So I'm debugging a dead PDP-11/23 board (M8186). The first thing I check is the clock; specifically the output of the first stage buffer-inverter (pin 16 of E4, a 74S240, upper right corner of page 2 of the prints), which is distributed to a number of places. Nada. Totally flat-lined. So I checked the input (pin 4), and it's sitting at about 2V. Also flat-lined. This does not seem good... :-) So here's my question: what's the likely fault here? The only thing upstream of that gate is the 13MHz crystal itself. So the fault has to be either the crystal or the S240 (which seems to be some sort of octal 3-state inverting buffer). Any guesses as to which? As usual, thanks in advance for any help! Noel