PCB Repair: Mortal Kombat (T-Unit)


Dead; displays garbage.


I removed and verified program ROMs UJ12 and UG12. Both checksums matched those of the “Mortal Kombat (rev 4.0 T-Unit 02/11/93)” MAME ROMset.

The TMS34010 CPU appeared to be alive, however there was no activity on the /CS lines of UJ12/UG12. The input signal, /PMEMCS, is produced by the TPC-1020A FPGA at UF5.

The FPGA handles address decoding, arbitration between the CPU and DMA2 ASIC and game-specific copy-protection (a unique FPGA is required for each game).


I swapped in an FPGA from MKII, which brought the game somewhat back to life; as far the service mode at least. Bugger. Looks like I’d have to find a working FPGA to progress.

Help was on hand from KLOV forum member esqueleto, who very generously sent me a couple of spare FPGAs. Out of curiosity I tried reading both FPGAs in my Unisite programmer but (shock!) they both appear to be read-protected.

With a new FPGA, the game sprang back into life:

So much blood

I tried setting the blood DIP switch to off but it made no difference. Perhaps something was missing, like blue and green?

The self-test didn’t report any errors with the palette RAM (UA8/UC8), so I immediately suspected the color output latch and/or buffer which handle the blue and green video outputs:

Not everything needs a caption, Phil

Indeed, a quick probing of UB4 showed some incredibly weak outputs:


UB4 was summarily desoldered, replaced and stamped on. All fixed now, right?


What on earth could be wrong now? Referring back to the video output portion of the schematics, there is a 7407 at UA4 which is used to disable each color output during video blanking. Its input, /BLANK_X, originates from the FPGA (aargh) but thankfully it was quite obvious that UA4 was utterly failing at acting as a buffer:

I know that’s a fairly weak input but come on, you’re not even trying…


Replace FPGA at UF5.

Replace 74ALS541 at UB4.

Replace 7407 at UA4.


8 thoughts on “PCB Repair: Mortal Kombat (T-Unit)”

  1. Thanks for this. Had a board showing no green or red, only blue, and very dim. Replacing the 7407 at UA4 did the trick!

  2. Hello,

    I am looking to convert a NBA JAM to MK1 ver5.0 (or MKII but i miss the soundboard).
    Do you have an address where i can find a UF5 chip ?

    Best regards.

      1. Thank you, maybe it’s easier to patch the romset and bypass the security check.

  3. Hello, I am from Argentina and I have 3 MKII T-Unit boards, I would like to know if they can be modified to MKI since it is the same pcb.
    Cheers, Javier..

    1. The FPGA (UF5) is different for each game and acts as a security device. You might be able to modify MK’s code to remove the security checks but I have never looked into it.

      1. I have done it with a NBA JAM T-Unit at address BE518 (maincpu) replace the value CB01 with CB08.

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