Flickering dots after repairing an older REV 6 DMD controller

The later -12 controller adds a 74HCT138 at U12 to cure a timing race that newer, faster RAM and logic chips expose. If a REV 6 (-00) board shows wandering or flickering dots after parts were replaced with modern chips, this race is the likely cause. Fitting the chip alone does not upgrade a -00 board; swapping in a -12 board does.

Systems

• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)

Related tips

• What the WPC dot matrix controller does
• Dot matrix display supply voltages
• Rebuilding the dot matrix high voltage section
• Dot matrix display blank or faulty
• Dot matrix display power connector pinout and voltages
• One or two display columns stuck on
• Resets caused by a failing dot matrix display
• +62 V wrong: burnt trace under R9

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part One, Clay Harrell (pinrepair.com)