[ScottishColin]

UB2-11 goes high on the scope and with a meter I can confirm the voltage is 5.16V.

Colin.

Originally Posted by SiriusHardware

Ref: The results in #1166. Nicely done.

I take it the pin 9 signal in all of those was the yellow (lower) trace?

What your captures tell us is that there are times when all four of those chip inputs are low (0V) at the same time. One cycle on pin 9, which comes from buffered A15, represents one full sweep through all of the address range with the falling edge marking the beginning of the sweep at address 0000.

Two of the inputs are low full-time, probably held that way by links, and one other, pin 13, is low at the same time as all the others for at least some of the time.

When all of the input pins of that UB2 gate are low at the same time, we should see a high (4-5V) out of UB2 pin 3, but we do not. This would suggest that the UB2 gate is faulty. However, please check that you definitely have a 'high' (4-5V) on the 'G' enable pin, pin 11, of UB2.