Working on a very old Thompson Controller. Elevator goes into leveling, relays C1, C2, C3..... Drop out, unit hits final leveling and the motor stalls out. field voltage drops to 26vdc and resistors turn cherry red. Don't have a print, have checked for mechanical binds, seems ok.....unit seems worse in the down direction, runs a bit faster in up. No generator on this job, DC supplied to disconnect from rectifier in basement of building....very old set up. Unit has run ok for 8 years, that I have had it. Any thoughts?