Oerlikon Mini Cito 250 (wire feed)

[swede]

Sorry to post here but I couldn't find a category for my mig welder, so I have a Oerlikon Mini Cito 250 mig welder that I got for free (it's an old one). It was in a garage fire but made it out in time, needed new hose and ground cable. I been welding with it for a while now and it's working just fine except for one thing, the wire feed is to fast.
Even if I turn it down to 0 it still moves to fast for welding on power 1, so I'm wondering if it's just the potentiometer or if it could be something else??

Cheers from Sweden//

 

[a111r]

Welcome.
More likely is the transistor / thyristor on the PCB that controls the wire speed, failing.
They can be tested but need partial removal, so it's easier just to replace it as they're cheap.
Post a photo of the PCB if you need help identifying it.

 

[swede]

Did some measuring, what do you guys think??

 

[eddie49]

Hello and welcome !
The value 0 - 35 Ohms that you measured is too low for a speed pot - at that resistance it would be a wire-wound pot, and this one has a carbon track for sure. There must be other components in parallel which are affecting your reading.
I have see a similar PCB before, the speed control circuit is a Controlled Bridge with two SCRs ( thyristors ) and those two fat diodes, plus a third SCR to brake the motor by shorting across it.

However, the first thing to try would be to turn the preset potentiometer marked "V MIN" ( just behind the speed pot ) to the minimum setting ( anticlockwise ).

 

[swede]

Hello and welcome !
The value 0 - 35 Ohms that you measured is too low for a speed pot - at that resistance it would be a wire-wound pot, and this one has a carbon track for sure. There must be other components in parallel which are affecting your reading.
I have see a similar PCB before, the speed control circuit is a Controlled Bridge with two SCRs ( thyristors ) and those two fat diodes, plus a third SCR to brake the motor by shorting across it.

However, the first thing to try would be to turn the preset potentiometer marked "V MIN" ( just behind the speed pot ) to the minimum setting ( anticlockwise ).

Thanks and I saw that the "V MIN" third leg (close to speed pot) is in direct contact with the speed pot. I was guessing you could adjust the speed on those small pots but wasn't sure and don't want to mess anything up ;-)

 

[eddie49]

This is an earlier thread referencing the same PCB:

Clarke 185e, no wire feed

Hey guys, im Joe, im new to the page. Im in need of some help, i have a Clarke 185e that we had purchased from an auction years ago, i didnt have an outlet to run it (240v). I now own an automotive shop and have an outlet to use it, got everything changed out that was worn,(hoses, wire, ground...

www.mig-welding.co.uk

 

[swede]

I owe a huge thank to eddie49, I did have to turn the potentiometer marked "V MIN" all the way counter clockwise to the stop for the wire feed to not moving when dial at 0. But I rather have a slow feed that I can adjust with the wire feed knob then to fast of a feed.

I will link this forum in my YT video and recommend you guys, your help was super fast and easy to understand. Cheers from Sweden with a working mig welder for my project car :-) :-)