Sealey mightmig 100 wont weld or feed wire

  1. Nivlac939 New Member

    Hello everyone ! New to forums, been reading about for abit now! So I have a sealey mightymig 100 gassless welder. I was doing some welding on the van and ended up the torch was abit messy by end so stripped it down to clean and I forgot to turn the power off when stripping the handle, idiot move I know. So the trigger wires ended up hitting a block of metal behind it which is used to Earth the torch gun. So after it touched, got a pop. Replaced fuse although was still powering up. Checked fuse on pcb. Replaced anyway. No joy, no welding current at torch and motor won’t feed wire on clicking it. I had a spare motor there and new pcb. Fitted both and still no joy. Pcb has the speed control module on it too. Tested motor and both work. Removed Earth from torch and ran new Earth to test. Issue still same. Won’t weld and motor won’t feed wire. Can’t see any burnt wires or anything that looks wrong?!?

    Only other thing I can think is Rectifier is blown?!

    any help would be great before i go buy a new one haha!
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  2. a111r Member

    I'd check the trigger switch is working properly. What you describe has happened wouldn't usually destroy anything.

    This used to be a decent enough model, until maybe 5 years ago when Sealey decided to 'make them' in China.

    The data info. on the front shows that they don't have a rectifier. They are AC MIG welders, as in without DC welding voltage!
    The minimum current is also 55 Amps... essentially making them pointless, as an arc welder does this.

    So don't buy another one.
    Hutcho and eddie49 like this.
  3. eddie49 Member

    Hello, and welcome to the Forum!
    That is certainly possible, but I would expect it would take more than just a little "pop" to blow a 100A rectifier.

    Here are some troubleshooting hints: ( * * Only do this if you are confident working on live AC mains powered equipment ! )
    The PCB has a small transformer. The primary side should have 230v AC mains on it, and the secondary about 12v or 20v AC. When the torch trigger is pressed, that operates a small relay ( only ) that is on the PCB in a plastic case. You should be able to see and hear the relay click. The relay closes and feeds AC mains to the primary of the main transformer. You could simulate this by removing the plastic case and wedging the relay armature in the "on" position. The secondary sends from 15v to 30v AC ( depending on the setting of the power range switches ) to the rectifier. The DC output from the rectifier powers the main welding current, and also drives the wirefeed motor via the speed control part of the PCB.
    Following the above flow should assist you in locating the fault.
    a111r likes this.
  4. a111r Member

    IIRC, the triggers on these use a micro switch.
    I'd start by looking at whether it's working or if the two wires have got damaged, when you replaced the torch casing.