Jun 21, 2010

Electric Fencer - Southern States model 700

My dad gave me this one to work on and the broken rivets, disconnected wires and missing fuses made it quite evident that someone had attempted to fix it previously.

Upon pulling it apart I noticed this:
Here being the front of the same board
The circled burn mark is under the large thyristor, so something was either jumping across there or it was once a good connection that is now burned and open.

I called my dad (who had several of these yet declined to send me more than one) and he said that the burned area is supposed to be an open and not a connection.

So I wired in some fuses and hooked everything up and you could hear the transformers working and then shut off as things got hot, but never did anything click and work as it is supposed to.

I pulled the large thyristor and the two outside pins are closed in both directions and everything is open to the middle pin in all directions. I believe in a good working thyristor the middle pin is a gate and should be closed to one of the side pins and the two outside pins should act as a diode.
(the thyristor in my fathers fencer (also not working) acts exactly the same) So either both our thyristors are bad or there is some other problem I am overlooking.

1 comment:

  1. So after replacing several things like the large thyristor, resistors etc.., I could not figure out why power was jumping between the legs of the large thyristor,
    so I pulled the board and used its parts to fix several other similar fence chargers,

    I can say that the problem was the board as when I installed a different board it worked fine, so the capacitor and transformers were not at fault.