On Wednesday, April 18, 2012 12:33:16 PM UTC-4, hr(bob) wrote:

have you looked at any working mechanisms to see how/what sequence
they work?

Oh, of course! What I'm confused about is that the back tension arm is completely disconnected from the gears driven by the cam motor, which make pretty much everything else move except the direct-drive spindles and capstan.

The back tension arm is totally separate from all of the other moving parts in the machine. It's a thin metal arm that pivots on a tiny little rod connected to a thing in the front called the "STD ASSEMBLY" (standard assembly I guess?), which contains a tiny circuit board. The service manual indicates that the standard assembly needs to be placed pretty precisely (it gives detailed instructions for how to move it), and it says the voltage on a certain test point should increase linearly as the tension arm is pushed toward the front. This indicates that the system can at least measure how far the arm has moved, but...does that also mean it can apply voltage to move the arm toward the front with a tiny motor? I can't see any such motor, if it exists. Or is the arm meant to be pushed by the left shuttle or pulled by the tape as the source reel pulls tape in?

If anyone's interested in helping me figure this out, you can take a look at the service manual for the deck he http://www.digitalfaq.com/forum/vide...nual-sony.html
The forum requires you to make an account to download the manuals, but it's just a forum account, nothing shady (it's a bandwidth-saving measure, as well as a safeguard against the paywall service manual sites just downloading them all with a bot and reposting them on their sites for money).

Your question is kind of ironic though: Since the rest of the gears slipped teeth as a result of the jam (but probably not as the cause), I decided to take apart my unit and retime the gears according to the service manual. Unfortunately, I've apparently only made things worse. The mode gear, FR gear, and pinch communication gear are all perfectly lined up with the timing holes (although the mode gear and FR gear have a centimeter or so of un-notched, smooth-turning leeway in the unthreaded position, where it's tough to tell exactly how they line up, even with the holes...hard to explain). Manually cycling the worm wheel works fine (as long as I manually move the back tension arm out of the way with my finger), but the VCR keeps immediately timing out now trying to unthread when I turn the power on...even though I've double and triple-checked that everything's already in the default, unthreaded position. I doubt the mode switch is having problems, since it's electrical (it operates via optical sensors shining light on reflective paths on the back of the mode gear)...so clearly I've mistimed something, but I'm not sure how.

Two of the gears (the ones for the shuttle arms) look a little different than the service manual indicates, with different arrow locations and all, so the instructions for aligning them were a bit...unhelpful. Still, I think I have them aligned correctly, since there seem to be only three remotely sane positions for them relative to each other, and I chose the middle one. Besides, the cam motor doesn't even turn the worm wheel far enough for those to enter the picture before the VCR shuts off, so...I'm kind of at a loss. I'm tempted to buy another one just to see how it's supposed to work!