This was actually a bootleg PCB, but almost identical to a legit one. It was kind of a pain to work on, since apparently there are no schematics available for the Double Dragon ROM board.
**Symptom #1: Game boots and text appears, but the rest of the screen is yellow with no sprites or background graphics.
- dumped and verified all ROMs in ROMIdent
- probed graphics ROMs with logic analyzer, no action on most address pins of ROMs 17-20
- traced the address inputs through some 74LS273s which appeared fine, to a 74LS245 where most signals were dead
- this 74LS245 interfaces directly with the 2015 SRAM at location A-DD
- all data i/o pins of this RAM were not toggling
- /WE high mostly, /OE low, /CS low, so data should definitely be coming out on i/o pins
- replaced this 2015, graphics are fixed
Solution: Replace 2015 RAM at A-DD on ROM board.
**Symptom #2: During boot, occasionally hangs on 63701 check, or gives 63701 error
- swapped the 63701 IC into a known-good board, works fine
- probed pins of the 63701 with logic analyzer, /HALT signal is always low
- /HALT comes from inverter at IC71 pin 6
- input to this inverter at pin 5 is also low - chip is obviously bad
- replaced it, boots consistently with no errors now
Solution: Replace inverter at IC71 on main board.
**Symptom #3: No sound during game play, but occasionally get random sounds on startup
- suspect digital section due to sounds playing randomly - analog section is likely fine, since random startup sounds are clear and loud
- followed digital path back with logic probe, everything looks fine up to RAM
- piggybacked a new chip onto the 2015 RAM at IC31, sound starts working
Solution: Replace 2015 RAM at IC31 on main board.
Billy and Jimmy are kickin' ass again!
**Symptom #1: Game boots and text appears, but the rest of the screen is yellow with no sprites or background graphics.
- dumped and verified all ROMs in ROMIdent
- probed graphics ROMs with logic analyzer, no action on most address pins of ROMs 17-20
- traced the address inputs through some 74LS273s which appeared fine, to a 74LS245 where most signals were dead
- this 74LS245 interfaces directly with the 2015 SRAM at location A-DD
- all data i/o pins of this RAM were not toggling
- /WE high mostly, /OE low, /CS low, so data should definitely be coming out on i/o pins
- replaced this 2015, graphics are fixed
Solution: Replace 2015 RAM at A-DD on ROM board.
**Symptom #2: During boot, occasionally hangs on 63701 check, or gives 63701 error
- swapped the 63701 IC into a known-good board, works fine
- probed pins of the 63701 with logic analyzer, /HALT signal is always low
- /HALT comes from inverter at IC71 pin 6
- input to this inverter at pin 5 is also low - chip is obviously bad
- replaced it, boots consistently with no errors now
Solution: Replace inverter at IC71 on main board.
**Symptom #3: No sound during game play, but occasionally get random sounds on startup
- suspect digital section due to sounds playing randomly - analog section is likely fine, since random startup sounds are clear and loud
- followed digital path back with logic probe, everything looks fine up to RAM
- piggybacked a new chip onto the 2015 RAM at IC31, sound starts working
Solution: Replace 2015 RAM at IC31 on main board.
Billy and Jimmy are kickin' ass again!
Last edited:

