Brian E. Brzezicki
Copyright 2013
Version 1.00 11/06/2013

Disclaimer
Use this at your OWN risk, do NOT sue me if it breaks your board... if your doing this your board is probably already broken though ;)

Game Board #1 11/16/2015

Problem:

  • Game is set to free play, however it automatically "starts" as soon as game boots or a game ends, as if someone is always pressing P1 start

Troubleshooting/dianosis steps:

  1. P2 start input is 74LS386 @ 9F pin #12, tested it, it was high (which is normal)
  2. P1 start input is 74LS385 @ 9F pin #14, tested it, it was stuck low (it should only be low if a person is pressing the P1 start
  3. turned game off and checked continuity from 9F pin #14 to ground (looking for a physical short)... no continuity, which means the chip is probably bad
  4. Pulled the chip, socketed and replaced.
  5. Game works properly!
Game Board #2 12/2017

Problem:

  • Game does not work

Troubleshooting/dianosis steps:

  1. Fluke bus test - 10
  2. Video sub board needs new sockets, replaced
  3. Tested video roms out of circuit - ok
  4. Tested code roms out of circuit, 197 tested bad, replaced
  5. Replaced some sockets on code sub board
  6. Sprites are being draw at top of screen where they should NOT be
    See video here
  7. Ended up being 74LS02 @ 3R, replaced
  8. game works!
Game Board #3 2/14/2018

Problem:

  • Screen is blank Troubleshooting/dianosis steps:
    1. Screen is syncing
    2. game is NOT resetting, /RESET is high
    3. Removed code daughterboard, game started resetting, good!
    4. Looks like the game is playing blind, but let's check RAM
    5. Fluke bus test - ok
    6. RAM long 0x8000 - 0x83FF - ok
    7. RAM LONG 0x9000 - 0x93FF BTS 40 - thats 3F - replaced - ok
    8. RAM long 0x9800 - 0x98FF - ok
    9. Screen still black
    10. replaced sockets that hold video daughterboard as the originals were all bent up
    11. No change
    12. Probed SYNC circuits everything probed was OK
    13. Traced backwards from video output, no output
    14. Figured maybe a Blanking circuit was bad
    15. tested /VBLANK - OK
    16. tested /HBLANK - OK
    17. tested /COMPBLANK * - stuck
    18. This is generated by 74LS377 @ 6P
    19. input /CMPBLANK at pin #4 is OK
    20. output /CMPBLANK * at pin #5 is stuck
    21. All outputs of 74LS377 are stuck
    22. /ENBALBE input at pin #1 is stuck high
    23. traced back /ENABLE input to output pin #8 on 74LS10 @ 5D, it was floating
    24. Replaced 5D, now enable line is OK
    25. Screen still blank, but now other output of 74LS377 @ 6P are working
    26. Ouptut pin #5 still broken
    27. Replaced 74LS377 @ 6P, game works!