Quote:
Originally Posted by ScottishColin
Do you mean connect a 4.7k resistor to pin20 of UD9 to a nearby 5V (eg pin 24 of UD9)?
Colin.
Quote:
Originally Posted by Mark1960
If you still see the halfway signals on UE9-2, try connecting a 4.7 k resistor as pullup to nearby 5v. This will hopefully show if that halfway signal is floating or being driven in opposite directions by two different outputs.
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No, I had meant to add the 4.7k from UE9-2 to a nearby 5v.
Looking at the trace in #680, there is no need to try the pull up resistor yet.
It looks like UE9-2 is only just reaching 2v, which might be indicating that the output of UD9 is not as strong as it should be, or that something else is loading that signal more than it should. Instead of UE9-2 use the pin for the same data line on UD9. This is just to make sure the low voltage on UE9-2 is not a poor connection in the socket of UD9.
After you check that, using the same scope settings. Yellow on pin 20 of each of the proms, then green to each of the eight data lines. So what we are looking for is how each data line looks for each of the four proms. Its going to take some time, so if might want to check one prom at a time and let us review while you work on the next one.