[GreenKeys] [External] Motor start capacitor

[Jones, Douglas W]

From: WAYNE via GreenKeys <greenkeys at mailman.qth.net> -- Thursday, January 29, 2026 3:18 PM
> sometimes the problem is the motor start relay is very dirty and pitted

See
-- https://homepage.cs.uiowa.edu/~jones/pdp8/UI-8/2026/01/22-TTYstartRelayGuts.jpg

I opened and inspected the relay, indeed there was a bit of scarring around the start contacts.  I burnished the contacts just in case, reassembled the relay and tested it in circuit.  It works just fine.

To test the relay, remove start capacitor, put ohm meter across starting contacts, briefly (under 1 second) turn on and off motor -- it won't spin, but you should see infinity on the meter when the power is off, 0 when on, and infinity again when off.  Use an analog meter, since digital meters are mostly a bit on the slow side.

            Doug Jones