How to / DIY > Engines

Lister LT1

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BruceM:
Weldherup, 50 V (DC?)  at the brushes should be plenty, but it depends on the rotor coil windings. The readings at the capacitors of 180V (DC?)  is inconsistent with 50V DC at the brushes if the capacitors are doing as Bob suggests.  There's a big difference between AC and DC volts in this situation, so I don't have enough info regarding measurements or schematic to add much more. Any local generator repair technician should be able to get this sorted very quickly if it's over your skill set.

I concur, Bob, on the date of manufacture of the electronics as no earlier than mid 70s.   Easy to reverse engineer and cheap to repair.
 






 

cobbadog:
Never ask me about electrickery but having just repaired a circuit board on my MIG welder today after 6 weeks of looking at it, finding issues with a diode, a small capacitor and finally the relay switch it is working again. While I was waiting for the relay to come on the slowest boat from China I spent a lot of time at the work bench with a desk lamp and a magnifying glass searching for suspect 'dry soldered' joints and found some joints I was not happy with so a quick touch with the soldering iron and a dab of solder and that was sorted. It was the use of the light and magnifying glass that found the capacitor problem and the diode was an obvious failure.
I used mineral turps to wipe over the board but my board did not have this wax covering. If you were here in Oz at the moment you could leave the board out in the sun and wipe off the wax as it gets the solar treatment but I am guessing you are near snow conditions soon so that is not an option. Acetone might be another option as to dissolving the wax but check with the guys if that would cause any issues.

BruceM:
Methinks you're being too modest, Cobbadog.  Repairing a modern MIG welder circuit board is a major accomplishment; I can't imagine how much magnifier and precision work that must have been for surface mount PCB rework.  Bravo.
Bruce

cobbadog:
Thank you for your very kind wordss but there would be no way I could have done it with out the enormous help from members on a welders forum who knew wha to look for and there for they guided me through the repair.
Yes, my electric soldering iron was like using a sledge hammer on a thumb tack but with persistence I got there.
The capacitor measured 2-3mm in length and close to 1mm in width. So small I 'borrowed' Dees tweezers from her sewing machine to place and hold it while I put a tack on one end.
I only had a go at what I was advised to do by people who have the 'smarts like you' on what to look for and do. I am proud that I actully did it but I do not understand what it is I did as electronics seem to avoid my b rain pettern and wont stay and allow me to understand them. As to have the ability to reverse engineer circuitry, now that is a true talent and IO tip my hat to those who can.

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