Cebora Boxer 185 info

[Landis]

My trusty welder packed in this morning and I'm struggling to find any decent information about it. It's a Cebora Boxer 185 (ART 534)

I've done some basic tests on it and I'm pretty certain it's a problem on the PCB but I've completely failed to find any information, wiring diagrams for the welder or a schematic for the PCB. The welder is not even listed on the Cebora site in their parts lists.

Can anyone give me some pointers ? I'm more than capable of fixing the PCB if I can figure out what's wrong with it. Looking at the PCB and tracing it manually it seems as if there's a problem with the low voltage circuit that would normally supply 24v DC to trigger the on board relay through the torch switch - there's no power at all to the switch and then the relay. If I short the relay contacts on the PCB the main transformer and gas solenoid are activated via the circuit breaker but no wire feed as I assume that's fed from the low voltage circuit too.

It looks like the low voltage circuit is a simple transformer/bridge rectifier/smoothing setup all on board the PCB so I'm assuming the problem is in there, particularly as what I'm guessing is the primary winding on the transformer looks to be open circuit - with no circuit diagram it may be that I'm testing the wrong pins although what I'd guess is the secondary winding is showing about 40 ohms which is reasonable.

 

[the snooper]

if the aux transformer is showing open circuit it has to be that, check it has power going in, if so you've found your problem, also there are a lot of smaller machines that use power from the welding circuit to run the wire feed motor so worth checking the circuit to check if yours falls into that catergory

 

[Landis]

After unsoldering the transformer and finding a pin out on the RS site it looks like my assumption regarding the pins was correct and it is indeed open circuit. New one ordered from RS so hopefully will have it back up and running in the next couple of days
There does seem to be some form of power feed back into the low voltage circuit from the welding output, I guess this puts some sort of "boost" into the wire feed at higher power settings as it seems to feed through a huge diode into the same low voltage circuit that the transformer feeds into.

For reference, I've ordered this transformer from RS (part number 732-0358):
http://uk.rs-online.com/web/p/pcb-transformers/7320358/?searchTerm=732-0358

I'll confirm if it works OK or not when it's fitted !

 

[the snooper]

the small transformer on the pcb isn't powerfull enough to run the wire feed

 

[Landis]

the small transformer on the pcb isn't powerfull enough to run the wire feed

OK, that makes sense then and explains the size of the diode they've used ! Thanks for the insight.

 

[NotANormalCoder]

Most of the MIGs in this class save the cost of a decent sized auxiliary transformer, instead they use the supply from the welding output (either AC or DC) to provide the power for the wirefeed motor. That's why there is only a small transformer on the board. This powers the trigger relay and electronics, so when you pull the trigger, the first thing that happens is the contactor energises, supplying power to the large transistor on the board. The electronics then regulate the speed of the motor. On some machines, this method provides a sort of 'synergic' effect, where the motor speed increases/decreases depending on the voltage output setting, so adjusting the wire speed is often more a case of fine tuning it to suit the voltage. Machines like the Cebora range regulate the speed accurately, whereas small SIP machine make no real attempt to regulate the speed, which is why the can sometimes be difficult to set up, as the welding voltage varies wildly depending on welding condition.

Just thought that this info may be helpful to others.
Dave

 

[hunter27]

Does this help at all ?



Pete

 

[Landis]

Thanks for all the responses, I now know a LOT more about the inner workings of my welder !

New transformer arrived from RS this afternoon, fitted it and now all seems to be working fine Only did a few test welds on a bit of 3mm scrap but all looks good. I hadn't noticed before but might be worth anyone else checking who has a similar problem in the future - the power LED on the front of the welder is driven from the low voltage circuit so if you turn the welder on and the fan runs but the power LED doesn't come on then it's a fair bet that the problem is around the low voltage circuit on the PCB. I'd noticed it wasn't on when the welder stopped working but couldn't remember if it was supposed to be on all the time or not - it is supposed to be on when the power is switched on.