"Are there indexing marks/arrows etc in the mechanism , in case its
jumped a tooth? "

There are some. You have to figure it out though because in the manual there is no picture depicting "Setting condition" which shows you how to put it for reassembly. I got it pretty much figured out because I have a guinea pig, another VCR that is nearly identical. The goat...

I took the goat apart and found that the mode switch is full of nice grease and it is not even dirty, and it was treated much worse than the deck I want to fix. All the grease is good, and mind you this 780 works sometimes, it's just that after it warms up and/or goes through a few cycles it does this ****, and displays a bunch of different errors, most of which come back to either it cannot tell what state the mech is in or the unloading is incomplete. I have tested the mode switch with an ohmmeter and it is either a dead short or open depending on the position and which terminals you check. When it works it does not try to overrun the loading motor or anything of the sort.

The fact that it works sometimes leads me to believe the mech is fine. I started to try to trace the mode switch connections back to the IC but the double sided (or more) PC board makes that impossible. In fact it is more than two layers because the traces from the mode switch go to vias and then on the other side is solid copper, a ground obviously. there must be at least one more layer in between.

The print depicts IC 501 and on the board is IC 201. That is where the difference starts. The board.

I probably posted prematurely, I was going to somehow check the end sensors because they are involved in the loading process. But last night I decided to putz around with it and find the place where the mode switch actually gets to the IC. I'll need to test it on the actual deck I am fixing because the goat is all apart, and I found out that little plastic things break when you remove the mode switch. So I am treading lightly because I know most of theparts are unobtainium. And if it is the IC, not only do I not have the proper equipment to change it, I don't have it to get the replacement out of the goat, and plus it has the same problem,or at least it was found in the same state, tape stuck etc.

I might have to just say fukit and fix the 920, now that one IS dried grease. I have not worked on one but I am familiar enough to know the the grease on the one tape arm dries up and it strips the rack gear. Yes, one of those. So I intend to address that before even plugging it in. I got LPS2 which is so good it will do it without disassembly, but I would rather do it right, get all that goop out. The grease in the 740 (the goat for the 780) is in such good shape maybe I should use that.