I am trying to sort out a 1-2-1 memory error on a Bubbles MPU board. I can't tell you what it is, but I can tell you what it isn't:
(1) It is not the RAM chip. I swapped chip 21 with chip 22, chip 11 and chip 38. The error did not move.
(2) It is not the 74153 chips. I replaced all 4 of them
(3) It is not chip 3H (74LS373) I replacd that chip as well.
(4) It is not the ROM card. I swapped 3 different ROM cards. Same symptoms.
(5) It is not the I/O card. 2 different I/O cards and no I.O card. Same symptoms.
(6) It is not the socket. I checked and all paths show the correct continuity and no stray paths.
Before I start shotgunning chips (worse than I have) I thought I would check to see if anybody else has run into this on any other Williams MPU boards and has any hints.
Also about once every 10 boots it comes up without the RAM error. If I warm reboot it (via reset switch), it will occasionally show a 1-3-1 error.
ken
(1) It is not the RAM chip. I swapped chip 21 with chip 22, chip 11 and chip 38. The error did not move.
(2) It is not the 74153 chips. I replaced all 4 of them
(3) It is not chip 3H (74LS373) I replacd that chip as well.
(4) It is not the ROM card. I swapped 3 different ROM cards. Same symptoms.
(5) It is not the I/O card. 2 different I/O cards and no I.O card. Same symptoms.
(6) It is not the socket. I checked and all paths show the correct continuity and no stray paths.
Before I start shotgunning chips (worse than I have) I thought I would check to see if anybody else has run into this on any other Williams MPU boards and has any hints.
Also about once every 10 boots it comes up without the RAM error. If I warm reboot it (via reset switch), it will occasionally show a 1-3-1 error.
ken
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