Slide Cube Projector Repair

The following document was sent to me by John Wardlow. It describes his experiences in fixing his projector, with the help of a repair technician.

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	John is an engineer in Texas who is trying to repair his Slide Cube
projector himself
	Derek is an experienced technician in Canada walking him through the
repair procedure

	John: Derek, I'm looking to see if you have an obsolete B&H "slide
cube" projector slide advance motor.  The motor is a small "slot car" type
motor.  Do you have any leads on where I might be able to locate the motor
or perhaps a used projector I can get to motor out of? Any assistance or
direction you can give me would be appreciated.  Thanks

	Derek: Hi John- I just got in a "Junker" but haven't had time to
evaluate the parts.  I believe the motor is working though.  As I recall the
user had shaved away parts of the turntable in a misguided attempt to
improve transport and I can't get a new one.

	(The caveat...of course, any advice I give you below is for your
guidance only and I take no responsibility for your ability or inability to
do any of the procedures safely or to obtain desired results..etc, etc.)

	Let me qualify something first though.  Are you certain that it is
the motor that is at fault (I've only seen one die before) or is it the
teeth on the little (black, or white) gear that it drives and that engages
the turntable? This is more common problem.  To check the gear (if you
haven't) lift the top cover to expose the turntable.  Note the little silver
"finger" that is resting in one of the slots on the side of the turntable.
When you reassemble, you'll want to fit it in again like that; doesn't have
to be the same slot.  Now, with a tiny screwdriver, pry off the c-clip in
the middle of the turntable, note and remove the tiny black washer, then
lift the turntable straight up at the 1:00 o'clock position is the little
gear.  check the condition of the teeth.  This gear is still available, but
I don't know the source.  There is a company in nearby Toronto that gets
them but they cost a fortune.  If needed I can direct you later.

	Now, if you've already gone past this stage and are into the "guts"
inside, I'll assume you've diagnosed the motor correctly.  (Check that there
are no loose wires) While you're in there, look essentially in the middle
and you'll see a locking nut on which the shutter blades pivot.  This
eventually gets sticky as the lubricant dries up.  If you feel adventurous,
you can disassemble the shutters, clean off the old lubricant and use a very
light grease in small quantity when reassembling.  If you don't have a very
light grease, no grease is preferable to heavy grease.  If you do this, note
carefully the shape and orientation of the two shutter blades.  They are not
identical.  Also note their position under a crescent shaped metal guide at
the edge of the shutter blades.  Remove the nut, then gently lift the
shutter blades, one at a time.  Note a small plastic washer under the first,
and usually under the 2nd shutter blade arm (at the pivot point).  Note the
order in which they all come off.  Clean and, if possible, re-lubricate the
pivot points.  Reassemble.  Tighten the nut down to the point that there is
some friction, then back it off a little.  You don't want to bind the
shutter mechanism.  This is all to stop the projector from "skipping" slides
and/or jamming.  (They often jam paper mount slides anyway)

	When re-assembling the projector, there are 3 things to remember: Be
absolutely certain no wires are pinched between the casing and the mechanism
or inner casing.

	It WILL fit together, though it will not appear to until you are
very, very frustrated.

	Do not swear in front of the children when reassembling.  You will
want to.  

	Now, after all that, if you are certain it is the motor you need,
please get back to me and I'll double check the motor I have and fix a price
and mailing costs.

	John: Derek, I took it apart further, though I wished I had waited
to read your email as I discovered many of the things you mentioned on my
own last night.  Yes, I attempted to remove the black lever.  I loosened the
mounting screws of the solenoid and finally determined, as you pointed out,
the black lever was not worth removing.  It appeared to move back and forth
fine, but now the unit really 'buzzes" when I push the slide advance button.
I'll tweak the solenoid position to see if I can get it quieter.  

	Derek: That should do it.  You'll have to experiment a little.  Look
for any tell-tale traces of the original position, made by the washer under
the adjusting screws.  Use that as a starting point.  It's a pain to have to
partially reassemble and test and repeat.

	John: There also seems to be an adjustment of the shutters that I
haven't quite figured out, but there is an elegant design of an cam adjuster
connecting the metal shutter arm to the black lever.  

	Derek: I call it the eccentric, below.  You don't want to touch

	John: I suppose if I ever get to the point of getting the turntable
to turn (and stop) smoothly and consistently, I'll be able to appreciate the
meaning of that adjustment.  

	Derek: All things being equal, and the shutter blades assembled
correctly and closing properly(see below) the eccentric adjusts the blades
so that no light shows through when closed.  Very unlikely to need

	John: I learned the importance of that black lever and the switch
position, this seems very critical (the first time I tried it after
reassembly, the table just kept rotating).  I think I have the switch
position adjusted properly now, so the motor shuts off just as the "finger"
begins to slide into the slot.  

	Derek: You've been having a lot of fun haven't you?

	John: I found a potentiometer limiting the current to the motor so I
cranked this for highest motor output and that helped immensely.  It still
rotates slowly and inconsistently, so I think a new motor and new
potentiometer would help.

	Derek: Hmmm...Are the shutters opening/closing easily now? The
locknut can't be too tight.  One point of friction that MAY be a problem is
where that eccentric meets the silver lever that pushes the shutters.  While
I wouldn't advise adjusting the eccentric, if you can lift the eccentric
carefully to disengage it, clean the little silver "nub" that goes into the
eccentric with solvent (WD40 is fine) on a Q-tip.  See if you can get a tiny
bit of WD40 into the "cup" of the eccentric.  Again this is usually not a
problem area, but you never know.  As for the potentiometer, it's unlikely
that it would need replacement unless you are getting irregular gain from it
i.e. good contact/poor contact at different points.  

	John: The "finger" that is connected to the black lever sometimes
sticks halfway in the slot so the shutters don't open completely.  I cannot
find any additional source of friction in the assembly so I pulled the
return spring and hooked it on the tang a few coils down to give it a little
more force, but this may be contributing to the solenoid "buzz" problem.

	Derek: I've had to do that sometimes too, but I'd turn the
potentiometer down a little.  Again, only once in a while, do I find one
that needs to have the silver "finger" turned ever so slightly from side to
side to fit into the slot on the turntable.  I do not recommend it as you
can get it more out of whack than before.  But it may be a last resort.  Get
the speed down a bit and that should do it, assuming mechanism is not
binding somewhere.

	Just thought of something- when the shutters close, is there any
light showing through? If so, try putting the blade that overlaps the other
in position so it is under the other.  They may close more fully that way.  

	John: I really have a lot of respect for guys like you that work on
these elegant mechanical systems.  Everything must be timed and adjusted
just right or they become temperamental, but that is the way machines like
these were possible before digital sensors and timers.  It's kind of a fun
challenge for me to see if this mechanical thing will beat me.

	Derek: Frankly, I hate working on them.  They were a good concept,
poorly executed, with quality of parts and assembly going downhill the last
few years of production.  

	John: I'm going to work on it some more this weekend.  Thank you for
your excellent advise.  I'll be writing you again when I've done all the
damage...  that is...  I have explored it further and have decided what to
do with it.

	John: Well, the projector works like new now! 

	Derek: Glad to hear it!

	John: I located the source of the friction in the turntable
assembly.  It wasn't coming from the turntable itself, it was coming from
the motor & gear assembly.  When I originally reassembled it, I used
moderate force to push the motor up against the plastic reduction gear.
Since this gear has been referred to as the "Achilles heel" of the projector
I was attempting to minimize tooth clearance and any premature gear wear.
This preloaded the bearing surface between the gear and spindle causing a
large amount of friction.  I loosened the motor and reassembled it using
light pressure on the motor and that speeded things up a lot.  I also
discovered that the projector itself contained a "spare" motor.  I found an
identical motor in the autofocus assembly.  

	Derek: That's a new one on me.  It never occurred to me.

	John:  Since this had only a fraction of the mileage and load of the
turntable motor, I swapped them.  It may not have been necessary, but it
couldn't hurt.  The autofocus motor required a good "solder sucker" to
remove the pool of solder from the PC board holding the motor's solder tabs.
The turntable now turns swiftly and smoothly.  Keeping the turntable at a
constant speed, I found, is key to keeping the timing of all the mechanicals
just right.  After working on the switch timing a little more and
readjusting the solenoid to remove the buzz, the projector works flawlessly.
I did find that the spring still needed to be stretched and reattached a few
coils down for consistent reliability.  The spring may have lost some of its
force from being stretched for so long.

	Lesson's learned:
	Don't apply much force on the motor to the gear when installing the
	Don't apply much force on the motor/gear assembly to the turntable
when installing the assembly
	Don't ever, ever bend the finger that slides in the slot.  Be
assured this is not the problem.  It will work when the motor speed and
switch timing is correct.
	The timing of the lever switch that controls the motor is very
critical.  It is adjusted like "points" are (were) in a car's distributor.
It must open (shut off the motor) just as the finger slides off the "ramp"
and into the slot.  When it closes is dependent on the motor speed for
smooth operation.

	Thanks for all your help, Derek! 

	Derek: You're welcome (but you did all the work.) 

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