fuse blowing

[pause22]

Hi i am new to this so be gentle with me,
I have a snap-on mig everything works fine wire feed button ,trigger on torch works but when you try to weld (strike an ark to earth) the fuse in the 13 amp plug blows does anyone have any ideas?
thanks Sean

 

[the snooper]

does it make a loud sort of violent buzzing noise ? if so could be the rectifier if not welding transformer gone

 

[normspanners]

Try disconnecting the output from the tranformer before the rectifier leave it 'free', and then see if it blows, thar jim me lad!

 

[pause22]

thanks yes it does make a loudish buzzing noise

 

[rtbcomp]

Do you get these symptoms on all power settings?

 

[pause22]

hi on setting 1 you need to strike an ark to get the fuse to blow ,on max power the fuse blows soon as you press the trigger.

 

[rtbcomp]

Looks like a machine fault then, just wanted to make sure you weren't overloading the mains.

I would suspect the rectifier in the first instance.

 

[pause22]

the rectifier has 2 components that look like diode packs,they look the same but test different with a meter.does anyone know if they should have the same characteristics?
part no MDD90-04 A8927 ART NR 64.0065.04
cheers sean

 

[rtbcomp]

How different do they test?

Any that show a low resistance in both directions are duff.

If one or more are duff I would replace the whole lot as a matter of course. Maybe even get some with a higher rating?

 

[pause22]

Each module has 3 terminals,looking at the diagram on the module i measure across each diode and get a reading of 12.7k but on one module have no reading across one diode.
i guess that's the duff one.problem is i cant find this part anywhere and don't really know what to look for as a replacement

 

[pause22]

hi disconnected the rectifier and fuse does not blow have tested both diode blocks one seems faulty but cant find where to get a replacement

 

[pause22]

must learn to use my test meter properly the diode with a different reading is actually a dead short across the terminals

 

[rtbcomp]

That's the one then!

I suspect I know what they look like, but can put a photo up? I'm sure someone will recognise them and be able to suggest an alternative.

 

[pause22]

Thanks everyone for all your help have ordered part,fingers crossed.
cheers sean

 

[normspanners]

Well done that man, where bouts are you I'm just over the border .