Power Ultra 205 amperage throttling fail

I have an older model but I have kept it in great condition and have only used it on few occasions. What I have noticed is that when Tig welding with the pedal the amperage will not modulate up or down. If you turn the potentiometer inside of the pedal, the the amperage will display from low to high as you turn the pot. As soon as limit switch is activated amperage no longer modulates, This is not a pedal problem, can anyone help me out, I am a electronic tech, I could probably figure this problem out if I had the schematics?

The pot is typically wired in as a voltage divider, so the first thing I would do in any circuit troubleshooting is check voltages.

I am waiting for tech support as of this moment.
Amperage can only be adjusted when start switch is not pressed, I can set it on the local control, but once you push the button it stops working,potentiometers work fine and control the amperage led display, there is just no control while welding. Has to be something with the control board inside the unit.

Made some progress troubleshooting. I don't recommend anyone who is not trained with the hazards of electrical shock to take the cover off of their welding unit. Also, if your unit is under warrantee, leave this job to the service techs. If you yourself are a tech(unplug unit and be careful of charged capacitors) , I recommend unplugging connectors no more than one at a time and plugging back in to reseat the connectors. My welder seems to be functioning again, no time right now to weld up a piece, but I will keep posting.