Gorf

ByMichael Coates

Capacitor burnt. (game board), particularly at C37 the capacitor was showing signs of extreme heat. Replaced them all with 22uF 25V axial electrolytics.

No Speech / Some SFX missing. (game board) Output from speech chip SC01 was OK, as was output from IO Custom (X3). checked transistors in output stage and 2N4401 was faulty. (Q2)

Glitches at sides of screen

Screen glitch. (game board) Screens using twinkle circuit (stars etc.) had visible glitches down each side. These did not interfere with game play but looked bad. Tracked down to faulty 74LS161 on game board. (U16 on this one, but also check U15)

Similar Posts

  • 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….

  • Missile Command

    Byadmin

    The board originally failed to get into the game, instead resetting just after drawing the ‘MISSILE COMMAND’ logo. Test mode faired a little better, managing to report RAM OK, MAP OK and ROM OK before resetting. Ram and Rom checked out OK using the Fluke. Measuring various CPU signals revealed that the interrupt seemed very…

  • Atari Tetris

    Byadmin

    In normal mode, just had a blank screen. Enable test mode and you instead get an error message showing that the ROM test had failed (even though the rom itself checks out OK with correct content) This is because the custom Atari SLAPSTIC chip is not functioning correctly. It is used to page banks of…

  • Neo Geo

    Byadmin

    6 Slot – Memory test on power up giving error  Address    Write Read  00008000 5555 55FF Checking with Mame, the memory chips in question were only small, so looking at the board revealed two DIL 5814’s. Chip select signals to these were toggling as expected, so I needed to identify which ram chip was which….

  • 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…

  • Pacman

    Byadmin

    Screen filled with coloured lines, unstable, no sync (see above) – check clock signals from horizontal and vertical scan generators (74161’s at 2R,2S,3R,3S) – no signal feeding into pin 2 of horizontal generators. Follow trace back to 7474 at 3N, signal going in, nothing coming out – replace chip and screen display back to normal….