Cebora Pocket turbo 130 electrical trouble

[RobinForge]

Hi folks. After 30 years of trouble free welding my MIG has finally thrown in the towel! Hopefully someone may be able to give me some pointers. It started with the contactor chattering a bit. On inspection the contacts were badly burned so after studying various threads on this excellent forum I got a new contactor thinking it would solve the problem. It didn't. It turns out I don't have 240V across the two little contactor coil feed wires. Most things seem to check out Ok. The wire feed drive is fine. I get continuity from the machine end of the torch trigger wire to the contact tip when the trigger is pressed. I stripped the brass block in the trigger and cleaned the contacts on the trigger plunger. I've checked all the connections, a number of the spade connectors on the switches were a bit loose so I've replaced these. So far as I can tell, and I'm not a welder engineer, the only thing left to suspect is the PCB. However, the little relay on the PCB seems to click in and out fine when I pull the trigger. But, the new contactor remains dead. I've tested the new contactor off the machine and its fine. I would be really grateful for any ideas on this one. Thanks.

 

[mike 109444]

Are you sure the original contactor coil IS a 240 coil as some of the cebora schematics show 24Vac feeding the contactor ! That would stop it working.
The relay on the pcb may be for the feed motor but if it only feeds power to the contactor coil then even though it is operating it may have dirty/pitted contacts so may not pass power.
And welcome BTW

 

[RobinForge]

Thanks for the welcome and for your suggestions! Yes, the contactor is a 240V one, I checked this out right at the start. I will take a look at the contacts in the little relay on the PCB, though i'm not sure that relay can be opened up and fettled. You may well be right that it serves the feed motor anyway. In which case, I'm still no nearing finding a solution. Maybe I just have to bite the bullet and buy a new PCB, fit it and see what happens. Everything else seems Ok, so by a process of elimination I think the PCB has to be the suspect.

 

[mike 109444]

Seams a bit strange that the original contactor was "chattering" (as in it was receiving power) and you fitted a new one that does not have power to it's coil !
If you follow the two thin wires back from the contactor where do they go (pcb?) Can you post some pics of the pcb both sides.

 

[RobinForge]

Thanks for the comments. Just to clarify, the contactor went from working Ok to chattering and then to dead. I will post some photos this evening and will double check function of both old and new contrctors off a 240v source.

 

[RobinForge]

So, the contactor coils are fine across a 240v supply. It' definitely the feed to the coil that's duff. The coil feed wires are a pink wire and a black/brown wire. The pink wire comes off the 1/2 voltage switch centre posts and goes straight to the contactor top coil terminal. The brown/black wire comes off the min/max voltage switch centre posts and is switched through the PCB before going to the contactor bottom coil terminal. You can see it connects into the PCB on the cream plug connected into the side of the PCB in the photos. First photo - general layout of internals. Second photo - back of PCB, in position. Third photo - 'front' of PCB after unscrewing from control panel. The black and red feed motor wires and the torch trigger wire are the other connections on the top of the PCB. Any thoughts gratefully received!!

 

[mike 109444]

As the power to the contactor is switched by the pcb (almost certainly the relay) then the power should be there BEFORE the switching. If you meter for 240Ac with one meter lead at the Pink (1/2 switch) and the other test lead at the INPUT to pcb Brown/black wire (min/max switch). There should be 240Ac for the pcb to switch !If power is going IN but not coming OUT then follow track for Brown/black on pcb and you should find it goes to relay.
If power not present at switches then one or other could have burnt contacts (try flicking switches back and forth may temp fix)

 

[RobinForge]

Thanks Mike. I had the same thoughts. I have 240V into the PCB, and across the relay with the trigger pressed, so the relay looks Ok. But, the output from the PCB is still dead so I am guessing its a component on the PCB after the relay that's died. New PCBs are no longer available but I found a guy on ebay who offers a repair service so I will give that a try. Thanks again for all your assistance.

 

[mike 109444]

Can't see it being much that has failed as there is not a lot on the pcb!
Hope you get it sorted if not then return here.

 

[130]

If you have 240 volts across the relay with trigger pulled doesn't that mean that the relay is not working because if the terminals are connected there should be no potential difference? Or am I coming in from the wrong angle.

 

[RobinForge]

Finally sussed it out. It was indeed the relay on the PCB after all. I've cleaned the contacts and adjusted the gap and now its getting a good reliable contact it works fine again. I think the reason the contactor was chattering originally was because the PCB relay was chattering due to the relay contacts being burned and creating an excessive gap.

So, all sorted. Not sure how long it will last and I guess a new PCB relay is on the cards before too long.
Many thanks to forum members for advice and suggestions.