After the game was switched off and on repeatedly, the dot-matrix display stayed blank and fuse F602 on the audio/video board blew every time it was replaced. The rest of the game played normally.

DMD blank and F602 blows after rapid power cycling: bad D11, then a reversed ribbon

Cause: Diode D11 in the display high-voltage supply had failed. After it was replaced the fuse held, but the display stayed blank because the display video ribbon cable had been plugged in the wrong way round during the repair.

Checks

• Test D11 and the other high-voltage supply parts if F602 keeps blowing.
• Measure the display supply voltages at the DMD power plug; readings of about -117/-105 V, 65 V, 12 V and 5 V are within tolerance.
• Check the display ribbon cable is fitted the right way round at both ends.

Fix

• Replace D11 and fit the correct F602 fuse.
• Refit the display ribbon cable correctly.

The display supply carries over 100 V DC even with the game just switched off; let it discharge and work with the power off.

Systems

• WPC-95

Games

• Junk Yard

Related tips

• Spare plug marked DOT POWER (J604) after a move: only for the original display
• Blank display, garbage or diagonal lines: reseat ribbon cables
• Dot matrix display blank or faulty
• Dot matrix display power connector pinout and voltages
• Which dot matrix displays fit WPC games
• Resets caused by a failing dot matrix display
• DMD line out from a broken pin at the glass: bridge it with conductive glue
• Display shows garbage or nothing though the glass is fine

Source: Pinball Repair help group!! (Facebook group)