Load-testing BR2 in the game with a 6 A diode

Steps

• You need a meter, two clip leads and a 6 A rectifier diode (6A50, 6A2, 6A4 or similar).
• Game off. Clip a lead from the "+" terminal of BR2 (the top bridge; "+" is its top-left lead) to the meter's red probe. Black probe on the backbox ground strap; meter on DC volts, 20 V range.
• Turn on: expect 12-13 V. Under 12 V means the bridge or its connection is bad.
• Game off. Clip the second lead to the banded end of the diode and its other end to the red-probe side of the first lead.
• Game on. Touch the diode's non-banded end to the exposed metal of J101 pin 1 or 2 (top pins) without unplugging it. A change in the reading means a bad positive diode inside BR2.
• Game off. Reverse the diode in the clip, move the clip lead to TP5 (ground), turn on and touch the banded end to J101 pin 1 or 2. A change again means BR2 is bad.
• If nothing changes and the reading stays above 12 V, suspect C5 (15,000 mfd 25 V), C4 (100 mfd 25 V) or cracked solder at the bridge or capacitor.

Line voltage is present in the cabinet and backbox with the game on; keep hands clear of the transformer and power wiring.

Systems

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

Related tips

• Replacing BR1 and BR2 on their shared heat sink
• Replacement bridge rectifier and diode ratings
• Won't start after a power surge, 5 V reads very low: failed C4 on the power driver board
• Row 1 short error and F114 blows at once: fault in the 18 V lamp supply
• Every opto dead and the opto board LED off: failed bridge BR5 for the unregulated 12 V
• 12 V and 50 V supplies read far too high: transformer line-voltage jumpers set wrong
• 'Check F114 and F115' with switch 24 open: missing 12 V, bad bridge BR5
• Voltages made by the WPC power driver board

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