to

  1. Disable the memory by no-longer grounding PIN 32, and sometimes forcing CE high on the SRAM chip.
  2. Boot a workbench disk, and then break it on startup.
  3. Insert a disk containing addmem from ykick and memtest.
  4. Re-enable the commodore amiga A501 replacement prototype.
  5. Run “addmem $c00000 $c7fffe”
  6. Then, run memtest.

As you can see (and this is true over a large number of errors), databit 10 is always stuck high.

I’ve got to figure out why this is……..this doesn’t go through any latches or logic on my board.



Amateur Electronics Design Engineer and Hacker


  • The theory was that either there was a wiring problem (which there isn’t) or the chip had a minor soldering flaw. I re-soldered the chip, and we still have the same problem. Time to do a new chip!

  • Soldered a new chip onto a new surfboard, plugged it in, same exact problem as before.

    Pulled off the connector to the motherboard, sprayed some contact cleaner, and now the amiga boots sometimes and recognizes the memory……

    we’re getting there.