On 2015-Feb-05, at 2:16 PM, Noel Chiappa wrote: Well, try removing W1 to isolate the output of the xtal oscillator E15 from inverter input pin E4.4. Then scope the output from the xtal oscillator to see if it's OK. If you're not familiar with them, E15 is an integrated xtal oscillator, not just a crystal - the crystal and oscillator logic are both in that can, the output should be a nice square-wave/pulse at logic levels. Those cans generally have the four corner pins/wires present for mounting stability, +5 and GND are in the usual places, pin 8 the output. (Also confirm +5/GND are good at the appropriate pins.) Could also (with W1 removed) pull E4.4 hi/lo while watching the inverter output E4.16 to see if it responds correctly with the inversion.