Doug...

>Anyone with experience with the RA drive removal?
--------------------------------------------------------------------
Yep...just did that Valentine's Day this year.
(I see several responses already but one more ain't gonna hurt)

Removal and reinstallation of the 'goodies' is not difficult---BUT
the really tricky part(s) deal with the gearbox/hinge assy--STRONGLY
recommend you read Doc G's description/suggestions/comments on the
Dec motor at his website (I hard copied those pages).

Once you've got the OTA/Fork/base off the mount, disengage the
Dec lock and RA lock and lay the unit on a padded surface with the
base underside at a comfortable working level--control panel front
facing up and something on either side (base) to keep it from
rotating on you--more for convenience of working than absolute
necessity (unless you're a contortionist).

Adjacent to the all-thread input hole are two allen-head screws--these you
will remove first (the two larger allen-head screws slightly
above those two smaller ones are not removed.) The outer perimeter
screws are next removed and the base cover-sheet-metal can now be
removed. Note the white "grease" on the inside of the cover-plate-
DO NOT wipe off--this grease aids transfer contact between the power
transistors and cover-plate which provides additional heat-sink
surface area.

You now have an open/exposed innards of the base assy--I took a
Polaroid pix of this (I forget things easily)--note the plastic
cable connectors on the M/B--be careful when you attempt removal--
the plastic spring-locks on the sides of the connectors are hard to
see but must be released before the connectors can be removed.

Next comes M/B removal--note carefully where the 4 mounting screws
are located--there are 6 holes but only 4 screws--also, when the
M/B is lifted out, check immediately the backside to note where the
little plastic insulator/washers are--there should be a plastic
insulator/washer for each screw-hole ( 4 ). These, if loose, need
to be glued back in place so they'll be there when you reassemble.

The wide ribbon-cable can be flipped up and held out of the way
with a piece of masking tape--careful it doesn't pull loose and
slap you in the face.

You should now have a clear unobstructed view of the
RA gearbox/hingeplate assy. I did not remove the individual wire
cables from the RA gearbox unit---next, note there two allen screws
holding the RA gearbox/hingeplate assy to the top of the base...
the screw holes are elongated allowing a sliding-provision for the
assembly which in-turn affects tooth engagement and optimal
worm/worm gear engagement. Before loosening/removing the assy, note
precisely the action of the hingeplate--move it up and note how that little
_hidden_ spring pushes the worm back down to fully engage
the worm gear. Once you're satisfied with your understanding, you
can remove the two allen-head screws (Doc G suggests a l-o-n-g handle
allen wrench and I wish I had caught that initially--I didn't--and
as a result, I 'fought' myself until I got smart and let my 12-year
old grandson do the operation--my big, clumsy fingers!!

Once you do what you intended to do with the RA gearbox/hingeplate
assy, reinstallation is a straightforward reversal of that simple
removal.

The remainder of this msg will be simply excerpts from others who
were kind enough to send along their suggestions....needless to
say, READ EVERYTHING THRU FROM START TO FINISH BEFORE BEGINNING.
-------------------------------------------------------------------
FROM DOC G:

>Yes, I have taken several of these things apart. You need to be a bit
>careful but there are no traps built in to the control base.
>
>Besure you remove the screws near the central bolt hole and then the
>screws at the edge of the bottom plate. The central screws hold the
>heatsinks for the
>power transistors to the base plate which acts as a heat sink.
>Do not wipe off the white grease since it is part of the heat
>sinking contact between the transistor casees and the base plate.
>Then unplug the obvious plugs and unscrew the circuit board.
>This all comes apart rather easily.
>
>Now you will see the RA drive. Surprise!! it is just like the dec >drive.
You get two micro drives for the price of one. The only >difference is
that the RA drive has a little magnetic detector to
>tell the computer where the worm is.
>This is for the PEC drive synchronization.
>
>Mechanical problems are exactly the same as for the dec drive.
>Fix it in the same way by tightening the end play screw which
>may be the problem. also you can tighten up the slop in the
>platform motion a bit just as for the dec drive. If the problem
>is a loose gear within the gear box, and I hope not for
>your sake, a rebuild of the RA drive, just like for the dec drive
>might be necessary.
>
>Good luck -- Doc G
----------------------------------------------------------------------

>From Peter Eichenberger......

>Does the RA play show up without applying force
>in excess of what the normal scope weight would apply?
>If not, then this is correct operation.
>There is a spring in the RA drive that it designed to
>take up the slack in the gears. Normally, this is
>stiff enough so that the scope always rides on the
>same side of the slop; hence no backlash (from that source).
>
>-Peter Eichenberger
-----------------------------------------------------------------------
>From Paul Goelz...

>I generally sit out these drive discussions...... there are a lot
>of very competant folks out there and you don't need my additional >input.
>
>But in this case, I thought a little clarification/description might
>help.
>
>The motor and gearbox and worm all are a single unit, hinged so that
>the worm can move in and out relative to the main gear. There is a
>spring that presses the worm (and motor and gearbox) against the main
>gear, eliminating backlash. The hinge that the motor/gearbox/worm
>pivot on consists of two screws that can be adjusted so that there is
>little or no end float (side to side motion). The idea is to adjust
>out any end float yet have the pivot still be capable of free movement.
>
>With this understood, the possibilities for RA slop are: end float in >the
pivot hinge (most likely), loose fasteners in the RA assembly, end >float
in the worm gear shaft, loose or missing spring, or main gear >loose on the
fork.
>
>Like John said, dissassemble to reveal the RA drive and gears, lock
>the clutch and move the forks and see what moves. It should become >clear
right away where the problem is. Mine has no slop at all.
>
>Hope this helps!
>
>Paul Goelz
-------------------------------------------------------------------

Lastly, make notes, make drawings, don't be 'afraid' of it--
It "ain't" no big deal---just be careful and be aware that there
is help around "here"----and let us know how it went....

Hope this helps,
Gene Ducote (Charleston, SC)

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