I have some questions concerning my U.S. Tower MA-770MDP motorized tubular
crankup. Comments would be especially welcome from anyone with a U.S. Tower
motorized tubular tower with positive pull-down -- MA-550MDP, MA-770MDP, or
MA-850MDP.
Ever since I got the tower last year (new), I've had problems with the
pull-down side of the cable popping off the upper two pulleys on which it
rides when the tower is fully extended and sways in a stiff breeze (say
15-20 MPH). When it does this, I can reach up and swing the cable back onto
the pulleys. This can only be done when the tower is fully extended -- when
it's lower, the cable is too tight to be moved back onto the pulleys. It's
clear that the cable is not tight enough when the tower is extended, and I
have information from U.S. Tower and KJ6Y about how to tighten it up (the
spring is fully compressed, so I have to loosen it and use a come-along to
tighten the cable at the top bracket to which it is secured.)
However, there's something else that doesn't look right. The three pulleys
that the pull-down side of the cable rides on are not perfectly in line
with each other or with the top bracket to which the cable is secured.
Looking up from the bottom of the tower, the middle pulley is to the left of
the lowest pulley, the top pulley is to the left of the middle pulley, and
the top bracket it in line with the lowest pulley (i.e., it is to the right
of the middle and top pulleys.) This is causing the cable to ride over the
top and middle pulley at an angle -- in other words, the cable is not seated
perfectly in the pulley grooves. I don't think this is normal and I think
the misalignment is contributing to the problem where the cable pops off the
pulleys (the misalignment results in a rightward lateral force on the
cable.)
I think this alignment is abnormal because when the tower arrived, I noticed
that the cable had pulled off the top pulley and was wedged between it and
the bracket. However, the cable popped right back into the pulley groove
when we moved the tower to unload it. I suspect that the top pulley bracket,
or perhaps the top bracket to which the cable is secured, were bumped during
shipment, causing the cable to pop out of the top pulley and causing the
present misalignment. The cable was probably too loose (note correct
spelling) as well. The first time the cable popped off, I didn't realize I
could just swing it back onto the pulleys, so I lowered the tower, tilted it
over, and fixed the problem by removing the middle pulley bracket and
sliding the entire assembly under the tight cable. I realized then that
there is some play in the positioning of the pulley brackets on the
circumference of the tube. I tried to line up the cable in the middle pulley
as best I could, but I couldn't get it to lay perfectly in the groove. I
suspect that this is because the pulley above it or the top bracket have
been knocked out of position.
So, my questions are: 1) Are the pulleys and bracket on your tower in
vertical alignment with each other? If not, what is their orientation to one
another? 2) What path does the cable follow on the tower? On mine, it goes
over the outside of the lowest pulley (i.e., the pulley is between the tower
and cable), over the outside of the second pulley (again, the pulley is
between the tower and the cable) and on the inside of the top pulley (the
cable is between the pulley and the tower.) Is that how it goes on your
tower? 4) Does anyone know if the pulleys and brackets are deliberately
positioned out of alignment (say, to put some kind of twisting movement on
the top section to prevent it from binding on the way down?)
Seems to me that I should loosen the cable and try to move the two middle
pulley brackets (and possibly the top bracket) into better alignment with
each other so that the cable lays perfectly in the pulley grooves. Then, I
should tighten the cable as described above. What does everyone think? Ask
U.S. Tower? Well, last year I tried to ask Bruce about it but couldn't get
much of a straight answer other than instructions about tightening the
cable. I'm going to take another go at it this year, but those of you who
have tried to get technical info out of U.S. Tower know just how much I'm
not looking forward to that experience...
Any help from Tower Talk would be much appreciated.
73, Dick, WC1M
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