With that, someone with experience with US Betamax models, should be
able to help. I think most Sony Betamax players don't use rubber belts
or idlers.

Most Sony Beta VCRs are based on the "EZ-Beta" chassis, which has no belts
except one toothed nylon belt which drives the carriage. The advances, after
the tape is fully threaded by a motorized mechanism, is run completely with
solenoids.

But, there are variations of this mechanism, some which replaces the solenoids
with an advance motor, which is the case in models like the SL-HF750,
SL-HF2100, and the SL-HF2000.

A couple of models, like the SL-2700, uses a chassis that is somewhat similar
in layout to the aforementioned models but uses two independent brushless
motors for each of the spools instead of a single motor pendulum mechanism and
uses a regular belt which runs the mechanism that turns the threading ring in
loading and unloading the tape. The loading carriage is also driven by its own
motor, if memory serves me. (The carriage was also prone to breakage,
especially if cassettes were loaded into the deck too hard. Although this is a
common occurance to front loading VCRs even today, the carriage used in the
SL-2700 was especially sensitive to that.)

And, there are models, like the SL-5200, which use a completely different
mechanism. Then there are the top-loading Sony models which were the
predecessor of the front loading decks.

So, of course, we need more info from the original poster if he wants us to
give him more useful info. - Reinhart