new T-unit/Wolf-unit repair tales :)

mecha

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short version:

Mortal Kombat 2 (single board model with 8 megabit roms) (also applicable to just about any board too though I guess)
problem: testing known good roms in rom sockets showing bad
solution: check continuity between the same pins on the adjacent sockets. if one (or more) shows dead, jumper that pin to the same one on the next socket, should fix it. :)

Ultimate Mortal Kombat 3
problem: no sound (Sound Chip U1 Not Responding error); game runs horribly slow/sluggish inputs
solution: U57 chip may be bad. replace with known good one (if you can find one). as a custom programmed PAL chip, you would have to snatch this from another Wolf-unit board.

tl;dr version:

Mortal Kombat 2 (single board with 8 megabit roms) -- good roms showing bad
back in November I happened to get this bright idea of buying non-working boards with the hopes of fixing them. now it's not anything like what say channelmanic or RetroHacker would do, but they're repairs nonetheless, and they helped me understand a little bit more about these Midway boards..

the first was a single board variant Mortal Kombat 2. for whatever reason (I know the reason now lol) the UG22 rom was pulled from it, so before I could proceed any further with it I reprogrammed a rom from a non-working UMK3 to replace it and the rom still showed bad in the power on test.

the board also had some graphical issues, notably the blocky/distorted text, which is typically caused by some kind of problem with the graphics processor. my first approach was to just give the board a bath, and I noticed some fluxy/solderlike goo spread across some traces going to the DMA controller, so I scraped that mess off. I inspected the backside for bent/touching pins several times and came up with nothing. I still trimmed a bunch of them anyway, if not all, I can't really remember having worked with 2 other T-unit boards at the same time.

when that turned up dry, I simply swapped the roms/graphics chips between it and another NBA Jam board I had. the single board MK2 roms will not read in any other T-unit board unless you move the jumpers between the game roms and graphic roms. what I found intriguing though was that NBA Jam's roms were actually reading on the MK2 board, and roms UG22 and UG23 were showing bad, when I know they were both good.

taking a tip given to me by channelmanic when I was fixing my Smash TV board, I used my meter to check continuity between same pins on the socket before UG22 (which I think is UG20?) and found one showing dead. I confirmed against other sockets and boards and sure enough, they all need to connect. I started trying to desolder the socket like an idiot though to get at the traces beneath, but aborted that mission and instead ran a small insulated (key word) jumper wire between the pins and voila, now all the rom sockets work again. the graphical glitches were not caused by the graphics processor or any hardware on the board, it was instead caused by the non-working rom sockets.

if anyone has a MK2 sound board they'd like to donate... ;) (cabling not required)

Ultimate Mortal Kombat 3
this board was an absolute mess. I purchased this and another one in non-working condition thinking it was be easy fixes. I suppose it was, if only I had the right parts to do it. first off, the graphics processors (U45 and U47) were both nuked on both boards. I stole the graphics chips from my personal UMK3 board just for testing and I got a picture to come up but was greeted by some error I'd never seen, which I believe said "Sound Chip Bad U1 Not Responding", after which the game would run, but it ran at like half the speed and most of the buttons were non-responsive, especially in test mode, for whatever reason only the Block button can access menus.

I bought replacement graphics chips off ebay, I went for the cheaper ones and they arrived to me non-working. so I shelved this. until tonight, I wanted to try something else. I initially thought the U1 surface mount chip may have popped a solder joint, cause the board itself looked like it had a flex in it. after checking continuity between chip legs and the adjoining capacitors, they all were fine. I looked to another place the traces were going though, the U57 chip that not even the MAME people know what it does... I've alluded to a "sound chip" over the years on here, and well, I think I found it.

when that chip is bad, the sound processor lacks the software to drive it, Broodwich was kind enough to share what it was, and it's exactly that, the software driver for the sound hardware. don't ask me how I knew this, I tried tinkering with the other UMK3 board for awhile too, I never got it to boot up or anything, but it did play the end round music for the Subway, so I just guessed I had a good donor U57 from it.

it worked. now once I get new graphics processors, I think I have some boards to sell.
 
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