Take a close look at the signal amplitudes (best to use a scope); if the resistor values are causing the logic gates to be overloaded [either due to wrong IC, wrong logic family, wrong resistor value, solder short/open] , you will see incorrect levels. Generally, logic-0 will be 200mV or less (despite the specs being Vol(max)=0.4), and logic-1 around 4V (despite spec being Voh(min)=2.4). Remember - clock signals are critical; they must have clean edges and should swing rail-to-rail. Anything other than this should be suspect.
In my previous life as a technician, one of the first things we did when debugging a large PCB was to hunt-around ICs for bad signal amplitudes. It took less than a minute to probe a large section, and that method found many problems (wrong IC, backwards IC, bent pin, solder-bridge, bad PCB trace, bad socket). In *rare* cases, the actual IC was bad, which seems counter-intuitive until you realize these devices are thoroughly tested by the manufacturer. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/7cacddaa-8d1c-4e45-810e-bfc7e530eef7%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
