Testing buffers U11 and U13 (74LS244)

Steps

• A bad U11 or U13 stops the board booting at all.
• Game off, meter on diode test. Red probe on pin 10 (ground).
• Touch the black probe to pins 1-9 and 11-18 in turn: expect 0.4 to 0.6 V.
• A zero reading means a shorted chip: replace it.

Systems

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

Related tips

• System 11 switch matrix: connectors and chips
• Switch matrix dead after an under-playfield adjustment with power on
• Fixing a dead switch column on the CPU board
• Switch column (drive) circuit on the CPU board
• Whole switch column dead after working under the playfield
• One switch column dead: parts to check in order
• Dead CPU: the order to replace chips
• Checking the CPU data lines and buffer U16

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)