Ignore the SW1 memory test unless the board has booted

The CPU's SW1 diagnostic is only a memory test of IC19 (5101) and the static RAMs IC13/IC16, run from code in the flipper ROMs. If the board has not booted, its results mean nothing and lead to replacing good parts. LEDs stuck on at power-up (or "0" stuck on System 7) simply mean the CPU is not running.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• System 3-6 SW1 test results
• Memory protect chips to check after the 5101
• Leon's memory test results (versions from 11/01/03)
• System 7 SW1 diagnostic codes
• Board boots and passes SW1, but no displays or CPU lamps
• Run the System 3-6 built-in CPU test (SW1)
• System 7 board with older firmware shows "u" on the SW1 test
• Leon's older memory test read with a tester LED

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