Enco 9x20 Won't Run In Reverse

I have an Enco 9X20 that was made in 1988. I've owned it about 6 months and have used it a fair amount. The other day I was turning some Delrin rod to size and was stopping frequently to measure diameter. One time after taking a measurement I went to turn the lathe back on and accidentally turned the switch the wrong way (to the reverse position). Nothing happened. The motor just hums.

I'm not particularly good with electronics. I can solder, check for continuity, measure resistance, but...

Enco 9x20 Won't Run In Reverse