Bobcat 225 NT CV Problems

[Zrexxer]

I thought maybe I'd throw this out here and see if anyone has any ideas until Miller Tech Support is open tomorrow.

I've got a Bobcat 225NT, production code LA which is a 2000 model. It runs and welds fine on CC processes, no problems there. However, while trying a suitcase feeder out yesterday, I found that the CV setting doesn't work properly.

When set to CV on the selector, the Fine Adjust knob is supposed to serve the function of voltage adjustment between 17-28 volts. However, in both DCEP and DCEN settings, the voltage is stuck around 26 volts and does not vary more than plus or minus a half a volt or so.

Anyone have any ideas on where to start with diagnosing this? It sounds like a component may be open, since the voltage is nearly maxed out. Diode? Bridge? Like I say I'll try and call Miller tomorrow but any suggestions in the meantime are appreciated.

[Zrexxer]

Boy, that was kind of disappointing... I called and talked to a Miller "Bobcat Technician" yesterday and I guess the kindest thing I can say is he was... confused.

Not at all what I'm come to expect from Miller. To top it off, he gave me specs to check the rheostat and I find out later even those are wrong.

Rheostat works and checks out OK. Wiring checks out OK. Connections seem to be clean and tight. I'm been sitting here poring over schematics for two days and getting nowhere.

[ventureline]

Find and check the resistance of R2, should be 5 ohms, check the frequency in HZ idle at the AC auxillaries, (43hz low and 62.5Hz high rpm no load). I'd guess that your high rpm is out to lunch.

[Zrexxer]

OK, I worked it out. I guess it was just the sum of resistances from time and corrosion. I pulled all the push-on terminals loose that I could access easily and cleaned up the lugs with a little steel wool, and it's varying from 25-30V OCV now as it should. They were all a little crusty and dusty from the years.

[FusionKing]

Yea that makes sense...I've had to pull the covers off mine a time or two and fiddle with stuff like that myself.
I love my old Bobber tho