Oops. Yes, to answer some questions:

Yes, I got down to the mode switch and cleaned it. I also checked the belt. To be honest, it looks like someone was in here already. The switch looked like it had already been cleaned. I cleaned it anyway following 12voltvid's recommendations. The belt looked like it was recently replaced (albeit a bit greasy.) I cleaned both the belt and the pulleys. The retaining clip for the worm screw was broken, indicating someone had taken it out and replaced the belt already. The belt didn't seem to be dried out or goopy.

I took care to follow the service manual for aligning the mode switch V groove. The service manual says to push the plate assembly to the right and line up the holes on the plate assembly with the holes on the chassis, then insert a screw driver to keep the holes aligned. Then align the V groove on the mode switch.

Edit: Also, I'm in Northern California (South Bay Area). So if any enthusiasts are curious and want to see it in person. I could also stream it on Twitch, I have a web camera. I don't know if seeing it in real time would help.

You're too far away for me to help (or help make it worse!). You may want to contact NorCal715 on YouTube. Maybe he is in driving distance and could help you out. He says he's busy so it could take a while.
Maybe take a vacation to Vancouver. 12voltvids is there. LOL
It sucks that there is nobody left to work on this stuff. You have to learn yourself. Then there's the whole parts issue. At least some people have come up with ways of making gears, etc.

You could also try to see if Dave's TV & VCR Repair in Grant's Pass, Oregon would look at it. He's also on YouTube.

That's a 12 hour round trip drive. If I'm gonna spend $100 on gas, I might as well buy a different "known good" VCR.

I'm gonna try nudging the switch one direction or the other and see if it affects the VCR's ability to remain in rewind mode. Or maybe apply a tiny bit of pressure on the switch.

Thanks, I'll send him an email. Maybe I can at least get some advice or a new direction on how to troubleshoot it.

Try to get an oscilloscope .one may come up in your area.most goodwill hubs will let u pu from them save on shipping
https://shopgoodwill.com/categories/...=grid&ihp=true

I pu parts and test equipment at harvest usually cheap sometimes free
https://www.arrl.org/hamfests-and-conventions-calendar

I found a second 12voltvids video with a JVC unit with the same mechanism that won't rewind. It's also the second JVC related video where he does not revisit the issue with followup video with a fix. :(

https://www.youtube.com/watch?v=__PFQlKia68

However, there're quite a few helpful tips in the comments section. One user suggested it could be a warped "pendulum." I don't know where that part would be. Another user said their photoconductor had bad contacts and was causing noise on the signal, making it not rewind correctly, and offered a suggestion for a fix.

So I have some new avenues to explore for troubleshooting. Could still be electrical, but could also be a mechanical issue. I'm going to try to replicate what he was doing to get it to rewind reliably without a tape.

The noisy photoconductor has me intrigued, though, because I initially thought it was the sensor and seemed to get it to reliably rewind when I covered it. But then later it wouldn't rewind even if I did cover it. So if it's noisy, it could be that the first time I covered it, it was just enough to get it to work. Then it got more noisy the next day, and covering it wouldn't make any difference.

Anyway, just an idea.

Could also be the photointerruptor. I could test it by shining a light in there with my multimeter hooked up. See if it's detecting light. That would at least tell me if it's working, but won't tell me if there's noise on the line. I don't have an oscilloscope. They're just too expensive, and I have absolutely no idea how to use one.

Photointerruptors are fine as far as I can tell. They produce voltage when I pass a light in front of them while connected to my multimeter.

Dang it.

I wish I would have seen these earlier...

https://youtu.be/zh14W-bwoQs?si=0Ffl2xxWSJQOFS-F

https://youtu.be/BavHcSo7rRY?si=qCqR0V78lbScyMom

https://youtu.be/2fdfCQQszcE?si=8d52HKhe4L0AVSz8

Turn on CC - auto translate. It's pretty funny to see the words misinterpreted.

Oh ... my ... god. You may think you're late to the party with those videos, but look here; mine does NOT have this capacitor there:

https://youtu.be/2fdfCQQszcE?t=1426

12voltvid's doesn't have it either. But that Russian guy in the comments said he added a low value capacitor to clear out the noise on the sensor which prevented his from rewinding.

I don't have a 154, but I did have a 104. What's 50 nF between friends? I added the little capacitor there, and ... IT FREAKIN' WORKS! It rewinds!

I tried removing the capacitor and it resumed not rewinding. Reinstalled the capacitor and it now rewinds.

I can't believe this. An absolute stroke of luck.:banana:

Lost my right channel, though. Not from the capacitor. The wire got ripped in half. I soldered it back together and it worked for a while. Lost it again. I think I might be ripping the wire out on accident somehow every time I life up the mobo. :/

The one he is working on is for the Japanese market. That cap looks like it was added after the fact. Maybe there is a service bulletin for this issue.

Hopefully you get this thing working 100%!!