In this circuit, there is a wire between M5-1 and M5-3 (at the bottom). It's a little plastic connector with a wire in it that you can pull out.
I've been trying to debug a power issue after recapping this 1980's power supply. At first, I forgot to put that connector back. Some of the reading looked correct, but others were too low. When I added it back, the formerly-correct readings jumped to ~1.5x.
What purpose does this connector have in this circuit? Why would you want it connected? Why disconnected? Why isn't it just permanently there?
Best Answer
It's just mains voltage selection, quite common those days. It turns the diodes and the two 220uF capacitors in either a bridge full wave rectier for 240 V use (wire removed) or a voltage doubler for 115 V usage (wire fitted).