Snap-on Promig 170 gas won't stop

[GT4Jools]

Hi,

My Snap-on Promig 170 has developed a problem where the gas won't stop coming out. The wire only feeds when the trigger is pulled but the gas solenoid clicks as soon as you plug it in. I'm pretty sure it's a circuit board issue. My question is, has anyone else had/rectified this issue or does anyone have a circuit diagram for it so I can have a go at fixing it myself.

Cheers

 

[Barking Mat]

Welcome to the forum, sounds like a sticky gas relay solenoid.

Have you stuck a multimeter on it to check ?

Could be the board though.

 

[zzr1200]

Pull the wire off of the gas solenoid if it's still leaking gas the valve unit is screwed, if it stops the board is fried (probably) unless there's a relay involved...

 

[tom2207]

if its not been used in a while ,,, tap the solenoid case with something sticky ,,,
like a stick. or a screwdriver handle ,,, maybe just gummed up a bit . then order a new one ,,, but if it gets you going for a while .
Welcome to the forum.

 

[GT4Jools]

Hi,

Thanks everybody for your replies. I didn't expect responses so quick so wasn't checking the forum.

It's not the solenoid, if I unplug it, the gas stops. The click that happens when I plug the welder in is coming from the solenoid so something is giving that feed even though the trigger isn't pulled.

I had been using the welder when the problem started and it's used regularly so nothing to do with lack of use. Whatever is at fault had played up momentarily about 30 minutes previous but then seemed to cure itself. I get the impression it's a relay that's welded itself together. I assume there's a relay that feeds the gas solenoid but I just don't know which component that is. As I say, a circuit diagram would be really handy, or if anyone knows what the relay looks like, I could just buy one and fit it...

 

[GT4Jools]

I checked the lance with a multimeter by the way and it's working fine - as you'd expect because the wire feds as normal.

 

[eddie49]

I believe that the Snap-on Promig 170 is a re-badged Italian Cebora Stag 186, there are several earlier threads on this Forum that confirm this. The Cebora product number is "Art.532-21"; you may find this number on the Snap-On data plate.
Technical information, including a general circuit diagram of the welder, is available on the Cebora website:

https://welding.cebora.it/en/assistance/items-out-of-production/art-532-21-stag-186

The diagram is "sch_532-21.pdf".
There is no detailed diagram for the PCB. A picture of the board can be seen on this Tec-Arc eBay listing, offering a component-level repair service:

Mig Welder Cebora Stag 186 (needs repairs) | eBay

Find many great new & used options and get the best deals for Mig Welder Cebora Stag 186 (needs repairs) at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

The TIC126D power semiconductor is a thyristor ( SCR ), which probably is used to provide speed control for the wirefeed motor. That circuit will be supplied by the welder output voltage, and enabled by the torch trigger switch.

The small 27v 1.5VA encapsulated transformer mounted on the PCB drives the Finder relay. From the diagram, I think this relay enables power to the gas valve ( item 15 ) in parallel with the primary of the main welding transformer ( fed via the voltage range switch - item 24 ). If correct, this implies that if, for example, the relay contacts have welded shut, then in addition to continuous gas flow, there should also be DC voltage at the tip of the MIG torch. I would suggest checking for constant continuity across the relay contacts, at the push-on tags "A" and "B" of the PCB at location RL1.

 

[GT4Jools]

Thanks Eddie49! You're right on the money!. There was constant power at the torch and, as you said, continuity across the push-on terminals RL1. I've just removed the PCB so all I need to do now is source a new relay and I'm back in business!

Cheers!