I brought home a fence charger from the dump, hoping that it was there due to some simple malfunction that I could fix. On opening it up, I found no blown fuse or other obvious problem. I found the circuitry interesting: it uses a 7-bit ripple counter IC to count 60 Hz pulses, with a 64-count triggering an SCR to dump a capacitor into a high-voltage xformer. I.e., the fence is pulsed once every 64/60 seconds. The ckt is here:
The question is: where does the Vdd power come from? There is a 22u cap from the Vdd pin to gnd, but that's it. The trigger signal is a 5v 60 Hz square wave & is the only non-gnd connection to the chip. So, does this signal somehow, magically, charge the Vdd cap?
And ... it doesn't work because the chip does not count. The 22u cap passes a VOM test, but I didn't scope the Vdd pin. I concluded that the chip is bad.