Double Dragon PCB repair log

delroy666

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Donor 2011
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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!
 
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I got that Scan from Lord Nightmare over at the Mameworld forums. I'm sure with some sweet talking, he'd probably scan the ROM board too.

I followed your lead and went over to the mameworld forums and did a search for 'Double Dragon schematics'. Someone posted complete (and cleaner) scans of the schematics for both boards not even a year ago:

http://www.mameworld.info/ubbthread...ews&Number=238772&Forum=All_Forums#Post238772

Guess those forums aren't indexed by Google. Don't know why I didn't think to look there before. Thank you! :cool:
 
I have a bootleg PCB with a yellow screen also. These logs are really helpful.
 
Wow - thanks for the links for the video board schematics, I googled my arse off a few months ago for then and found nothing.
 
Nice job with the repair! My Double Dragon is running a bootleg board too and it also looks very similar to a legit board. I've noticed it is more picky than other legit JAMMA boards in terms of the video output...say I have the monitor dialed in for that bootleg board, then other legit boards look way too dark. I've been thinking of buying a legit Double Dragon board just so the monitor looks better swapping between boards.
 
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