Mr. Pinball Tip:

Williams CPU Board Revision Level 7 Test Points

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

A Revision Level 7 board has identical test point values to a Level 6 board, but the test points are in different locations. If your board does not match the location of the test points you have a different board.
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