Some months ago I received for a repair this Tatsujin Oh PCB (known outside Japan as Truxton II)

As you can see from the above picture, the custom ‘HK-1000’ (used for inputs) in front of JAMMA edge was missing but this was not the main problem, board won’t sync up:

All the graphics and video timing signal (HSYNC, VSYNC, etc..) are generated by a large surface mounted ASIC (208 pins QFP package) marked ‘GP9001’:

You can find its pinout on page 32 of the Knuckle Bash schematics:

https://www.jammarcade.net/files/Schematics/Arcade/Knuckle%20Bash.pdf

The IC was previously reworked by someone in a bad way, many pins were bridged together, flux residuals were not cleaned.So I decided to remove it :

and solder it again:

Happy with the result I powered up the board again and I was greeted but this static garbage screen:

Probing the main 68000 CPU revealed no activity on data bus.Doing a visual inspection of PCB I found a couple of severed traces on solderside just around the CPU area:

Patching them allowed the board to boot but, obviously, due the lack of the ‘HK-1000’, the game was stuck on a ‘TILT’ error message:

Input check in TEST mode reported ON most of them  :

Now some words on the ‘HK-1000’.As said, this custom handles all inputs and it’s has been adopted in later Toaplan PCBs.There are two revisions of it, the early one has a ceramic package and due this nature it’s very prone to damage and failure.This revision is used on Truxton II/Tatsujin Oh and FixEight:

The newer revision is more robust and it’s used on Ghox, Pipi & Bibis:

Back to repair, from available info it seems the functions of this custom can be reproduced using a couple of 74LS240  (actually the custom handles also the coin counters and lockout but we can omit it), this is not a suprise for me since a lot of previous Toaplan boards use same design with these TTLs (see for example Truxton, Wardner, Hellfire and other).Doing some tests with a single 74LS240 I was able to successfully map some inputs turning off the TILT error

This allowed me to enter in game :

Later, owner of the board installed the missing HK-1000 and confirmed the board was perfectly working after my repair:

P.S.

I’m currently drawing schematics for the replacement of the HK-1000 and I will post here my results.Stay tuned.

Got this rare Big Fight – Big Trouble In The Atlantic Ocean (this is the full title) PCB for a repair :

For the uninitiated game a beat ’em up which resembls Final Fight but it features also a versus mode.It was developed and published by the obscure Tatsumi manufacturer in 1992, it was one of their last arcade game before focusing on novelty sticker printing business.

The board was completely dead, I got only a black screen.The hardware is complex : two 68000 CPU, a large PGA sprites custom IC, many PLDs, lots of RAMs.Here is picture with the daughterboard removed:

Probing the two 68000 revealed no clock, master clock is generated by a 50MHz oscillator and then divided by 4 in order to route a signal of 12MHz to both CPUs:

The output of the oscillator was dead, stuck at 1.64V  :

I removed it and the its VCC pin was stuck on PCB detached from the package due rust corrosion:

Fitted a good oscillator and board sprang to life although with bad graphics:

Doing a visual inspection I found four empy sockets, according to the MAME source PCB layout and pictures on the Net they had to accomodate four TC51832 32K x 8-bit pseudo-static RAMs besides the other four present:

Once fitted the four missing RAMs most of graphics were correctly displayed but sprites were absent :

The sprites are generated by the PGA custom ‘TZB315’ (see picture above) so I went to probe the surrounding area and found discrepancies between inputs and outputs of some 74ALS245 which are in the middle of ROMs and custom data bus:

I replaced them and, although they resulted good when tested out-of-circuit, I got sprites back although scrambled  :

Sprites data are stored in eight 4Mbit 32 pin EPROMs:

I dumped them and they matched the MAME ROM set but I noticed some of them had oxidized legs:

I cleaned them and at same time replaced a device with a dodgy pin:

This fully restored sprites:

But as you can see (or better, hear..) in the above video, sound was sometimes noisy and some voice samples were missing (like helicopter when you start a game or voice of special moves and enemies).

Here a recording from a working PCB for comparison:

The background noise was due a dirty 50KOhm potentiometer, I removed and sprayed it with a contact claner :

Voice data are stored in a 2Mbit EPROM and played by an OKI MSM6295 (corean rebadged one on this PCB)

The dump of the EPROM was good, I also replaced the OKI with no luck.Probing the EPROM revealed that pin 30 (address line A17) was always LOW so the second half of the voice data could be not accessed.Doing a check with my multimeter revealed thas this pin was tied to pin 22 (/CE), this obvioulsy sounded me weird.Near the EPROM there was a jumper installed @JP4:

Looking at PCB pictures on the net I had confirm that the jumper had to be set in this configuration.But looking at its solderside I noticed a trace which connected  the central pad to the left one.This obviously, along with the jumper installed in that position, caused the short between the left and right pad resulting the two signals being tied together.So, I cutted this trace:

This restored the missing voice samples.No further issues were found so board 100% working.