DarrenF
Well-known member
Working on a dead 1942.
Lots of nice tile/character/sprite garbage on screen when powered on. This tells me the video section is more-or-less working. However, there's no movement or change, it's not "booting".
Inspected for physical damage; none found.
Voltage is good (5.0-5.1) all over both boards.
Pulled & verified all of the non-gfx EPROMs; they're all good.
Checked continuity of all lines in the interconnect cables; good.
Probing both Z80s: the reset lines are staying high; the clocks are pulsing; there is activity on all data lines and most address lines. Only thing curious to me is that the INT (not NMI) line is staying low.
I also noted that the RAMs (TMM2016s) are hot. Measured them at ~150°F. It's hot enough that if I touch them wile probing around, I pull away by reflex. It's uncomfortable to touch for more than a couple seconds, but it's not going to give you burns or anything.
Anyhow, it's a real pain for me to diagnose, as I can't find any schematics for 1942. The best I can do is look at schematics for similar era Capcom games and hope they did things similarly. So I've been looking at the GnG and Commando schems for clues. I suppose it's better then nothing, but it still sucks.
So, anyone have any sage advice? Does that RAM sound likely bad? Or would you try chasing down whatever's pulling the INT line low? Anyone ever run across the schems for 1942? Anyone drawn their own by tracing the circuitry? (Cause I'm about to try...)
Lots of nice tile/character/sprite garbage on screen when powered on. This tells me the video section is more-or-less working. However, there's no movement or change, it's not "booting".
Inspected for physical damage; none found.
Voltage is good (5.0-5.1) all over both boards.
Pulled & verified all of the non-gfx EPROMs; they're all good.
Checked continuity of all lines in the interconnect cables; good.
Probing both Z80s: the reset lines are staying high; the clocks are pulsing; there is activity on all data lines and most address lines. Only thing curious to me is that the INT (not NMI) line is staying low.
I also noted that the RAMs (TMM2016s) are hot. Measured them at ~150°F. It's hot enough that if I touch them wile probing around, I pull away by reflex. It's uncomfortable to touch for more than a couple seconds, but it's not going to give you burns or anything.
Anyhow, it's a real pain for me to diagnose, as I can't find any schematics for 1942. The best I can do is look at schematics for similar era Capcom games and hope they did things similarly. So I've been looking at the GnG and Commando schems for clues. I suppose it's better then nothing, but it still sucks.
So, anyone have any sage advice? Does that RAM sound likely bad? Or would you try chasing down whatever's pulling the INT line low? Anyone ever run across the schems for 1942? Anyone drawn their own by tracing the circuitry? (Cause I'm about to try...)

