I feel a little ashamed asking this question here, as it isn't really a proper electronics question, but not finding any better place to ask it, here goes. I'm trying to revive my trusty old electric drill (Craftsman
3/8" variable-speed reversible, all metal, not plastic, thank you very much). Years ago the speed control crapped out, and I ordered a replacement from Sears. When I put the new one in, the drill worked, but not very well: a lot of sparking from the brushes and erratic operation, like stalling and having to spin the shaft to get it running again.So far as I can tell there's nothing mechanically wrong with it. Like a lot of things from the past, it's built like the proverbial brick shithouse. I cleaned the commutator; the brushes are solid and clean, bearings well-lubed and free-spinning.
I think I just screwed up wiring the damn thing together. I have no diagram, and followed what I *thought* was the way it was originally, but apparently I've done something stupid.
The way it's wired now puts the field and commutator in series, which I believe is correct for this type of universal motor. I tried reversing one set of connections, but that didn't help, or even seem to make much difference at all.
Does anyone know how these things get wired? Anyone have a wiring diagram for this, or similar, drill?
Any help appreciated.