Foot Pedal Not Working

[GESCHWARZ]

I have an old P&H TIG welder that has been very reliable, but lately I've lost the ability to control the strength of the arc with the foot pedal. I've checked the wires and connections inside the pedal at the reostat and they are all good. Where else should I look to solve this problem?

[usmcpop]

Check the resistance value of the rheostat inside at the terminals and again at the end of the cable. Make sure that it is equal and up to spec. Then work your way upstream. Check to make sure the rheostat isn't cracked or damaged.

[GESCHWARZ]

Check the resistance value of the rheostat inside at the terminals and again at the end of the cable. Make sure that it is equal and up to spec. Then work your way upstream. Check to make sure the rheostat isn't cracked or damaged.

I don't have the spec. What sort of resistance should I expect to see on the rheostat?

[urch55]

I don't have the spec. What sort of resistance should I expect to see on the rheostat?

Even if you don't have the exact specs. you can still see if the pedal is working or a broken wire going to and from it.
Would seem like with the pedal up (not pressed) there should be no reading or very little, then as you press the pedal down that reading should increase (just like touching the two leads of the meter together).

[usmcpop]

I saw mention of one where the Arctrol varied from 0 to 11 Ohms. But as long as it does vary from step to step and you get the same at the other end, you should be good to go. Take care of that pedal, they are rare.

[GESCHWARZ]

Okay, thanks. My next question might be, if the foot pedal and cabling is all good, what inside the machine might be bad?

[usmcpop]

Can you still adjust current without the pedal?

Is there a schematic inside on one of the panels?

[GESCHWARZ]

I measured the resistance of the Arctrol Cutler-Hammer rheostat. It reads about 2 or 3 ohms just about anywhere I put the two probes. It is as if it's shorted out. Or it could be that my ohm meter doesn't read well down that low of resistance. I'll take it to work tomorrow and use the ohm meter there.

[GESCHWARZ]

I was able to measure the resistance of my rheostat with a better multimeter and I have found that the rheostat appears to be good. It measures 6.5 ohms at full range and graduates in a linear manner to 0 ohms. So my problem may be with a bad connection. All the connections I've checked so far appear to be tight, so perhaps they need to be taken appart and cleaned. I'll first check for continuity.

[Northweldor]

I was able to measure the resistance of my rheostat with a better multimeter and I have found that the rheostat appears to be good. It measures 6.5 ohms at full range and graduates in a linear manner to 0 ohms. So my problem may be with a bad connection. All the connections I've checked so far appear to be tight, so perhaps they need to be taken appart and cleaned. I'll first check for continuity.

Especially the rheostat-to coil finger.

[canoecruiser]

When the pedal is plugged in and the welder is on, is there any voltage across the rheostat? Perhaps the problem is internal.

Edit: DOH! You already thought of that....

[GESCHWARZ]

PROBLEM SOLVED! All I had to do was take apart the three connections, one at the wiper and the two at the rheostat and clean all the contacting surfaces with a wire brush the same way you do with your car battery terminals. I then put it together and fired that mutha up and ran a bead, and Presto(!) I have control of my arc strength!

While I had it all apart I checked for the resistance of all the wires in the cable and I checked for shorts between the wires. All looked good.

Lesson learned: Car battery connections aren't the only connections that can get oxidized and dirty and need a little maintenance. The range of resistance between minimum to full is so small (zero to 6.5 ohms) that any amount of resistance in the connections is going to send a weak signal to the welder.

That old P&H was ancient when I bought it for a thousand bucks about 35 years ago. It runs as good today as the day it was made, I'm sure.

Thanks for your help guys.