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Sad Mac (Plus, Rev 2 ROM)

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Thought it would be better to have a separate topic so anyone finding this by search/Google could see it more easily.


I installed four 9-chip, 30-pin 1MB SIMMs into my newly built Plus, and when it boots upon performing its RAM test, I get a Sad Mac code 030ff0.  Googling around indicates the first byte (03) indicates a memory failure, and the latter two bytes indicate which chip failed, although since it's a set of SIMMs that isn't a terribly helpful number.  I have several sets of this type of RAM laying around and I've tried different combinations and it doesn't work.


Occasionally, the error offset may change to something like 030400, but that's still a memory failure error code.


Resistors R8 and R9 are clipped and pulled aside to enable detection of high-density SIMMs.  I'm going to try resoldering it and installing four 256K SIMMs to see if that fixes the issue.  The board has been cleaned on a hot (no-detergent) dishwasher cycle as of two weeks ago and no shorts, scratches, or defects are otherwise visible.


Note that the board arrived with the resistors already clipped, so I have never seen the machine boot with any different RAM configurations.


I'm making this thread mainly to ask if there is anything else I can try, any chips I should inspect for faults, and if there are particular types of SIMMs that I should look for in the future to mitigate this kind of problem.  I've read things about ECC and non-ECC RAM but I don't know enough about RAM to know one way or the other.

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Okay, confirming here that installing four 256K SIMMs and replacing R8 did, in fact, permit it to boot, indicating this is an issue with the RAM I was using.


All of these RAM sticks have tested good in the past using an old build of memtest on a 486 motherboard, so it's not necessarily that they are bad sticks, but maybe because of parity, timing, or ECC.


EDIT: It turns out, one of the SIMMs was indeed bad.  Per recommendation of users in IRC, testing in a 2.5MB configuration to narrow down the bad SIMMs one at a time has isolated the bad stick.  I have procured another 4MB set and they all test OK.  The Plus boots.  Thanks for reading.

Edited by sigtau
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