Halp meh, Oh halp meh!!

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bruggz351
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Halp meh, Oh halp meh!!

Post by bruggz351 »

Ok, now that I've lured you into my trap 8o|
can some one please tell me if this pcb is ok or shafted???
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It's from my Mig welder, which keeps throwing the overheat, sometimes before I even weld :@ so I know it's definitely NOT hot.

Does any body know where the thermistor is on a welder? Can it be changed out?
I've had a look around and can't find anything obvious to me, like hot spots or burnt wires. I've blown it all out with compressed air and still no joy.

I don't mind spending a little on this welder, as it's a cigweld brumby and I only paid $100 for it.

Any help will be greatly appreciated.

:thumpsup: :thumpsup:
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Jordan1249
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Re: Halp meh, Oh halp meh!!

Post by Jordan1249 »

where 84 he'd know
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LukeAussie
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Re: Halp meh, Oh halp meh!!

Post by LukeAussie »

Hmmm, it's a little hard to say from looking at the PCB there... can you take a photo of the underside?

Is the fault something that you can reset, and if so, how do you do it? This can help to narrow down what may be happening (and electronics is my game, so I'm happy to help with a bit of troubleshooting :) )
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bruggz351
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Re: Halp meh, Oh halp meh!!

Post by bruggz351 »

No, it can't be reset. It's just a little red light on the front with a thermometer symbol next to it. You stop welding, ( well, ya gotta. It stopped ya :P ) let it sit for a few minutes humming away until the light goes out then try again. Some times I can get a centimetre bead, sometimes only strike an arc and it'll trip again. :(

It will do this from cold. No welding done at all. Turn it on, Earth it, strike an arc and .... trip!!! :banh:
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ddt
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Re: Halp meh, Oh halp meh!!

Post by ddt »

dunno that much about welders but a thermistor would need to be where it's hot (not on the PCB) and it decreases resistance as it gets hot. I would say if it is no go at room temp then it has probably failed (closed circuit -not open circuit). Try and find which two wires go off to the thermistor, (maybe the black and grey at top of pic?), disconnect then try to turn it on. If it works then its a bad thermistor.
Of course if it works without a thermistor connected, you will have no overtemp cut off.
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mrd
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Re: Halp meh, Oh halp meh!!

Post by mrd »

Unless something was glued to that capacitor, I'd say that the bubbly liquid leaking out the top of it isn't a great sign (though I'm no expert).
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84GKSIG
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Re: Halp meh, Oh halp meh!!

Post by 84GKSIG »

sent you a PM :thumpsup:
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LukeAussie
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Re: Halp meh, Oh halp meh!!

Post by LukeAussie »

HOw are you going with this one... I'd be inclined to think it was an issue with the temperature sensing device (thermocouple or thermistor), which will be located elsewhere. I'd be looking for leads from the PCB to the device, and perhaps look at changing the part (to test, you can always remove it from the system and check whether the unit works - it may not, depending on what protections are built into any control circuit).

I wouldn't be overly worried about the capacitor, as normally the electrolytic caps blow to pieces when they die (the plastic would be ripped off and there'd be only part of the casing there. But check the PCB below the cap anyway, in case it's blackened or anything like that...

Good luck!
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bruggz351
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Re: Halp meh, Oh halp meh!!

Post by bruggz351 »

Well, it's currently in bits 8o| and I'm about to send poor 84 a shite load of pics :$ . Thanks man... :thumpsup:

:D
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bruggz351
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Re: Halp meh, Oh halp meh!!

Post by bruggz351 »

Righto then... first job, replace those capacitors...

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picking up one of these from Jaycar tomorrow for $25.. cheapaz (H) :thumpsup:

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.. already takin me back to me highschool electronics days... :D hope I remember enough to get me through... :lol:

Strange, but I think I'm enjoying this little project more than the car. :| :hit: (A) :lol:
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LukeAussie
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Re: Halp meh, Oh halp meh!!

Post by LukeAussie »

Ha ha, fun times! If you get a chance, I recommend getting de-soldering braid (it's basically like a copper shoelace), as it's slightly easier and more effective than a desoldering tool, but whatever you prefer...

Good luck with it!
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Re: Halp meh, Oh halp meh!!

Post by 84GKSIG »

if you do choose to use de-soldering braid instead of a solder sucker, get the braid with flux, it will make your life less difficult and dosent cost that much more :thumpsup: shouldnt be too hard with a de-soldering tool though, braid i find is excellent for cleaning pads before using new/different solder if you choose to be that fussy.


how did you go with the caps :D
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bruggz351
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Re: Halp meh, Oh halp meh!!

Post by bruggz351 »

[quote="bruggz351"]Righto then... first job, replace those capacitors...

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picking up one of these from Jaycar tomorrow for $25.. cheapaz (H) :thumpsup:

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Got the soldering iron kit. Hehe. Chingrish...
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Righto, got the 2 smaller guys, 63V 100uF. They heaps of them. The bigger one, it's a 50V 1000uF. Poor young bloke behind the counter, geeze he did a good job. Took us 15 mins of searching, on the computer, in catalogues, on the internet. LOL... In the end, he started going through the drawers. Holy fark, have you seen how many little drawers they got there? :| Any hoo, he says " I have 16V 1000uF or 63V 1000uF, but no 50V's " Where they're supposed to be is a hole in the wall... :banh:

Oh well. I'll replace the 2 smaller ones as these are the ones that look the dodgiest. I may try and get 1 online....

To be continued... :thumpsup:
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84GKSIG
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Re: Halp meh, Oh halp meh!!

Post by 84GKSIG »

no real problem with going over spec on the voltage ( just dont go lower voltage than whats already in there ) if that little of a difference and that low of a voltage, ESR wont come into play much, as long as its temperature rating and capacitance is the same value :thumpsup: and of course physically fits in that space on the board.
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bruggz351
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Re: Halp meh, Oh halp meh!!

Post by bruggz351 »

:thumpsup:
Thanks 84. I'll grab the 63V 1000uF then.
I was surprised at the cost. $0.70ea for the little fellas. The big one is around the dollar mark. :wut:

Cheers
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bruggz351
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Re: Halp meh, Oh halp meh!!

Post by bruggz351 »

Well, I did this...
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... shiny black ones.. 8o|
which totally shut it down.. :o but, that was good, as now the circuit was working properly. and made it possible to track the culprit down. A bung thermistor. Bridged it's contacts and the welder came to life. WOOHOO.. (H)

Just gotta find a thermistor now to replace this broken one..

BIG thanks to 84GKSIG. :thumpsup: cheers man.. Appreciate the help.

Now the lad can weld the cracks up in his JEEP... 8o|
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LukeAussie
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Re: Halp meh, Oh halp meh!!

Post by LukeAussie »

Good work! Electronics is always a bit of fun, particularly when you can't really see what's going on :) Thank goodness it wasn't one of the trannies (are we still allowed to call them that?) or an IC, as you can end up chasing your tail for yonks before finding the culprit!
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bruggz351
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Re: Halp meh, Oh halp meh!!

Post by bruggz351 »

I'd forgotten just how nice it is, just sittin quietly with the soldering iron plodding away. I'm dissapointed it's fixed :lol:

I'll have to go to Jaycar and find a project or something to do ..

I haven't touched electronics since high school. Apart from not being able to remember what anything is called I did alright. :thumpsup:
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