Cebora 802 contactor intermittent

[ChrisR]

Hi to everyone, I have had my Cebora 802 for many years now and never had a problem till during some welding the contactor started to jump in and out when the torch trigger was pulled. I looked for some advice and came across this excellent forum.
I checked that all the wires are tight onto the contactor and then put 24V DC, with batteries, direct onto the contactor and it pulled in just fine, so I don't think its a problem with that. It surely must be an intermittent 24V feed to the contactor, but I would be grateful if anyone has any ideas how to determine which unit/s are faulty.
I am no electronics expert at all and pcbs are a mystery to me, so any advice would be gratefully received.
One other issue I noticed on removing the torch from the machine was something that looked like arcing deposits between the torch and machine connector faces. Could this be something to do with problem. The torch is only a year old. Pics show the marks on the faces
Many thanks
Chris

 

[voipio]

Is that arcing, or corrosion on the connector faces? Neither is ideal.

The first thing to check would be the continuity of the trigger circuit between torch and connector. Ideally, use a multimeter, set to meaasure low resistance (typically set to the 200 Ohms range), with continuity buzzer enabled, and connect the multimeter leads to the small pins on the torch connector, using croc clip-ended wires. Press the trigger. The buzzer should sound. Now move the torch lead around, to see if there is any intermittency in the circuit i.e. the buzzer not sounding continuously. Also, vary the force, and direction of force, on the trigger switch, to see if it has any "bad" spots.

 

[Barking Mat]

Contact cleaner, and a small wire brush, clean it all up, and report back.

Welcome to the forum.

 

[ChrisR]

Thanks for the suggestions. I have confirmed that there is constant continuity between the torch and connector as the trigger is pressed and also have cleaned the connectors as suggested. Unfortunately the problem remains.
Having read previous posts on a similar problem, albeit not with the same model of Cebora, I'm beginning to think that the contactor cannot be getting a constant 24V to hold it in and this may be a problem with the PCB? I have checked it for visual signs of damage but can't see any.
I should mention again that I have no electronics knowledge so do not exactly know what I should be looking for or what the components on it are!
Thanks to voipio and Barking Mat for the prompt replies.

 

[Hutcho]

Check pcb for dry joints

 

[ChrisR]

Thanks Hutcho, to do this should I check for continuity across each component?

 

[voipio]

A visual inspection, with a good light, and close up reading glasses, or a decent magnifier, would help to find the most obvious dry joints. Normally, the solder will have flowed smoothly between the printed circuit board track and the component leg. Any solder joints that don't look like that, need closer inspection, and reflowing the solder, if necessary.

 

[Hutcho]

As above - take board out , anything that looks iffy (solder joint) just give the component a wiggle carefully and you might see the joint move - I would first check the connector block on the board as these are mostly under tension when they cable tie everything up .

 

[ChrisR]

OK I've checked as suggested and thanks for the in sight into pcb's. I've not been able to find anything loose or iffy looking soldered joints and haven't found any. Mind you with my experience I suppose I can't be certain!
What components should I check as I'm wondering if the fault is a component that's breaking down and a constant 24V is not being delivered when the trigger is pressed, hence the contactor constantly. chattering in and out
Thanks so much, this forum is great!

 

[Hutcho]

Try with the torch back in - knock tension off , then press the torch and wiggle it and see if it does it - I’ve had it on a Clarke where the torch connector was loose inside the panel socket

 

[ChrisR]

Finally got round to trying this but still the contactor is jumping in and out when the trigger is pressed. Think it must be a fault on the PCB and not delivering constant 12v to the contactor coil. Will see if anyone local can test the PCB for me
Thanks for all the suggestions as at least I have been able to isolate out any other likely causes

 

[eddie49]

The Cebora website for information about "Items out of production" :

https://welding.cebora.it/en/assistance/items-out-of-production?b_start:int=220

does have an entry for "Art.802", but there's only a parts list there, no circuit diagram. Anyway, in general even if there is a circuit diagram of the machine, manufacturers tend not to provide detailed schematics of their control PCBs. Then it's a case of reverse-engineering a diagram by listing the component part numbers and following the printed tracks.....

The machine in this ancient thread is a Cebora 802:

Help I have a MIG 802 and can't find out who made it

I have a MIG 802 mig welder that I acquired from a friend that found it somewhere. It is a european voltage welder set up for single phase 220 or 2 phase 380. I live in the US and need to convert it to us 2 phase 220. I am not electrically gifted so finding a US 220 transformer will be a...

www.mig-welding.co.uk

and the second photo shows what appears to be a Spot Weld variable time dial to the left of the wirefeed speed control. When enabled, the Spot option will release the contactor some time after the machine is triggered on. Check that this dial is set to zero, also wind the dial up & down a few times to "wipe" the potentiometer clean. At zero, is there a "click" switching action to fully disable the option? This potentiometer, or the logic on the PCB that it controls, may be faulty.