Gorf repair log – Player 2 button stuck closed

Status: FIXED

Repair cost: 6 cents

KLOV Post: http://forums.arcade-museum.com/showthread.php?t=106860

Symptom:  2 coins always starts 2-player game.  Checked diagnostic screen and it showed P2 button always closed.

Diagnosis: Continuity between common ground (orange/red) and P2 button (red/yellow) lines all the way back to the board.  Problem on mainboard.


  • 10/15/09 – P2 button: Pin 19 on J1 connector.   Runs thru R16, R32 which tested good.  Traced P2 line back to U3 (a MC14539B multiplexer IC) pin 10, which was stuck high.
  • 10/19/09 – With the help of a friend, realizing pin 10 on U3 is an input, something upstream must be causing the high signal.  Tested U3 for shorts (conductivity tests between inputs/Vcc), everything tested fine.  A series of pullup resistors and a cap is upstream of that pin….  Pulled resistors, which tested good.  Pulled C16 (104Z ceramic axial cap) which tested bad.  Waiting for parts.
  • 10/24/09 – Replaced C16, P2 no longer closed.

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