Mac SE error code 00000003 00040000

[gkmaia]

I got this error 00000003 00040000 By looking at Troubleshooting_Your_Macintosh_1992 : The RAM test failed while testing bank B, after passing the chunk tested for code $0002. The Z field indicates which bits failed as in code $0002.

Also the second line shows what bits may have failed. But not sure how read 00040000 and what clue it makes.

I was initially running 4x256kb of RAM I am sure works. Also tried to eliminate bank B by switching the resistor from 35 to 36 and using 2x1MB.

Still the same issue.

 

[SuperSVGA]

I think it's saying that it thinks bit 18 is bad, although I may have my math wrong.

Theoretically setting R36 and putting the SIMMs in bank A (slots furthest from the edge of the board) seems like it should have worked, so I have a feeling someone else is going wrong.

 

[gkmaia]

Yes, that is weird. I removed U12F and 11F as I am getting D9 in the data bus stuck high when compared to a working board. As they were the buffers between processor and memory I thought they could be stuck open. But they are both fine. 

Also the ROM ICs use the data array but I tested them on another working board.  Problem is this schematic is quite incomplete... 

the other weird thing is that Sim 1 bank A and sim 3 bank B use the same buffer. Same for sim 2 and 4. This means this type of fault should be on the sim card, not on the main board. 

So... confusing... not sure.

 

[gkmaia]

WOW spot on! A block of the LS257 failed open, exactly where the bus signal was stuck high. Replaced it and booted just fine!