Service info for the RP-190 record changer is available in the 1951 Beitman's book starting on page 111. It's available for free download here:
http://www.americanradiohistory.com/Beitman-Manual.htmMake sure you do the adjustments in the order shown in the service info.
I reccomend getting the idler wheel and cycling cam resurfaced at
https://www.thevoiceofmusic.com . He also has the rubber motor mounts, the chassis mounting cones, and an assortment of cartridges.