FWIW: Can't speak to this mechanism specifically, but with many tape transports the brake band is used to apply a slight amount of drag on the supply reel to ensure proper tape tension on the supply side of the capstan.

If you mean the supply reel in a form of a band then yes, It would be an awkward engineering to use brakes to adjust tension on the take up reel, The take up spindle has already a felt pad built into it or the idler gear to adjust that tension, Even the OP referred to a youtube video in his first post about that.

Thats what I did the other days. Attached some pics of both pads. Its felt, but with some black coating on top that gets off quite easily. I first thought it was dirt... These brake pads are not even shown in the exploded views in the service manual! No part number. Strange, they seem to be a maintenance item as they clearly wear out.

Result of the swap was a decently working VCR, but I'm not sure whether that is due to the brakes or if there was something else. I now notice that the pads do indeed not touch the takeup reel in play-mode. Couple seems quite OK. I do not have a torque gauge, but when I hold it with my fingers it feels reasonable. Is there a quick-and-dirty method to check whether torque is in the required range?

The other VCR, the one that seemed to smoke a joint, is working happily since. I still have no idea about what could have caused it. Eventually one of the zillions of electrolytics went bad somewhere in a circuit I do not use when playing Secam to PAL...? Power rails are all good, so if it was an electrolytic it either went open circuit or it shorted out and charred a series resistor or a part of the printed circuit.

Does anybody know if there is a way to access the parts that are hidden by the RCA sockets on the output board? I couldn't figure out a way to remove the plate holding the sockets from the board except by desoldering all of them. Most of the remaining smell came from underneath that plate, but I couldn't see anything wrong looking between the boards from the sides.

cheers
Martin

Years back sony also maybe under zenith name
Had a pulley maybe 2" diameter with a string.
I assume used a tension meter,gram guage.
I couldn't find it on the web but there are sites discription

How to measure torque with a pulley and string.
Start with a hub out of a video cassette.
Add a pulley ..diy.project...
Maybe someone in the group is near u and would check
It 4 u....

Sure, if someone near or in Stuttgart / Germany wants to drop by, he's welcome!

I thought there might be some ways like how electricians measured voltage by putting their fingers on the wire... :-) Experienced VCR servicemen sure could judge the right couple with their own fingers.

cheers
Martin