The spot welder is finally working now! It was the fet driver signal from the processor that was not going back to ground after it sent the dual pulses. I added a couple of different values of resistor and placed them from the fet driver signal on the processor’s pin 27 (terminal block position 17) to ground. I ended up soldering the 2.2k resistor onto the right side of R27 and the left side of R22 for a permanent installation. 2.2k worked the best and draws only an additional 2ma. The I/O pins are rated at 25ma on the processor data sheet.

What also helped a lot was not connecting the ground lead for the fet driver to any of the grounds on the terminal block. When it was attached to any of the terminal block grounds, the spot welder kept sticking on. So I soldered it to the ground pad of C9, which is one of several parts not installed per the manual. It worked far better after that. This fet driver ground lead location was always contributing to the sticking on issue.

I also added a 1k resistor in series with the fet driver input signal so that when the fet driver fails shorted, it won’t take out the processor as well. When the first fet driver failed it was forcing 3.4v into the fet driver input circuit. Which forces pin 27 of the processor to 3.4v when it’s trying to stay at ground.

Now it’s time to get accustomed to using the settings to make good welds! All I have right now is .010″ thick nickel for testing. My aim is to spot weld braided cable for the combat robotics folks.