Professional software development, amateur BMW tinkering, old arcade game stuff


Taito Chase HQ arcade pcb repair

Initially a completely dead board, with no clock signal at the CPU.  Some probing revealed the crystal oscillator didn’t have any power going to it, and in fact nothing on the top board had +5V.  There was a very unusual broken trace on the main +5V line from the edge connector, and a handful of capacitors that had pretty much came apart.

IMG_4239 IMG_4235

With that fixed the board booted to a lot of garbage graphics – no sprites and no road layer.


The road layer is handled by the top board – pretty much the custom chip, two RAM chips, a ROM and a PROM (the other two RAM chips in that corner are the palette RAM).  In this case the 63s141N PROM had failed and had dead outputs.  A PROM was taken from another board and the road layer fixed.


The title screen had some interesting sprite behaviour – the first entry in the sprite list seemed to be drawing somewhat correctly (The ‘CH’ of the Chase HQ logo).  That made me wonder if some kind of counter had failed and it was only processing the very first address of sprite RAM over and over.  There are a bunch of LS161 counter chips on the video board and there was a dead input on some of them.  This traced back to a PAL chip which was replaced by one from another board and all sprites displayed, albeit with a lot of garbage and vertical line corruption.

IMG_4266 IMG_4325

The final part of the puzzle are the 16 sprite work RAM chips on the video board – if any of these fail it will tend to be vertical lines or other corruption throughout the screen.  The sprite RAM seems to be in ‘screen space’ – so faults don’t follow the sprites but instead have constant positions on the screen.  On this board 5 chips were confirmed as bad and when replaced the board was 100% again!

IMG_4326 IMG_4271


IMG_4295    IMG_4286 IMG_4284


2 Responses to Taito Chase HQ arcade pcb repair

  1. Paul says:

    Hi really impressed with your ability to fix these boards. I have an two sets of SCI boards which I believe is based on the same system z boards for Chase HQ, but it does seem to be laid out different.
    Both video boards have a similar garphics issue with vertical lines, which searching the net it was suggested it could be the SRAM on the video board.
    One CPU board again has the same issue with no road or car showing and the other CPU board just boots to garbage and probing the 68000 they just go through a reset cycle every few seconds.
    Looks like I have a challenge ahead to try and get these sorted so appreciate what you have done and am trying to use that as a guide.

    Have you done any SCI boards? Any tips also appreciated.

    Thanks and keep up the good work.

    • bmcphail says:

      I’ve actually got an SCI board myself I haven’t fixed yet – the CPUs just constantly reset and it doesn’t even get far enough to display anything. I’ll put some time into fixing it eventually.

      If the vertical lines are in ‘screen space’ (they don’t move with the sprites) then it’s probably the RAM on the lower board. If the lines move with the sprites, it’s probably the sprite mask ROMs that have failed.

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