bear
Well-known member
Two cranky IIxes.
First one doesn't chime (death or otherwise), but rather continually plays random crackly static noises that sound like they are probably the first fraction of a second of one chime or another. ROM SIMM, 030, 68881, sound chip, etc. all okay. Haven't found anything wrong in the ROM/RAM circuitry (yet). Will probably have to check the I/O circuitry next.
Second one wouldn't chime, but would give the chime of death if the SIMMs were removed, or parity SIMMs were installed, so I knew that the RESET and clock circuits were good, plus address/data lines to the ROM SIMM. Isolated and repaired two failed traces in the DRAM control circuit -- one in the address decoder (A21 - UH15 to 68030), the other activating the outputs on the flip flop that controls write enable and selects the correct address lines (UH14 to RP9) -- which brings me to a consistent chime of death (it's progress!).
Here's a schematic diagram of the memory circuitry on the IIx. I traced this out from my boards (and used it to identify the problems on the second board). Maybe it will help somebody.
http://www.typewritten.org/Projects/Apple/gfx/macintosh-iix-memory-copy-outline.svg
FWIW the most likely culprits for rotted traces seem to be between the 68030 (green) and the various 74-series chips (pink), and traces associated with RP9. These are the traces which run the length of the board, or right past (or under!) leaky SMT caps. You can use this diagram to identify if one of them is open-circuit, then you can track it out between vias to find which specific section of that trace is bad. Second most likely culprit seems to be traces terminating at UG11.
First one doesn't chime (death or otherwise), but rather continually plays random crackly static noises that sound like they are probably the first fraction of a second of one chime or another. ROM SIMM, 030, 68881, sound chip, etc. all okay. Haven't found anything wrong in the ROM/RAM circuitry (yet). Will probably have to check the I/O circuitry next.
Second one wouldn't chime, but would give the chime of death if the SIMMs were removed, or parity SIMMs were installed, so I knew that the RESET and clock circuits were good, plus address/data lines to the ROM SIMM. Isolated and repaired two failed traces in the DRAM control circuit -- one in the address decoder (A21 - UH15 to 68030), the other activating the outputs on the flip flop that controls write enable and selects the correct address lines (UH14 to RP9) -- which brings me to a consistent chime of death (it's progress!).
Here's a schematic diagram of the memory circuitry on the IIx. I traced this out from my boards (and used it to identify the problems on the second board). Maybe it will help somebody.
http://www.typewritten.org/Projects/Apple/gfx/macintosh-iix-memory-copy-outline.svg
FWIW the most likely culprits for rotted traces seem to be between the 68030 (green) and the various 74-series chips (pink), and traces associated with RP9. These are the traces which run the length of the board, or right past (or under!) leaky SMT caps. You can use this diagram to identify if one of them is open-circuit, then you can track it out between vias to find which specific section of that trace is bad. Second most likely culprit seems to be traces terminating at UG11.
