Hobart TR-250 HF foot control problem HELP!!

[dooharo]

Hi guys i'm new to the forum and new to tig welding. Recently picked up a Hobart TR_250 HF. I have very little control with the foot petal. Amperage is close to max all the time, control wont back it off. I found a old post http://www.hobartwelders.com/weldtal...-250HF-problem that Hobart expert Keith told how to check out the resistors and voltage to the drive transistor so I did that. None of the resistors are open , get a 1.9-2.0 resistance across them with my meter. What is weird is the voltage to the drive transistor jumps all over the place. Spikes to 30 volts the starts jumping around and falls off to nothing. Same thing at the resistors, max 3.5 volts but jumps around and falls off. I get 0 resistance across the drive transistor,so does that mean it is bad?? I checked the pot in the petal and it smoothly goes from 0 to 25 ohms so I think it is ok. I'm no electronic wizard so i'm hoping you guys can help me out here.

[Northweldor]

Hi guys i'm new to the forum and new to tig welding. Recently picked up a Hobart TR_250 HF. I have very little control with the foot petal. Amperage is close to max all the time, control wont back it off. I found a old post http://www.hobartwelders.com/weldtal...-250HF-problem that Hobart expert Keith told how to check out the resistors and voltage to the drive transistor so I did that. None of the resistors are open , get a 1.9-2.0 resistance across them with my meter. What is weird is the voltage to the drive transistor jumps all over the place. Spikes to 30 volts the starts jumping around and falls off to nothing. Same thing at the resistors, max 3.5 volts but jumps around and falls off. I get 0 resistance across the drive transistor,so does that mean it is bad?? I checked the pot in the petal and it smoothly goes from 0 to 25 ohms so I think it is ok. I'm no electronic wizard so i'm hoping you guys can help me out here.

I assume this is second-hand and out of warranty, but have you phoned Hobart tech support? They are always helpful! ( I'm also assuming that you have been through the trouble-shooting steps in the manual, before calling!).

[dooharo]

Got it fixed , it was one of the 2N3055 transistors. Thanks for the reply. A lot more helpful than the one posted then removed.