Carnival

ByMichael Coates

Carnival on a Gremlin / Sega Vic Dual PCB.

Just had blue bars on screen, although probing the Z80 showed it was trying to run code.

Using a logic probe I discovered that the /WRITE signal of the ram chips was always high. This signal comes from a 74LS10 at U77. Checked this chip and one of the inputs – WG (pin 4) was always low, so the NAND output was always high. WG signal is generated from the 74LS175 at U19 and sure enough, Q and /Q were static.

Replacing this chip returned the write signal to normal, and fixed the game.

Similar Posts

  • Do Run Run

    ByMichael Coates

    Crashing game. Game woud start attract mode, but shortly after would crash and boot loop. Entering test mode (hold player 1 start button whilst switching on) and it would pass first time around, but fail at random addresses on subsequent runs. The /WAIT signal on the main Z80 is handled by the IC at E2…

  • Hantarex MTC9000/A

    Byadmin

    No picture, Hole blown through LOPT. Had problems tracking down replacement – little tip given to me by Hantarex engineer – you can use the LOPT from an MTC9000 as long as you cut pin 2 off. (If you leave it connected, you will get a direct short to GND)

  • Gallag

    ByMichael Coates

    Ran through self test OK, came up with chequer board screen and then reset most of the time. Occasionally would start game, but with credit noise continually playing and credits rapidly counting upwards. This is caused by CPU 4 (E5) not running properly. checked the eprom and ram (C5,D5 and E5) and ram was faulty….

  • The Invaders – Zaccaria

    Byadmin

    Totally dead, no screen display (blank white screen).  For this I used the Fluke Z80-S2650 adapter to check out the ram and rom, and located two errors. The rom mapping was incorrect, with a large range of locations returning random values. Examining the board (since I have no schematics), all of the chip select lines meet up…

  • Make Trax

    Byadmin

    Boot up with garbage, quickly clears screen and then nothing. Used Fluke with Z80 pod – read rom OK, and write ram OK, but timeout reading any Ram location. Check fluke status and ‘wait’ always set. Check pin 24 of Z80– stuck low, trace back through 7H,7C,6C1 to 6B1 pin 2 – always low, although…

  • Namco Time Crisis 2 Gun

    Byadmin

    One of the guns on a Time Crisis 2 was no longer registering shots on the screen. Following checks on wiring, cleaning lens, etc. it appeared that the optical sensor (opto) was dead. This is a small PCB in the gun, 2421961100, pictured above. I couldn’t find any schematics or information about the parts used,…