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"....To boldly go where (few) have gone before ...."
I'm quite sure that you didn't catch a little tidbit that I threw at you earlier on. I said, when we were discussing the replacement of the sensors and LEDs, "with a little bit of luck, we can fix the problem with a minimum of hassle". What I failed to mention was, what was it exactly that we needed a 'little luck' for? The repair seemed to go quite well, so what was the 'luck' all about?
The 'luck' was... we were able to get the sensors completely out!! But what if we hadn't been able to? What if a part of one of them... or a part of one of the LEDs... just didn't cooperate? What would we have been faced with?? We'd have been faced with............ GOING INSIDE THE GEARBOX!!!!
And as most people have heard at one time or another, this area is only for the brave of heart! It takes a minimum of having a background in Quantum mechanics and General Relativity, as well as experience in celestial navigation and making fudge brownies, before one dare tread into this chamber of horrors!!!!
But what did I know? I wasn't aware of how hard it was to adjust that mask that falls out, so I went inside, did what I was going to do, adjusted the mask, and closed it up! Only later did I discover that it wasn't easy! After I'd already done it pretty easily!
That being the case, I thought I might show how a person can go inside the box, and if necessary, remove the mask or the disk, so as to push the remaining pieces of sensor or LED out of it's holes, then finish the repair. Then, maybe , we can bring this long winded discussion to an end!
Before you begin to open the gear box, there's a possibility that you can do something that will help a lot in the alignment. I call it 'insurance policy #1".
At the bottom of the gear box, on the outside, just below the sensors, you might see the very end of the mask, sticking out a bit. (The black tab. ) If so, use a straight pin or razor blade to scribe a line on it, right along the bottom edge of where the side frame rests. Also, scribe a mark where the two sides of the mask align with the frame. They would be a big aid in relocating the mask back to its original position.
If the edge of the mask doesn't stick out at all, that's okay. We just won't have that extra insurance policy.
This image is of the R.A. assembly. If you're working on the DEC assembly, before you begin disassembly, remove the DEC knob from from it's shaft, then either file or sandpaper the shaft smooth. You want to remove any burrs on the shaft, left by the knob holding screws.
What you're about to do is to remove the four hex screws that hold the left (as shown) end plate to the unit. When they're removed, the end plate will still be held in place by two aligning pins, so it won't just drop off into your hand.
Although it's difficult to see in this image, you may be able to make out the strip of plastic that's just to the left of the leftmost gear. It runs from the front of the opening to the rear. I mention this plastic strip, just so that as you slide the left plate off .... it has to be slid to the left until it clears the metal gear shaft... you know what's what.
All you want to do is to remove the holding screws, then slide the plate to the left until it clears the shaft. The only 'gotcha' that you should be aware of as you remove the plate, is that the shaft that passes through the plate where the bronze busing is, may want to try to slip along and come off, too. If it begins to slide, simply push it gently back into the gear housing. That was the reason for smoothing the shaft before beginning, so that the shaft doesn't catch on the bronze bushing.
The gears and the timing disk are now exposed for you to see. With a small amount of luck, the timing mask is still sticking to the plate you just removed. If so, we'll put insurance policy #2 into play. If not, we'll do fine without it.
This shows the gear train with the cover removed... and without that pesky gear on the shaft that might have given us trouble when removing the side.
In the left image, you can see the two holes at the bottom right, where the LEDs are mounted, and in the right image, they are covered by having our timing disk in place. See? No problems yet, are there?
Depending on what reason we disassembled the unit, will determine what we do next. We'll assume that what we need to do is to get some remaining plastic out of the holes from the LEDS, beneath the timing disk. That means we need to remove the timing disk to get access to the holes. No problem at all!
Removing/replacing the timing disk.
To remove the timing disk from it's mount, you heat the face of the disk with a soldering iron. After a few seconds, you use an Xacto blade or a single edged razor blade or anything similar and sharp, and begin to slide it between the disk and it's mount. Heat, then slide the blade in. Heat, then slide it again. Rotate the unit a little by gently turning one of the gears a bit, and repeat.
It may take a bit of time, so don't get impatient. Each time you 'cut' into the glue that bonds the two items, you'll make a little more progress. Heat and slide the blade in. The glue, when heated, will soften and get very sticky, so expect it.
Before long, you'll have separated the two far enough to have them completely apart.
Clean the glue off of the timing disk and the mount, with alcohol or acetone or any other substance you think will dissolve and cut through the sticky glue. Once again, it can take a few minutes to get both surfaces completely clean, but do it anyway. Get all of the old glue off.
If you took the timing disk off because you needed to get access to some remaining chips of the LEDs, you have easy access now, to their mounting holes. Clean the holes with the same kind of glue remover as before.
To mount the disk back into place, first just hold the disk back up to where it will mount. You'll see that there is a hole in the center of the disk that is the same size as the hole in the mount. That means that all you need do is to apply a good glue to both surfaces, then align them together and press them together for the time needed.
For this bond, I use 3M Super 77 spray adhesive. It gets tacky quickly, and it seems to have the consistency of the bonding agent that was removed. I'm sure that most hardwares or building supply houses will sell this adhesive or something very similar. I bought the spray can version of it, and applied it with a toothpick, rather than spray it directly on. I didn't want to take a chance of getting into any of the slots. Besides, I already had some of this stuff in spray can form from another project, so I used what I had.
See? Removing and replacing the timing disk is a snap!
Removing/replacing the timing mask
There are several ways of removing and replacing the mask. Or should I say, of replacing it, since removing it is quite easy.
If you found that when you opened the unit, the timing mask was glued into place... insurance policy #2 ... then what you want to first do is to take a sharp pin and etch the outline of the mask onto the plate that it's mounted on, before removing it. That pretty much takes care of how to align it in that situation.
If that's not the case, then how about insurance policy #1? Were you able to scribe marks on the mask while the unit was still closed? If so, then sit the mask back into place so that the marks all line up, and again scribe the outline of the mask onto the plate. Again, that solves that.
No luck with either method? Then let's cover several ways of aligning the mask, depending on circumstances and which one you prefer. From here on, we'll assume your mask just fell out of alignment before you could do any marking.
If you need to remove the light sensors for a previous repair, then do so now. With them out of the way, it makes things a bit easier.
Now, regardless of whether or not your light sensor holes are available to you or not, take a small dab of white grease, if you have some, and put a small dab on the CENTER HOLE of the timing disk! You could also use a crayon or any other thick marking material if you don't have the white grease. Just something that will leave a mark for you.
Slide the plate back on the shaft, and move it up into position, aligning pins aligned and everything. Now slide it back off again. But this time, you'll see a small smudge on it that shows where the center of the timing disk aligns with the plate.
You may not have noticed before, but the slots in the mask, just like those in the disk, are pointed right at the center of where the timing disk is. That makes sense, since all slots are meant to be aligned with each other.
When you get it off, use a scribe or sharp pin, and mark a spot right in the center of the grease glob is, or whatever it was that you used to mark the center of the timing disk.
Method #1: The light sensor holes are empty
With the light sensor holes available for us to look through. that makes things even easier.
First, sit the mask approximately into place for where it's going to be mounted. Then, take a small piece of adhesive tape and tape just one corner of the mask into place. Don't get any tape on the slots.
Next, move the mask around so that it looks as if it's pretty much covering the two holes equally and then, by just looking, set it so that it appears that all six of the slots in the mask are aiming at the scribe that's for the center of the timing disk. Push the tape a bit more firmly.
Next, look at the unit from the other side, looking through the holes for the light sensors. With only a small piece of tape holding the mask, you can still move the mask around, while looking at the slots through the holes. Get the slots so that each set of slots appears to be relatively centered on it's hole, and more importantly, that all of the slots point to the point that's the center of the disk.
In these examples, for instance, the three mask alignments at the top are more than good enough to give good pulses, even though they aren't exactly aligned in their holes. If they were, it would be even better.
The second row of masks would not work as well, because although they appear to be relatively centered in their holes, their slots don't point to the center of the timing disk.
It may be a bit hard to see the difference, but if you look at the last row, you can see that the leftmost mask points to the center, as desired, while the second one points to the left of center, and the right one points to the right of center.
Strive to make the slots point at the mask center, and also have the slots as close to the center of the mounting holes. Once you have the slots aligned in this fashion, turn the plate over and glue the mask into place. It's done!
I once again use the 3M adhesive above. I apply a small dab to the very tip of a toothpick, then gently spread it on a SMALL area of the mask and adjoining plate. After it dries some, I'll do another spot. Keep the glue from building up so that it doesn't interfere with the rotation of the timing disk.
Side point here: Once you get enough glue on to hold the pieces firmly, scribe the outline of the mask on the plate. You don't want to have to do this again if it isn't necessary.
Aligning the mask from the inside
The final alignment method you need to see, is when the holes already have the light sensors mounted, which keeps you from looking through them to see the slot alignment.
In all likelihood, you could probably just sit the mask into place, aim the slots at the center point of the disk, glue it down, and you'd be fine. The only real difference is, from the inside, you can't completely see all of the holes that you want to align the slots to. You can, however, more easily see the mark for the center of the timing disk.
I'll show you TWO different methods, both equally easy and accurate, that can be used for aligning when viewing from the inside. From there, you can probably improvise other, even better methods.
Method #1:
The first method needs no drawing for it. Simply take a thin piece of transparent plastic that's slightly larger than the mask. A piece of plastic no thicker than a sheet of paper, from an office supply store will work. Lay the plastic down on a flat surface and trace the outline of the mask onto the plastic sheet. Also trace the cutouts for where the slots are. Then, take the plastic sheet and cut out the piece that you traced, exactly. It will be the same size and shape as the actual mask.
Then, using this transparent 'mask' lay it down over the holes, center it up on the holes, and be certain that the slots are aiming at the center point for the disk. Tape it somewhat into place, and then trace the outline of the plastic mask onto the metal piece. Finally, lift the plastic sheet off and replace it with the real mask. Glue it into place and you're done. See? Easy.
Method #2:
Another method is to take the same kind of plastic sheet and cut a strip from it that is slightly narrower than the mask, but taller in height. Tall enough, in fact, that it is taller than the holes AND the pivot of the disk.
Next, lay the plastic strip down so that it covers both holes, as well as the pivot point, and tape it to the plate at the top of the plastic. Using a permanent type of 'magic marker', carefully darken the plastic over the two holes that house the photo sensors.
Slide the mask under the plastic and align the slots with the blackened spots that represent the holes. Align the slots so that they again, aim at the pivot point of the disk. Then glue the two edges of the mask. Once the two edges have dried enough, remove the plastic and glue the remaining edges.
It should be very apparent that the key to aligning the mask properly, is to simply concentrate on having the slots in the mask aim at the center point of the disk. If that condition is met, then all of the slots, both in the mask and in the disk, are automatically in alignment. All that's left for you to fine tune, is to set the mask so that the slots in the mask make maximum use of the space allowed for light, through the mounting holes.
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