Another dialarc hf question

[t700Mech]

Greetings everyone, I'm here asking for some help with a dialarc hf, about 1980 manufacture, it's an HK serial number but I forget the rest. The welder tig welds fine in all three ranges, the foot switch stops and starts everything like its supposed to but won't vary the amperage. I traced out the wires to the rheostat and when I actuate the foot switch the resistance goes up and down as it should measured at the plug itself. With the amperage switch in local I started an arc and had my brother spin the dial, the arc got hotter and colder as it should. With the switch in remote the arc would not change either by foot switch or dial. High frequency and post flow are spot on, and the arc won't start until I depress the foot switch so the two pin side works as it should. Any ideas about what I'll find when I pull the cover off? What can I verify inside with a multimeter and no power applied to the machine? I would have already ordered a rheostat but resistance is 16.2 on one side and 15.8 on the other, and it almost exactly inverts

[t700Mech]

Sorry for the triple post, first day with my new forum. Please delete the two others, I don't want to take up on much space.

[Aeronca41]

Welcome! I'm not familiar with your specific foot pedal, but it appears you are not getting a connection between the pedal and the welder. Are you checking the resistance at the "welder end" of the pedal cable? Hard to be specific further without a serial number; I just picked a diagram in th HK ser no series. If the cable & connectors are OK, you either have a bad connection somewhere along that path inside the machine, or your amperage control local/remote switch has gone bad. With the welder unplugged from the power line, put the switch in Remote, and do your resistance checks again between wires 36 & 37 in the welder. If the resistance isn't varying there with the pedal you have a cable or connector problem. If it is, check resistance again between 36 & 38. If it's not varying there with the pedal, the switch is bad.

All of this assumes I picked a serial number diagram that is like yours. Please post the whole ser no.

[t700Mech]

Thanks Aeronca, the serial number is HK 276966. Its a good welder other than that. So hopefully it's just the switch or something that got knocked loose getting it over here. I'll post back after further investigation.

[Aeronca41]

This is not likely to be a big problem. Hope you find it easily.

[t700Mech]

I checked resistance between 36 and 37, it went from .005 with the pedal up to 0 with the pedal down. It varies, but not the same readings as the pedal side of the plug has. I did not read 36 to 38 due to poor lighting. Incidentally right next to the switches there's a bank with CR1,2, and three on it, are they contractors or capacitors and will I get zapped if I touch them?

[Aeronca41]

CR 1,2,3 are contactors. Capacitors would be C1,2,3. Contactors (also called relays) don't hold a charge. However, there could be some caps around with wires connected to them near where you're working, so don't touch other wires.

Sounds like you you have a short in the cable. You should be reading 15-16 ohms at one end or the other of the pedal travel. Disconnect both ends of the cable and check resistance between the wires in the cable. It should be infinite (OL on most digital meters). Check each wire to each other wire. Then verify that each wire reads near zero ohms when you put one probe on each end of the cable.

[t700Mech]

I checked continuity from the rheostat connections to their corresponding blades on the plug, all had continuity and the proper amount of resistance, and it varied the proper amount with pedal deflection. Unless I missed something I'm assuming it good. I removed the local/ remote switch and cleaned all the blades, I checked continuity across the switch and all seemed proper, one side or the other was dead depending on switch position, and the proper wire had continuity when the switch was in remote. I rechecked resistance between 36 and 37, again it went from .005 with the pedal up to .000 with the pedal fully down. Partial depression of the pedal resulted in readings between .005 and .000 as you would expect. I also cleaned all the crap out of the female side of the plug and brightened the metal in there with some emery paper. I checked resistance at the blade the wires slide onto of 36 and 37 and it was the same. What could it be besides the welder end of the plug? I have a very limited knowledge of electricity and appreciate your help.

[Aeronca41]

Will take a look at the diagrams again tomorrow.

[t700Mech]

Well I think I figured it out, I put everything back together and gave it an operational check, I did see a variation in the arc, thinking I had it beat I cranked it back up to the high range and 20% on the dial, and the variation disappeared. I had glossed over the manual for the foot switch but was more interested in the schematic. Turns out that if you want the foot switch to be able to vary the amperage more you turn the dial up to a higher percentage. Reading is fundamental but I did learn a lot tearing all this stuff apart. Aeronca, thank you very much for your assistance,

[Aeronca41]

Glad to help. I apologize for not getting back to you earlier today as promised-just non stop all day long.

I was was going to ask you to check that. Whatever the dial on the machine is set to is the max you can get with full pedal, but you already know that now! Glad it worked out for you.