Rebuilding the dot matrix high voltage section

Steps

• Confirm the fuses are good and the display works in another game.
• Raise the playfield and check the transformer connectors in the cabinet bottom for loose or oxidised terminals.
• Replace Q6 (MJE15031), Q7 (MJE15030), Q3 (Q1 on WPC-95, MJE15030), Q4 and Q5 (MPSD52 or 2N5401), Q2 and Q10 (Q2 and Q3 on WPC-95, MPSD02 or 2N5551).
• Replace D4 and D5 (D1 and D18 on WPC-95, 1N4758 56 V), D6 (D3 on WPC-95, 1N4742 12 V) and D3 (D2 on WPC-95, 1N4759 62 V). On WPC-S and earlier also replace Q1 (2N3904).
• Check all resistors are within 10%; replace any out of spec or burnt, and replace cracked 5 W resistors even if they measure good.
• Mount the resistors slightly above the board for airflow.
• Replace every part in the section at once: one bad part left in can take out the new ones.

This circuit makes over 100 V DC. Work only with the game unplugged and check the filter caps are discharged.

Systems

• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Dot matrix display supply voltages
• Dot matrix display power connector pinout and voltages
• What the WPC dot matrix controller does
• Dot matrix display blank or faulty
• One or two display columns stuck on
• Resets caused by a failing dot matrix display
• Dot matrix display faults
• Blank display, garbage or diagonal lines: reseat ribbon cables

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