Archive of the former Yahoo!Groups mailing list: Mellotronists

For those who like to tinker I'll post the progress on the Chamberlin
rebuild...

The proper operation of the M1's tape playback is wholly centered on the
tug-of-war between two opposing forces: the pinch roller and the capstan
versus the tape return pulleys on their opposite-rotating shaft. The return
pulleys slip on the spinning return shaft, so when a key is down the pinch
roller is supposed to completely overcome the pulley's desire to move along
with its shaft and pull it in the opposite direction.

These pulleys consist of a white plastic wheel with a big hole in the
middle. The pulley is about one and a quarter inches in diamater, and the
hole in the middle is maybe 3/4" wide. The hole is lined with a piece of
white felt so that the actual I.D. is more like half an inch. There's an
allen setscrew inset in the wheel from the outside that pushes on the felt
when you screw it in, allowing for friction amount adjustment.

I realized a couple of things after messing with the mechanism a few times.
I backed off all of the allen screws, so the pulleys were at their minimum
friction settings. Any that didn't rewind I would re-adjust. Well, some of
them were still stickier than their pinch roller liked, so there was no
getting around the warble. First realization: M1's that sit on their side in
a road case for years get sticky pulleys. Second realization: If at most one
pulley sticks, they all gotta come out.

The tape return shaft is a polished steel shaft much like a capstan, only a
little smaller (like 1/2" diameter). It's held at both ends by ball bearings
which are entombed by many hard-to-reach nut-and-bolt assemblies, thereby
frightening any would-be Chamberlin mechanics. Fortunately (and this is part
of the fun with these things) further scrutiny revealed that by loosening
enough setscrews the whole shaft could be gently pounded sideways out of the
bearing races and all the pulleys would thereby fall on the floor. Well
there's old carpet in the garage so it was OK.

I had to pop the rivets on the pulleys (yes they're press fit) and remove
all the tapes first. I left them attached to the anchor bar on the other
end, and wrapped them all around the bar and set the whole thing aside for
now. They look like they might actually be in pretty good shape.

Some of the pulleys were kinda tight. They were all pretty dirty. Remember I
said they were lined by white felt? What I meant was "white at one time".
Maybe Harry/Richard planned it this way? Some kind of maintenence indicator?

(keep in mind that all of my workbench activities are fairly short in
duration - kids in the bath, wife went to Brownie meeting, etc. - and the
rest of the time I think about this stuff even while I'm pretending to
listen to my wife so I have plenty of time to come up with my next strategy)

I figgered that if the pulley is too tight, and the setscrew is all the way
out, then the felt is too thick, so it has to be thinned. So I rolled up a
piece of 220 sandpaper and stuck it into the pulley hole, and went at it for
a while. By trial and error I was able to get the pulley down to where it
slipped on the shaft easily, and could be adjusted to be a tight fit.
Another realization - this times 35 was going to take a long time! After
some more thought, one birthday party for a 5-year-old, several workdays,
and more thought, I had the chance to go back into the garage and stick a
piece of sandpaper onto a piece of scrap dowel and chucked it up into the
drill press. I did all the pulleys in half an hour.

Next step - reassembly. I'm thinking I may want to lightly lube the pulley
shaft first. A thin coat of tri-flow maybe?

- Gene

M400S #1023
M400S #1213
M400S #1289