Mr. Pinball Tip:

Williams CPU Board Revision Level 6 Test Points

TP1 = +12 VDC unreg. (upper left)
TP2 = NMI, +5 VDC (upper left, up and right of TP1) It should read 0 VDC when diagnostic switch SW1 is pressed.
TP3 = Memory Protect (upper center) +5 VDC when interlock closed, 0 VDC when interlock open.
TP4 = Blanking (left middle) +5 VDC normal operation, 0 VDC blanking (when first turned on for about 1 second).
TP5 = IRQ (lower left of center)
TP6 = BUS 02 (lower and left of TP5)
TP7 = CMOS RAM B+ (lower center) +4.3 VDC when power on, +3.9 VDC when power is off. If this is low, your batteries are low.
TP8 = RESET (lower left corner of batteries) 0 VDC for first second that power is on, +5 VDC after that.
TP9 = +5 VDC (lower right)
TP10 = Ground (lower right)

A Revision Level 6 board has a part number on the lower right corner ending in a 6 or 6A, or something similar. If your board does not match the location of the test points, or if the part number differs you may have a different board and some of your test points may differ.
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