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 revision 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:
I’m currently drawing schematics for the replacement of the HK-1000 and I will post here my results.Stay tuned.
Some days ago I had this Truxton PCB on the bench:
Game had wrong colors on some background/foreground objects, like title screen
This part of graphics is generated by a ceramic PGA custom marked ‘NEC D65081R’ which addresses four 1Mbit MASK ROM and read/write data from/to four 62256 static RAMs:
Address bus is daisy-chained between the custom, the four MASK ROMs and the four RAMs, all was in order here.Custom receives data from MASK ROMs and transmits/receives to/from from RAMs on two different bus.When I went to check connections, I found no continuity between pin 17 (D5) of the RAM @18F and the custom.Here is where trace from pin of the RAM goes under the custom (picture taken with a USB microscope)
Infact, if I pressed the custom in this corner, the fault went away.I simply reflowed this dry joint and all came back to normality.
Today I dumped two PALs from a Big Fight and Ninja Emaki PCBs.In the first board, device was a secured PEEL18Cv8 located on daughterboard @IC56, I was able to fit equations in a GAL18V10 targeting device.In the latter board, device was a secured PAL14H4 @10F on CPU board which I successfully reversed onto a GAL16V8.Both boards had also other PLD devices but all set as registered so not dumpable.