a few years ago I did a page about a rogers restoration I did, the link is here
https://members.shaw.ca/philsvintageradi … ojects.htm.
Part way down there is a link that says "troubleshooting the R771" Sorry but that page is messed up and you need to scroll sideways then down to read it. but there are some pictures of the chassis underside. This one had rotten rubber wire that was colored. I used a combination of rubber wire, and for the colors I couldn’t find, I used heatshrink over PVC wire. I am guessing that yours might be a year or two newer.