I promise this is the last Midnight Resistance repair log for a while, I have no idea why so many faulty ones have popped up over the last few months, haven't seen any workers for sale anywhere.
Anyway - this board was mint, absobloodylutely mint, could have been made yesterday, not a scratch on it. The only thing I could see that worried me was 2 blacked pins on one of the custom LB0072 custom chips...
...this is a sure sign that something dropped on the board while it was running and shorted these pins out, OR more likely, someone trying to fix the problem jammed their probe between the two pins. When this happens its really a case of luck as to how much damage you can do. If someone is stumbling around probing stuff and they bridge two data pins then this wouldn't do much but if one of those pins was +5V and the bridge gave that a nice easy path to ground then the PSU will gladly step up to the challenge and supply all 15Amps of current at its disposal along that path, until something nominates itself as the fuse and burns out, usually instantly with a puff of smoke and a bad smell, incidentally if you do manage this (we have all done it once or twice) its always useful to postpone panicking or swearing and take notice of where the smoke came from, often a track on the board will have gone from stone cold to red hot and vaporised in a fraction of a second, the burnt out gap can be tiny and hard to spot, so follow the smoke!!! The burnt out section is not likely to be the only fault but at least if you know where you buggered it you can fix it and move on, if you have no idea where it was then its going to be a struggle.
Anyway I had a feeling that the custom was toast and was preparing to have a go at replacing a 160 pin surface mount chip as I have another Data East board as scrap with these ICs on it.
The game booted ok, but some of the gfx were not right.
The in game looks OK but the backgrounds are missing a lot of the colours other than green even tho it actually looks pretty good! Not overly surprising seeing as these LB0072 customs control banks of graphics EPROMs ( I worked out its pinout from a couple of schematics of other games - should doco it for here ).
First step when troubleshooting graphics issues is to check the ROMs, usually they are socketed and its quick and easy, even if it is a bit boring on boards with lots of ROMs. The gfx roms on this board were all mask ROMs, is ROMs that were made with the data already in them, etched in with a photo resist mask that defines the internal structure which defines the data. The were all TC541001P chips, which my reader didn't support, however they are pin for pin compatible with 27C100 EPROMs odd pinout really) so it kinda did support them. Anyway - they all dumped fine except for ROM 9 and ROM 11, both showed up as having blown address pins, #9 was missing 2 pins and #11 was missing 9. Both were ROMs associated with the suspect custom chip.
So I did a check on the board to see if there were any shorts to either ground or 5V on any of the ROM pins, (to make sure the board wasn't going to destroy any chips put into these sockets) burnt new copies of #9 and #11 into a couple of AM27C100 chips using the data from the MAME set, dropped the chips in
and fired her up....fixed!
Am lucky that custom wasn't bad considering the violence it was subject to, surface mount customs are generally very hardy beasts anyway thankfully. Plus it would have been a shame to have to scuff up such a mint board tho I admit I was up for a go.
Right that's my last MidRes board, seriously I don't have any more
