When I disconnect the fet driver wires from the control board, the fet driver pulse works fine. It no longer locks in the on state. Also when the ground lead for the fet driver output is attached near the grounds where the pots are attached, positions 6 & 7, it causes that pot to wander all over the place. So I soldered it to the ground hole near position 1 on P3. That corrected that wandering issue. Still the output gets stuck on. At least one press of the foot pedal corrects it. It almost looks like a ground loop.

Here is what the fet driver input signal looks like on the control board when the spot welder stays on. Trace #2 shows that it’s just stuck full on at 5vdc. This holds the fets in the on state and that’s why the probes are energized. The power supply is straining to keep up with the constant load instead of the milliseconds long pulses that it normally sees.

This is what the fet driver input signal looks like when operation is normal.