Thanks for your information, it’s infuriating, it worked great.Hello and welcome to the Forum !
I suspect that there is a fault on the PCB in the spot/stitch/burnback circuits. I am not aware of a circuit diagram being available.
The early BOC/Murex machines were very well designed and used high-quality components, but suffered from poor assembly work and quality control, especially the soldering on the printed circuit boards. As in the other Transmig thread:
https://www.mig-welding.co.uk/forum/threads/transmig-140-pcb-component-values.98793/
the way to start is by looking for contact problems at all the push-on tags, the plugs & sockets, the screw terminal blocks, and finally re-flowing all the solder joints on the PCB.
Obviously, do the work in sections, and make a note of where everything goes before starting.
I should have mentioned that since the small relay on the PCB controls the bigger Contactor, check if that relay opening precedes the Contactor dropping out. If it is not obvious, you could remove the plastic case and hold the relay shut. It is unlikely that the Contactor itself is faulty.
Sorry to be a nuisance, yet again.Thanks for the update, and I'm pleased that your Transmig is working again.
sorry to seem ignorant, down to no experience, can you tell me which is the rectifier?No spark /arc = too low welding voltage.
Test the diodes on the rectifier with a DVM set to diode test mode.
Each should read above 0.5 one way and 0 / 'OC' the other.
You may well find one or more of the diodes have died.
The brand name is "Powerstat", the manufacturer is The Superior Electric Co., Bristol, Conn., USA.variable transformers both made in USA. I doubt if spare carbon brushes are available. You would have to make them