Just a follow up here and, I suppose, a debriefing now that the unit is back in working order. The fix for my initial issue (the relay was not engaging) had to do with the protection circuit. After I replaced the caps and transistors in this circuit, I was getting output to the speakers. The issue with the flouroscan display was resolved by replacing fuse F4, which was blown (likely due to my own careless probing). I used a small glass fuse puller to get that one out. It took a while to order the fuse puller, but it was 100% worth it. No need to wreck your project by trying to pry out a glass fuse and having it break.
As for the offset issue, well, I decided to leave well-enough alone. Offset readings are at around 40-50mV for the right channel, which is at the upper end of the "acceptable" scale mentioned in other threads. Left channel is fine. I tested the transistors for the right channel in circuit, which didn't reveal any glaring issues like a short. I also tested the resistors R332, R335, R336, but didn't see any obvious issues. I had suspected the driver transistors (Q14: 2SC1913, Q16: 2SA913) might be the culprit, since the readings I got were a bit different from the L pair. I might have replaced them, but I didn't find a
crystal clear answer on the forums for a suitable replacement. It seems like Toshiba may have made some replacements for a while, but no longer. The issue could just as well be with the output transistors, but I didn't want to pull them off the heatsink to test them. I'm interested if folks have thoughts about this.
I replaced the lamps with LED's as I mentioned above, and they really look stellar. As usual, the brittle tabs had broken off all my lamps, so I applied a
very small amount of super glue and some electrical tape to put them back in. They seem pretty secure for now. I'm aware that there are some suggested replacements for those lamp sockets from mouser in other threads, but I decided to go the lo-fi route. I may replace them soon so that I don't create a situation where the lamps fall out and cause a short. I also broke the original dial string on reassembly, so I ended up replacing that with a new nylon cord that I bought on eBay (for future reference: the .80mm cord works perfectly for this tuner). The service manual has very good, clear instructions on how to replace that dial string, and it wasn't nearly as difficult as I thought it would be to restring it. I also used deoxit on the pots, switches, and inputs. No noise at all from those pots now.
Here's a photo (can anyone spot the mistake I made on reassembly?)
As this was my first time attempting any repair like this, I thought I would at least document a few things I learned that I would have told my past self when I started this project. First, past self, don't ignore the very sage advice to build yourself a DBT. I built one, and it saved me at least once. Second, do a good thorough cleaning of the board before getting started. Use 91% isopropyl and an acid brush (take care to ensure good ventilation when working with isopropyl). Take your time, and inspect every component. Use it as a chance to familiarize yourself with the layout of the board, and pay attention to which transistors are in which spot.
Finally, past self,
take your time. I know that you really want your trusty old receiver to work again, but there's no need to rush. It's nearly 40 years old, so taking another week to properly diagnose an issue is well worth it.
Thanks to AK for all your help with this project! I'm already looking forward to my next project: rehabbing my mid 60's era Victrola-branded RCA console. I'd be much obliged if anyone could direct me to the service manuals for those units.