CrystalEYES repair

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Introduction

Starting October 1 2009 RealD stopped accepting out of warranty CrystalEYES glasses for repair. Previously they had been repairing them for a bit more than $100 per pair, no matter what was wrong with them. However now the only supported option is to replace them. This is a very expensive option. Since we had a fair number of these around in various states of disrepair I decided to see how hard it would be to fix them. Some of these had shutter defects (black blobs), others had broken battery compartment springs, and a few others had what appeared to be electronic issues, with, for instance, one shutter not working, or goggles only working for a brief time. If one working pair could be made from two broken ones, that would be much cheaper than buying one new working pair. Also a box of unused, and mostly broken, CE2 and CE3 had recently been obtained from Doug Rees's lab, so there was a lot of material to work with. (That lab now uses NuVision equipment, and the NuVision emitters are not compatible with the CrystalEYES goggles.) Fixing the battery compartment does not require disassembling the goggles, but all other repairs do. So taking the beasts apart without destroying them was the first order of business. Luckily one of the pairs from Prof. Rees's lab had a badly broken case, which let me poke around inside to see what held it together. All of the goggles available are marked as being made by Stereographics, so if RealD has changed the design of the CE3 since acquiring Stereographics those changes will not be indicated in these notes.

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Disassembly

In order to avoid the ironic fate of losing an eye while attempting these repairs, one should wear safety glasses during the disassembly of the CrystalEYES goggles.

Exploded view of disassembled goggles

disassembled CrystalEYES goggles

Above is a picture of a disassembled pair of CrystalEYES. The outer frame (A) holds the shutters (B) and the circuitry (D), which is then held in place by the inner frame (C). Mechanical junctions are of three types: hook and groove, tongue and groove, and post in a hole. There are three hooks around each eye in the inner frame, indicated by the red arrows in (C), which fit into corresponding grooves in the outer frame, one of which is highlighed (red arrow, A). These are nominally reversible fasteners, however the hook may break off, and there may have been glue applied to the grooves. More on that below. There is a tongue (green arrow, A) and groove (green arrow, C) on each side which help align the two halves of the case. Finally, there is on the outer side of each eye a post on the inner frame (blue arrow, C, here drilled out) which is inserted into a hole in the outer frame (blue arrow, A). This post is always glued in place and must be drilled out or snapped off in order to open the case. Note also the 4 dots on the outside of each shutter gasket. These act in pairs to conduct the control signal to the actual shutter which is retained by a surrounding rubber gasket. These dots have a DC resistance above the range of a common multimeter (in excess of 4 MOhm), but presumably pass the AC drive signal to the shutter.

shutter schematic

The Right and Left shutters are not interchangeable. Above is a schematic of the layers in each shutter as seen from the top or bottom edge. Blue is polarizer, red is glass, grey is the liquid crystal, and green is the conducting pad, which is located under the 4 dots in the rubber shutter gasket. Not shown: internal conductors and edge seal. If a left shutter was flipped over and placed in the right portion of the gasket, the conducting dots would be in contact with the glass, and not the conducting pad, so it would not function electrically.

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Details of partially disassembled goggles

left temple view right temple view outer frame with circuit and shutters

The preceding three pictures show how the outer frame, circuitry, and shutters fit together. The inner frame has been removed in this picture, but all the other components are in their normal positions. Note the microswitch in the lower right corner of the right temple circuitry, this is activated by the mechanical linkage built into the internal frame (see below). Note also how the split conductors on each side rest on the four conducting cylinders which protrude through the rubber LCD shutter gasket. It appears that each half of the conductor contacts two of those conductors. However inside the rubber frame each pair of conductors sits on a single large conducting pad (not shown). Probably this provides a bit of wiggle room in the assembly and aging of the device, as one of the cylinders would be sufficient to complete the circuit. The nose piece is part of the shuter gasket.

switch linakge

The temple switch mechanism in the inner frame. Viewed left to right, are the external button (which is pressed automatically when the glasses open and extends inward and downward in an L shape), the internal frame, and a compound spring, consisting of a long thin platic piece extending nearly the full height interior frame which is backed by a copper spring. The L shaped piece of plastic starts at the external button, passes through the inner frame, then passes over the plastic/copper spring, and then extends down to press the microswitch. The long part of this L shaped piece extends down in the picture vertically from the shiniest part of the copper, which is an extension of the copper spring.

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Drilling instructions

Drilling Measurements

In order to open the case the pole on each side must be broken off (not recommended!) or drilled out. Removing the base of the post is most easily accomplished using a drill press with a 9/64 inch bit. The post itself is very close to 7/64 inches in diamater, but it is hard to drill that precisely on these goggles, and the slightly larger bit increases the odds that the entire base of the post will be removed on the first attempt. Shown above are two equivalent sets of measurements for marking the center of the hole to drill in the inner frame. The right side is shown, but the numbers apply as well on the left side, of course in the mirror orientation.

drilling orientation

The pole is aligned parallel to the flat top and bottom of the goggles. To drill it out accurately the goggles must be propped up as shown. In this orientation the pole is vertical, however the surface of the innter frame at the drilling point is not horizontal. The center of the drill bit should pass through the center of the marked point on the inner frame, even though the bit will not be perpendicular to the surface. The paper pad shown in the picture, which is used as a wedge, is about 1mm thick on the thin edge and 7 mm at the thickest point. However, even with the goggles propped up it is difficult to keep the frame in position as the drilling proceeds because the frame bends under the pressure of the bit. For truly reproducible drilling one would need to construct some sort of cradle to hold the goggles in exactly the right position. The thickness of the inner frame is about 1.5 mm, drill the hole so that its outer diameter is that deep, and a touch more, then inspect the hole. If the hole was placed perfectly, and the frames oriented properly, there will be nice round circle where the remainder of the post can be seen embedded in the support from the outer frame. This is really obvious in a CE2 model because the support is white and the post is black. If the drill was a little off just move the bit over a smidge and drill off the rest of the base.

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Releasing the hooks

normal hooks glue damaged hooks

Before proceeding to pry the goggles open after drilling, a note about glue. In the pictures above are shown on the left the hooks from a very old pair of CrystalEYES which were not glued, and on the right the same hooks, from a different angle, of a more recent pair which were glued. It appears that the frames are glued together at the poles and every pair of hook accepting grooves, and moreover, that the glue is placed on the outer frame before final assembly, then the inner frame is snapped into place. When disassembling a glued frame even after drilling out the post something has to break: the glue, the hook, or the frame around the groove. The picture at right is pretty typical, where the outer layer of plastic on the inner frame tore off and stayed in the groove. This is about the best you can expect, since the glue seems to be stronger than the hook plastic.

Once the posts have been drilled out it is time to remove the inner frame. If the frame has not been glued then you will be able to spread the top and bottom of the outer frame by hand, by grasping it top and bottom at the center of one eyepiece, fingers only on the outer frame. If it doesn't budge then the frame has been glued. For a nonglued frame a little gentle prying with a flat bladed screwdriver near the hooks is usally all that is needed. For a glued frame substantial force with the same implement will be required.

To take apart a glued frame "gently" pry the inner and outer frames apart starting near the upper part temple region. The goal is to detach the top hook from its groove on each side. Be careful not to pry against the circuit board which runs along the top inside of the outer frame. Once both of those hooks have been freed let the right side snap shut. Pry open the left side about 4 mm near the top hook and wedge something soft in the crack to hold it open. The purpose of this wedge is to provide a little more room for the inner frame to move while the bottom is being pried. Then insert the flat blade of the screw driver between the inner and outer frames directly between the hooks at the bottom of the eyepiece. This can be very hard to do and it will mar the surface slightly. Once the blade is in slowly advance it towards the inner hook and pry the inner frame up from the outer frame. That is, displace it in a plane parallel to the shutter. The idea is to break off a little bit of the hook as in the photo above, but not the hook itself. Both success and failure are indicated by a medium loud crack and a sudden displacement of the inner frame away from the outer frame. Repeat this process on the outer lower hook.

At this point both poles and the 3 left hooks plus top right hook are detached. Snap the frame back together fully, pry open the top right hook (already released), wedge it, and repeat the same procedure used before on the left side on the right bottom to release the final two hooks. Do it this way because attempting to twist the inner frame out from the free left side will tend to break off one or both of the hooks on the right side.

Once all of the hooks have been released on the right side, re-release those on the left side, and slide the inner frame out of the outer frame. The circuit board and shutter assembly are only held in place by friction and can be removed without tools once the frames are appart.

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Shutter Optics

The shutters utilize crossed front and rear polarizers and the liquid crystal acts as a half wave plate. This can easily be demonstrated. Starting with two shutters from one disassembled goggle (or use one shutter from each of two pairs of goggles) rotate one shutter (far) until the LCD monitor viewed through it is black. Then place the other shutter (near) between the far shutter and the monitor, and without moving the far shutter, rotate the near one. When the near is 90 degrees rotated with respect to the far it will be possible to see the monitor brightly through the far shutter by looking through the near shutter. That is, the near shutter will appear like a shutter shaped bright window into the monitor, surrounded by all the rest of the monitor, which will be dark. What happens is the polarized light from the LCD display (assume here it is vertical) enters the near LCD through its front polarizer, which is now vertical. This light is then rotated 90 degrees by the liquid crystal and exits through the near shutter's rear polarizer, after which it can enter the far shutter's front polarizer, which is horizontal (which is why the LCD monitor was originally black when viewed through it), rotates another 90 degrees by the second liquid crystal layer, and exits as vertically polarized light once again from the rear of the far shutter. Of course you can also see the monitor clearly by just looking through the near shutter, without also looking through the far one, but that view does not reveal anything about the polarization of the light coming out of the shutter.

If a bit of polarizer is available the rotation of the light through the shutter is also demonstrated easily as shown in the following pictures.

normal view sideways view

The polarized light from the LCD monitor (red) either passes through the aligned polarizer (red) or is blocked by the crossed polarizer (green). For the shutter the orientation of the front polarizer is indicated.

shutter as half wave plate to block shutter as half wave plate to pass

Components are in the order: LCD monitor, shutter, then polarizer. The polarized light from the LCD monitor (red) passes through the front polarizer of the shutter, is rotated by 90 degrees (blue), and exits through the rear polarizer. The light is then either blocked (left) or passed (right) by the final polarizer. The inactive shutter is a very good broad spectrum half wave plate.

cellophane to block cellophane to pass

For comparison the same test is shown using a sheet of cellophane instead of a shutter. Cellophane is strongly birefringent and is sometimes manufactured in such a way that it is close to a half wave plate. (The cellophane was kindly provided by Dr. Keigo Iizuka of the University of Toronto.) This particular piece of cellophane has a wavelength dependency which is revealed in the blocking test on the left, where the red light comes to closest to being rotated perpendicular to the final polarizer and fully blocked. The amount of rotation achieved for the other colors differs slightly so that some of those colors pass through the "crossed" polarizer in the left image. Note that the angle of the cellophane was adjusted to achieve the maximum amount of blocking possible for the image on the left. The angle of the cellophane was much less critical when it was used to rotate light towards an aligned polarizer as in the right image. The difference in alignment sensitivity is likely related to the eye's ability to perceive the difference between 100% and 80% intensity versus 0% and 20% intensity. The small change in intensity in the bright light is not too apparent, but the change between nothing and something is quite easy to see.

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Circuit Diagram

(Not available.) Defective electronic components are going to be difficult to repair. The discrete components could in theory be replaced, but special tools will be needed as they are surface mounted. In addition to the resistors, diodes, and one crystal, there is one large IC, probably custom, and a few smaller ones which seem to be commodity parts. On a very old pair of goggles these included an LM385 M1.2 (a 1.2V fixed reference voltage in an SO package), a Motorola MC14575D (quad programmable operational amplifier), and a Texas Instruments TLC2LAI (also marked with "4CT A987", a dual operational amplifier).

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Reassembly

Insert the rubber gasket bearing the shutters into the exterior frame. Be sure it is neatly tucked in between all of the surrounding retaining posts. When viewed from the front there should be no gaps between the external frame and the rubber gasket. Insert the electronics into the exterior frame, aligning the conducting loops over the posts on each side of the shutter gasket. Press the electronics in far enough to expose the top two grooves in the external frame. Snap the inner frame into the outer frame. Cover the post holes with a bit of tape to keep dirt out of the inside of the repaired goggles. Because the posts on each side are not restored the inner and outer frames should be reinforced by taping them together at two points on each side. The tape was applied just anterior to the temple hinge on the bottom of the frame, and about 2cm anterior of the hinge on the top of the frame. In both locations a piece of tape about 7 mm X 20 mm was employed (the size of the tape is not critical). Glass reinforced strapping tape would probably be a little better mechanically, but it didn't seem like a good idea to put a material that sheds glass fibers that close to the eyes. I used McMaster-Carr part number 7631AY1, which is a .007 inch thick aluminum foil tape with an acrylic adhesive. (That part has apparently been discontinued, but 7631A41 is a similar, albeit slightly thinner, tape.)

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Repairs

Battery Case

battery spring fix

In older battery cases there is a slot on each side into which the arms of the battery spring recede when a battery is in place. The spring is retained by a post of plastic from the battery case which passes through its center, and has been melted into a blob. The design puts a fair amount of stress on the thin center post and the blob tends to snap off, at which point the spring falls out. In the picture above this spring is shown at the right. To restore battery case function a simple flat conductor may be used in place of the missing spring. Aluminum foil works, but since the batteries are stainless steel, and the environment near the head may be humid, corrosion could occur. For this reason .001" steel was used. It is available as "shim steel" from a variety of sources. The piece shown here was cut from a 6" x 9" sheet, part number 1010-1 from Small Parts Inc, P.O. Box 4650 Miami Lakes, FL 33013-0650. This material is much stiffer than even heavy duty aluminum foil, and can still be cut with a scissors, although not with a razor blade. The conductor in the distal compartment, where the positive electrode makes contact, is filled roughly to the edges, since there is no possibility of the conductor shorting out the battery. The conductor in the proximal compartment, where the smaller negative electrode contacts the conductor, is trimmed to be slightly smaller than this electrode. There is a very small gap between the electrodes on this side of the battery, so the safest way to avoid shorting the electrodes is to make the conductor fit entirely within the smaller electrode. It is difficult to tell from the picture, but the horizontal piece of the replacement conductor is quite flat, and does not approach the postitive electrode as it exits that compartment. A small piece of Scotch tape was rolled into a tube, cut into 4 pieces, and 2 each were used to affix the conductor in place on each side. The tape also acts as a weak spring to pres the conductor against the batteries, and the batteries against their target pads on the circuit board inside the case. The conductor is trimmed to be snug in the distal compartment and along its base, so it is not free to move about within the battery case even if the adhesive fails on the tape.

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Shutter Exchange

Disassemble the donor and recipient goggles as described above. Remove a shutter from its rubber gasket by holding the shutter gently with your fingers in the center, and pulling the shutter out of the gasket at "bridge of the nose" section, then work the shutter out of the gasket around the other edges. Install a shutter into a gasket in reverse order. Reassemble. Clean the finger prints off the shutter with lens paper.

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Black Blob Removal

shutter defect log mag shutter defect high mag

Above are low and high magnification images of the dreaded black blobs which sometimes develop in the LCD shutters. I assume that the shutters in the CE2 and CE3 use twisted nematic liquid crystals, which suggests that whatever these are, they are not liquid crystal in the appropriate state, resulting in the loss of polarization rotation, and no light transmission due to the crossed polarizers. These also reflect light in a manner which is shiny and smooth, as if all the light is being reflected from the interface between the blob and the nearest piece of glass. In some instances the reflected light is a dark blue, and in others it is a gold color. The entire blob is the same color in reflected light, and both sides of one blob are always the same color. The difference in reflected light color from blob to blob possibly indicates some variation in construction of the LCD shutters. The blobs do not move noticeably when the shutter is squeezed gently near them, suggesting that they are not gas bubbles, which would probably compress under this treatment. The black blob structures are comprised of a large number of small "blobules", all about the same size, and all of which are connected. To me, these look like some sort of 2D crystal growth.

Technical support at Boulder Nonlinear Systems Inc. kindly sent a protocol which they said might repair this sort of defect. BNS does not make the shutters in the CE2 or CE3, their instructions were for their own devices, which may (or may not) be of a similar construction. In their protocol the shutter is placed on a lab hotplate and its temperature raised above the "clearing point" while simultaneously applying a 2 Hz square wave drive signal. When this was done the shutter cleared at about 62°C, but leaving it there for an hour had no effect on the blob. Note that, ironically, at the "clearing point" these shutters turn black (lose their transparency). Presumably this is because they stop working as a half wave plate and the front and back crossed polarizers block all transmitted light.

Since the initial conditions were not enough to remove the blob, the temperature was raised slowly until it was a little above 90°C. At that point when viewed in reflected light the blob could be seen to be shrinking a bit, and a sort of ring was visible around it, possibly indicating melted material diffusing away from the blob. The shutter was maintained at this temperature for about 90 minutes. At that point the blob had shrunk by about 50% (estimate). Unfortunately the polarizer on both sides began to delaminate off of the glass. The shutter was still functional after this abuse, albeit with less clarity in the regions where the polarizer began to fail. Several weeks later the blob had not regrown, suggesting that whatever material went into solution (or another state), stayed there. Overall the experiment wasn't a great success, but it suggests that there may be a temperature window, perhaps around 85°C, where the blob will slowly dissolve without destroying the polarizer. This remains to be tested. Otherwise, a very long period, likely at least 8 hours, above 90°C may dissolve the blob, at the cost of having to replace the polarizers on the shutter. Replacement polarizer is readily available, although it remains to be seen how easy it is to remove the previous polarizer without breaking the seal between the glass plates or scratching the glass surface. Interestingly, the polarizer on the market is rated for 750 hours at 60°C, so it is no surprise that the polarizer started to fail above 90°C.

The use of a bench hot plate was not optimal. This type of heater tends to fluctuate in temperature, so it was necessary to monitor it continuously by means of a thermometer pressed to its surface. A small temperature controlled chamber, ideally with some windows, would be better suited for these treatments.

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Only one working shutter

(Not written yet.) Presumably if the problem is defective electronics it could be resolved by exchange if spare electronics are available from another set of goggles. Obviously not a solution if a spare pair are not available.

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Acknowledgements

At Caltech I would like to thank: Mike Walsh and Tim Heitzman in the Biology electronics shop for letting me use their drill press; Mike Roy in the Chemistry machine shop for donating the metal shim stock for the battery case repair; Jens Kaiser and Doug Rees for donating their surplus CE2 and CE3 glasses; Barbara Fortini for the use of her benchspace, thermometer, and hot plate; and Gary Belford in the Biological imaging center for taking the close up picture of the "black blob". I would also like to thank Michael Taylor at Boulder Nonlinear Systems for sending the thermal cycling procedure.

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Last modified 11-NOV-2009. Please send corrections to David Mathog, mathog aT caltech dOt edu.