I have an Atari Liberator board with a pulsing /RESET line. The /RESET signal comes from pin 12 of the LS197 @ J11, fed by the watchdog & power-on reset circuits and some other inputs. I have verified that both the watchdog output (pin 3 of L4) and the power-on reset output (pin 1 of K12) go high as expected. 3 of the 4 inputs are tied to ground and 1 to +5v.
I could tell the LS197 had been previously been pulled and maybe replaced. I pulled it to test just in case but it tested OK. I even piggybacked it onto a working board with the /RESET pin bent out and it was held high as would be expected, so I'm sticking with the chip being OK.
This lead me to believe the 128V signal on pin 8 is the cause. However looking at it with a scope, it didn't look much different than that on my working board. There was some noise (a slight 'fluttering' on the trace of the waveform) but the peak and frequency was the same. Since the Liberator schematics had signatures, I used my analyzer and found all sigs for the LS163 @ H8 (which feeds J8) and the LS163 @ J8 (which creates the 128V signal) matched. Side note... I though the signatures published in Atari schematics were only for a CatBox and would not match standalone analyzers. However my HP5006A displayed the listed sigs exactly.
So if the 128V signal is good, the watchdog and power-on reset are good and the chip itself is OK, what else could it be? I thought it could possibly be another chip feeding back on the line, but when I bend out pin 12 and power on, the /RESET line is dead (neither hi nor low), so that's the source of the signal.