130 problems - no arc

[ATO]

I've got an old BOC Migmaster that was given to me a few years ago and has been residing in the cellar since. It's the same model as the Snap On/Cebora turbo 130. Have just got it out to brush up as I've got a Series LR bulkhead to repair, was working fine practising on some think angle but after turning it down for some thinner stuff it started to get a bit rough & the wire kept burning back to the nozzle. I turned it up again and now there is no arc at all, the wire just sort of glows and barely marks the steel. The earth connections are all tight, I've cleaned up all the contacts but it's just the same. Can anyone advise what the likely problem is and where I should be looking?

 

[shenion]

Sounds like one of the rectifier diodes went out.

You'll need to disconnect them and check them with a meter.

 

[ATO]

ok thanks. Can you replace the diodes or do would the whole rectifier need replacing? Also what am I testing for?

 

[shenion]

Hard to say without seeing it. Some diodes are pressed in and hard to find.

 

[CKJDJK]

You can buy a new rectifier from technical arc, search on the bay of e £40 +p&p. Was looking for one for mine a while ago.

 

[ATO]

Yes I've spotted them already. Thing is I've stripped down the rectifier and tested the diodes and they all seem to be fine. I had to separate the pairs to test them too so I can't put them back together now!

 

[the snooper]

you don't need to split a rectifier to test it

 

[ATO]

How do you test the individual diodes without taking it apart?

 

[shenion]

Other thing may be the transformer. You could ohm the secondaries.

Only other thing would be a bad connection somewhere.

 

[the snooper]

How do you test the individual diodes without taking it apart?

just connect your meter across each side of the diode

 

[ATO]

just connect your meter across each side of the diode

But if you've got two diodes connected together how can you tell if one or the other is faulty?

 

[the snooper]

power will only pass in one direction through the diode, it wont travel full circle around the rectifier unless they are short circuit, then you welder would buzz very badly when you tried to weld

 

[the snooper]

note the diagram power will only travel in the direction of the arrow it doesn't matter which one you test, another diode will block the path in the circle

 

[ATO]

Ah I see thanks for that.

 

[the snooper]

Ah I see thanks for that.

which has now brassed you off a little more as it sounds like you destroyed it to test it for no reason, can't you put it back together ?

 

[ATO]

Indeed! No it won't go back together as I split the diodes. However I intend to start using the welder a lot more now anyway so it won't do any harm to replace a few old parts lol. That's if I ever get it going again!

 

[mike 109444]

If you connect one lead from your meter to the earth clamp, then set on low Ohms work your way back through the earth side (while your waiting for your replacement diodes to arrive!!) Check the back of the earth socket (if fitted) then the connections on the inductor (if fitted ) usually looks like a large transformer but one lead in and one out. Then keep following back through connections. You will see some resistance but should not be a lot as it's all thick copper but connections are usually bolted = poor connections.

 

[mike 109444]

Another member had similar problem recently and traced it back to the contactor. Was advised to give it a good spray with contact cleaner. If you meter across the contactor first and manually operate to see what resistance is there before giving it a blast (again whilst waiting for your parts....) Don't be tempted to take the power selector switch apart if it's a rotary one. Not unless you have a spare week or two to try and put it back together before chucking and seeing what a new one cost!!!

 

[ATO]

Cheers Mike, I'll give it a go tonight.

 

[ATO]

I've checked for resistance and everything seems fine, however when I test the welder it buzzes and makes the table lights dim that are on the plug circuit, doesn't trip the fuse though and it is pretty sensitive.
Also found burn marks on the secondary transformer. I suppose this means the transformer is the problem and will be too expensive to replace? Good job I haven't ordered the rectifier yet!!