I have two transformers that I have not used in 20 years. They worked when last used. How do I clean them and get them to work?
I would start by inspecting the cords to see if the insulation is ok. Then I would plug them into an outlet strip with an on/off switch and a circuit breaker with the switch off.
I would then plug the outlet strip in to the house outlet,turn it on and wait. If ,after a while, the transformers show no signs of catastrophic failue i.e. sparks and smoke, then move the voltage tap and check the voltage at the binding posts with a VOM. If you get reasonable values, between 0 and 20 volts, I would say the transformers are probably good to use. But always mount transformers in plain view, never out of sight. Always plug them into a cicuit breaker protected outlet strip. Never, ever leave the room while the transformer is energized. Turn it off at the outlet strip or unplug it from the wall. hope this helps…
Overall
I would take them to an authorized service shop, train store, small appliance repaire shop. Don’t tke chances.