Upgrade logic rectifier diodes D7 and D8

Steps

• On System 3-6 power supplies, remove the 3 A MR500 diodes at D7 and D8.
• Fit 6 A diodes: 6A4 (400 V), 6A2 (200 V) or 6A50 (50 V), with the band the same way as the original.
• Check connector J1, which feeds these diodes, and replace it if it is heat damaged.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A

Related tips

• Replace the +5/+12 V logic filter capacitor
• Spare diodes, capacitors and resistors for System 3-7
• Judging the logic filter cap by AC ripple
• +5 V logic low or noisy
• Display supply low (under 90 V) after the resistors are changed
• Cross the legs when MJE15030/15031 replace SDS201/SDS202
• High-voltage supply rebuild parts, System 3 to 11C
• Fitting the high-voltage kit

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)