Yamaha kx670 tape stopping.

[ants2au]

We have all seen this problem. Always ends up being the spool reflector getting dirty etc.
This is puzzling though. I pulled the spools out. The black breakers are there. The infra led is lighting, and I have 5v when the beam is not broken. If I cover the sensor, it goes to 0v..so it can pulse.
But when I put any shiny surface against it, including the spool, it's being covered and won't reflect when the shiny part goes past.
If I move it out a bit (not the right position obviously), I can make it pulse.
It's like it needs more of a gap between sensor and spool...what do I do???
What else could be wrong with this setup?

 

[ants2au]

OK, so I got desperate, and had a junk deck which had good shiny spool reflectors. Put them on, and now it ff and rew all day.
But it won't stay playing...it will play for a sec and stop.
Does it have some sort of torque sensing?
It's def not using the reflectors to sense motion when in play..does it use something else?