Mig welder wire feed problem

[liam99]

Hi Guys,
My welder is over feeding the wire when I let go of the trigger it keeps feeding the wire by 5-10cm. The lance is not that old, I was thinking the relay but is there something thats stops the relay I can test first?
Any help or advice would be appreciated. Thanks

Welder: Multi-weld multimig 181

 

[mike 109444]

There are several ways that manufactures use to "Brake" the feed motor when the trigger is released.
Usually it involves shorting the feed to the motor! This shorting can cause strain on components and failure.
Not sure what is used on that machine but when you refer to the "relay" do you mean a relay on the pcb or do you mean the main contactor ?
Can you see the relay/contactor staying activated for the 5 to 10cm of wire feed when you release the trigger?
Post a pic of the pcb as it may be like a lot of others.

 

[liam99]

There are several ways that manufactures use to "Brake" the feed motor when the trigger is released.
Usually it involves shorting the feed to the motor! This shorting can cause strain on components and failure.
Not sure what is used on that machine but when you refer to the "relay" do you mean a relay on the pcb or do you mean the main contactor ?
Can you see the relay/contactor staying activated for the 5 to 10cm of wire feed when you release the trigger?
Post a pic of the pcb as it may be like a lot of others.

Yeah you can see the relay/contractor staying activated, Its not on the circuit board and it's says Relpol RG25 on it. I'll get some pictures of inside tomorrow night. Thanks

 

[mike 109444]

Did a google image search on that part and this came up.

So if it's the same then if you meter between the A1 and A2 (meter set to AC volts >240) then when trigger is released see if the voltage there drops quickly to zero or if it is staying active for the 5 to 10cm of feed. If the voltage stays on for the 5 to 10cm then the relay is ok. If it drops but feeds on the 5 to 10cm then the relay is sticking internally.

 

[liam99]

Checked the voltage and it stays on, Some pics of the inside.







Thanks

 

[mike 109444]

Is that a chunk blown out of the side of that transistor ?
If that's the braking transistor then that won't help!
Not a lot on the pcb, is there more on the underside ? Or another board.
Just another thought you have not flicked the switch on the machine for SPOT or STITCH function ? (assuming it has those functions)

 

[liam99]

Didn't notice anything wrong with transistor but looking at the picture looks iffy, I will double check tomorrow. I will see if there's more to the board or another one, This is a basic mig on/off switch and amp speed knob.

 

[liam99]

Well that transistor knackered my eyes must be getting worse. Do you think its repairable or what possibly caused it?




Thanks

 

[mike 109444]

Well that device looks fubbered ! You won't fix that! But if you type into ebay "f9540 transistor" you will get hits for a Mosfet device which is what I think it will be. You can get 5 for 0.99p from China ! but probable about 3 to 4 weeks wait. If you look further down the results they are avi from UK suppliers <£5. When you replace it check as you remove the or that there MAY be an insulating strip of a rubber looking material between the metal tab and the ali heat sink OR a plastic looking bush going through the screw hole if either fitted it will need to be fitted on new device. OR there may be nowt !
Reason it may have blown is that the device has a hard life shorting the feed motor when you release the trigger to make the motor grind to a halt. Hopefully a new device may last many years to come. Just hope non of the components underneath are duff cos there surface mount devices and not easy to match due to a lack of part numbers.

 

[liam99]

I've order one from UK seller, Worth a try for a couple of quid. If it doesn't work I'll look for a new mig.
I'll let you know what happens. Thanks

 

[Jim Davey]

Check the big diode on the PCB isn't dead short

 

[liam99]

Late reply been busy at work. Change the transistor and checked the diode ok. So just scrapping it, I've got use of another mig. Thanks for the help and advice.

 

[mike 109444]

Well as the wire feed unit looks better than most small welders it would be worth putting in the "for sale" section of the forum as will fit several other machines I would expect.