Testing UDN6118/UDN7180 chips for shorts

Steps

• Turn the game off and unplug the high-voltage connector (3J5 or 3J2).
• Set the meter to diode test and put the red lead on ground.
• With the black lead, touch pins 2 to 8 of each UDN chip: expect 0.5 to 0.7.
• Touch pins 11 to 17: expect no reading. A reading here means a shorted chip or a shorted display glass.
• The corner pins 1, 9, 10 and 18 need not be tested.

The display supply runs at about 100 V DC (plus and minus) with large filter capacitors; work with the game off and unplugged, and measure live only with insulated probes.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• UDN6118/UDN7180 pinout and what each failure looks like
• UDN display driver chips
• Check the segment resistors before buying a UDN7180
• Display board chips shown as 4050 are really 4049
• One segment lit on many characters of the top display: unsoldered leg on a driver chip
• High-voltage fuse blows once the display connector is plugged back in
• System 9 versus System 11 display data
• Same segment missing across one 16-digit display

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell