Gas feed problem 185E Solenoid?

[reliant-reviver]

Hi,
have drawn a blank searching the forum on this so I was hoping i could pick your brains.

My old trusty Clarke 185E mig has developed a gas feed problem. The moment the unit is switched on the gas starts feeding regardless of the trigger. I recently replaced the MB15 torch, so am confident that is not at fault.
I have removed the side casing, and to be honest it's all quite unfamiliar to me, I have located the solenoid and visually checked the wiring to it. With a wire removed the gas feed stops, does this suggest the solenoid is kaput? is it a powered close or powered open valve?

Thanks in advance, Phil

 

[Paul.]

Welcome to the forum.
Gas solenoid valves are normally closed, power on to open, so it looks like a problem with the circuit board, most likely the relay contacts stuck together,

 

[eddie49]

Apart from the gas, is anything else permanently "on" ? - i.e. welding current, or wire feed motor? If you remove the torch completely ( assuming it uses a Euro-connector ), does the fault remain the same?

 

[reliant-reviver]

Thanks for the welcome, I've been kicking around long enough, just not posted!

Just checked and the torch also remains live. I think you're right regards the fault being with the relays.

 

[eddie49]

The "small relay" is probably on a printed circuit board, which may be mounted together with the wire speed control on the front panel. There will be an "auxiliary power supply" - small transformer and rectifier, supplying 12 to 24 VDC, the speed control for the wirefeed motor, and this "small" relay. It should ( only ) close when the torch trigger switch is pressed. It will send power to the gas solenoid, the wirefeed motor, and the "big" relay ( "Contactor" ), which switches mains power to the main welding transformer. The relay may have a clear plastic case, or it could be a solid moulded plastic block, about 1" x 1/12". There will be two connections for the relay coil, and two, or more, for the contacts. If you unsolder it from the PCB and the "continuously on" status goes away, then you have found the right component. Next step would be to use a meter to confirm that the contacts are shorted.