Looking for a copy and service info for this model. thanks

The ETF has scanned the Riders for it - scroll down to RCA: http://www.earlytelevision.org/tv_schematic_diagrams.html

There's no photofact for it. Some indexes list set 78 folder 4 which is a Coronado model on the same chassis. It's somehat helpful and somewhat accurate, but not completely either.

I was checking out the sources I have and found the following sites:
http://www.earlytelevision.org/images/621_manual.pdf
http://www.earlytelevision.org/holden_621.html
http://www.earlytelevision.org/images/RCA-621TS-Rider-TV1.pdf

They look like they have all the things you would be looking for, to include one is a restoration already done. Hope it helps.