Lincoln precision tig 275 foot pedal not reducing amperage

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So I recently had my welder serviced for HF not working correctly on the AC side, installed were new contact points for a spark gap of .015 at the local welder repair shop. Machine now fires up like it should while welding aluminum but there are still some issues. My foot pedal K870 seems to not reduce the amperage after firing up on mild steel tubing 11.ga. When it fires up it feels like it only has one setting and when I try to increase there’s no increase and on the decrease side there is no decrease in amperage. a new foot pedal is $600-700 USD. A new potentiometer for the pedal is $200-250.I’m thinking of returning it to repair shop to try and fix this issue, I’ve already tried checking the POT with a volt meter and it seems to work fine on both terminals to include ground.So my question is could it potentially be the control board which is $1500  and could it be replaced DIY, like a plug in play type deal.while welding 2x2x11ga.steel square tube and where the radius meets the the welding joint I’m getting fisheye type porosity in my tacks and I’m thinking it could be related to amperage. It kind of feels like suck back when pipe welding. any input will be appreciated