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Discussion Starter · #1 · (Edited)
Disclaimer and Warning. I have performed this process only once. Although it dramatically improved contrast and deepened black level on a poor performing, used X790, I do not have appropriate test equipment to accurately measure contrast ratio. However, I do come from a CRT projection background and have a slight inkling of what a contrast improvement looks like. This is presented to the forum to document my adventure. I do not recommend this process for the average projector owner. There is considerable risk to projector and person doing the work. Doing this on your own machine is totally at your own discretion and risk.

I had recently "black/mirroring" of a DIY lamp iris in an RS45 with fantastic visual results. A used DILA-X790 arrived and I had expected it to blow away my modified RS45, but try as I may, the stock configuration of X790 simply produced a milky, flat image compared to the RS45. Indeed it was brighter, but even when with closed down iris to match the RS45's light output, the X790 could not create the clarity and image depth I got with my "black/mirrored" RS45. How could a modified ancient machine look so much better than a vaunted, later model with much higher rated contrast ratio?

I thought perhaps the light block was dirty. No, internal inspection showed the light block to be in good condition. New lamp was tried. Performed multiple gamma calibrations with various gamma's and still, the picture was not beating my ancient, but modified RS45. Because the RS45 had its largest leap in image clarity and black level after I black/mirrored its DIY iris, I decided to do that to the JVC OEM lamp iris.

What is black/mirroring? Basically making the side of the lamp iris facing the LCOS panels black and the lamp side of the iris mirror polished.

Why? LCOS rejected light is reflected backwards towards the lamp. Along the way, it can scatter. Blacking the iris absorbs that rejected light. Some of that wasted light may get recycled with a shiny iris surface, but the cost is reflection back forward of rejected light. On the lamp side, I polish the iris to mirror finish to recycle otherwise wasted light and reduce heating of the iris.

This thread documents how I did it. When I was done, the results were stunning. Black was deeper, light output was slightly reduced by about 10%, but wow the picture gained depth. I spent hours looking at material that looked mediocre on the X790. It was obvious. Blacks were darker, but bright scenes were still able to hurt my eyes. My wife, who was unimpressed with the switch from RS45 to X790, proclaimed she was much happier with the picture.

THX eclipse finally had a background darker than the RS45's rendering. It looks a lot like auto iris, but WITHOUT auto iris. LG's OLED demo video looks fantastic now.

I am awaiting arrival of a better light meter to take objective measurements. To these experienced eyes, this changed a disappointing X790 into a smile inducing machine.
 

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Discussion Starter · #2 ·
First order of business was to prepare the X790 for disassembly. Lens cover was set to remain OPEN. The reason for this is we actually need to free the entire light block to access the OEM lamp iris.

For those who have never opened their machine, here were my (not necessarily best or complete) steps

Remove the side covers by inverting the projector to access projector bottom.
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Six screws must be taken out.

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Then the side covers tilt out and can be removed.
 

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Discussion Starter · #4 ·
Top metal cover is secured by multiple screws (green).
Also, you must free the rear corner from its shield tape (yellow).
Note that two screws (red) that secure the projector front are different from the others.
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The cover then slides backwards and lifts up to remove.
 

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Discussion Starter · #5 ·
When one adds a DIY iris, the next step is to remove an air exhaust cover at the rearward portion of light block. I removed the exhaust cover to gain easier access to the two iris mounting screws. This may not be strictly necessary for removing the OEM lamp iris. I did it because I was planning to slide the OEM iris out much as one would insert or remove a DIY iris.

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A single screw holds the air exhaust cover. A right angle driver is ideal.
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Under the air exhaust cover is a mounting spring for a square polarizer combiner. The spring clip will usually dislodge or fall off when the exhaust cover is removed.

WARNING: Without the spring clip securing the polarizer combiner (hereafter PC), that fragile optical piece can slide out if you tip the projector!!!! Either never tip the projector or safely remove the PC before it falls and gets damaged. Do NOT touch with your hands or oils will transfer and be near impossible remove. Use gloves and/or pickups. Also, note orientation of the PC. It must have its channels vertical.

Here is the PC in red. Also in yellow are metal tabs you must take caution to never touch lest you dislodge or break a color mirror.
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Discussion Starter · #6 ·
Here is the OEM lamp iris which we want to remove.
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Oh no! Unlike a DIY iris, the OEM iris is simply too deep to simply slide out. When it hits slide out limit, there is still another 10 mm more clearance needed.

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So much for the simple plan. Instead, I had to free the entire light block. Lift the light block enough to get clearance to take out the iris. Way more work than originally intended.
 

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Discussion Starter · #7 ·
The light block is actually only held in place by three screws, but MULTIPLE cables and items must be disconnected or removed to actually free the light block.

First the front projector cover must be removed. Here is where I learned to warn about the PC falling out. Luckily mine only slipped a little when I tipped the projector. I usually put the projector on its side to access the two screws of the front cover. Either tip the other direction instead of what I show in this picture or better yet, leave the air exhaust in place.

Two screws hold the top cover to projector bottom.
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You must also detach three cables.
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Note the rubber hood (green arrow) that goes around the lens. You must gently stretch it back over the lens when you later put the front cover back on.
 

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Discussion Starter · #8 ·
Detach the iris cooling fan cable.
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Just a couple screws hold the iris cooling fan down. Once those are removed, the entire iris cooling fan/duct lifts up and out.
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Discussion Starter · #9 · (Edited)
Next, the DILA cooling fan must be removed. Don't detach the ductwork that is connected to the light block. You only want to remove the cooling fan and its portion of ducting.

Detach the iris cooling fan cable. I actually pulled the fan before the cable, but I suggest detaching the cable first.
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Also, you may benefit from detaching the temperature sensing cable (yellow) that stretches over the DILA cooling fan.
Two screws (green) towards rear of DILA cooling fan

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Two screws at front of DILA cooling fan.
Also free up the cables routed through the slot (yellow)
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Cooing fan then pulls forward and out front of projector.
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Slides out forward once screws and wires are freed.
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Here is what it looks like with the DILA cooling fan out. The portion of ducting connected to light block remains in place.

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Discussion Starter · #10 ·
DIsconnect the iris cable connections.
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Remove rear duct cover (green arrow) to gain access to the lamp power cable connectors. This pict is from an RS45, but the rear duct cover is same. It is held in place by a couple screws and shield tape.
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Discussion Starter · #11 · (Edited)
Disconnect lamp thermal switch cables (red/black in clear plastic) to gain slack. Be mindful of polarity when reattaching later!!!!
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Examine all cabling and free any that lack slack. It is a good idea to free all from their bundling clamps albeit not necessarily disconnect from connectors.
 

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Discussion Starter · #12 ·
Light block is now ready to be freed. Three screws hold it in place. Next to each screw you will also notice plastic alignment peg. Remember that for when putting this back together.

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It's only three screws.

No need to remove this other screw.
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You can now gently lift the rear of light block up enough to remove the iris. Be ever vigilant about cables getting stretched!

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Discussion Starter · #13 ·
Here is the OEM iris in its full glory.

The lamp facing side.
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The LCOS facing side has the tabs.
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The "petals" slide along tiered pegs. Each petal has linear teeth that engage drive gear.
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Discussion Starter · #14 ·
Four screws (green) hold the cover plate. Two screws hold the motor assembly.
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Motor removed
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Black gear removed.
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All gears removed.
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Back plate removed
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Discussion Starter · #15 ·
Iris completely taken apart.
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Tabbed plate degreased and masked for painting
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Lamp side of each petal was polished with cutting and polishing compound to achieve a better mirror finish than what JVC does. The one on the left has already been extra polished. The one on right is stock polish level. Notice the clarity of reflection on the extra polished surface. This should improve light recycling efficiency.
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The lamp side of the petals was scuffed with 800 grit scuffing pad to give paint a better bite surface.
Note that only the optical portions of each petal were polished or scuffed. The hidden mechanical slide portions were not modified.
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Discussion Starter · #16 ·
Masked for painting
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Paint was Rustoleum FLAT, high temperature barbecue paint.
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One hour of drying
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Held in pliers, each piece was heat treated 15 minutes each piece with 1500 watt heat gun on high and held four inches away from paint while making circular motions.
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Discussion Starter · #17 ·
When reassembling, be mindful of putting each petal in its own tier
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Close both petals equally so they will be in proper sync with each other when gear is later inserted.
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Add back plate
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Add gears
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Test iris motion by manually turing the black gear. Once verified OK, add the motor.
Ready to install...
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Reassembly is reverse process. Just be very careful to get all connector and cable routing correct. Don't forget to stretch the rubber cowling over lens as you attach front cover.

That's basically it for the process. Upon projector startup, run the iris up and down the entire range to get lens and lamp irises synchronized.
 

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The aperture is much smaller on the 790. It looks more like the one I made for my 4910, 18mm. How big is it and does it stay in the 16:9 configuration or does it reduce to a square? Excellent work, and fast. Do you sleep?😁
 

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Discussion Starter · #19 ·
While I had the project apart, I actually also pulled a couple other fans and cleaned them with compressed air and brush. Look out for the little rubber mounting pegs on each corner of the fans. I lost one for about 30 minutes because I didn't take one off before blasting with air.

Projector is working fantastically except for a noisy iris cooling fan that I need to replace.

After black/mirroring, the X790 is finally throwing a picture I am happy to watch. In OEM state (albeit a used machine), I would never have been happy.
 

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Discussion Starter · #20 ·
It opens to a cross shape. I'll post some dimensions later today.
Nope. Have not slept all night. I'm that excited about this mod and its effect.
Running out of steam now.
 
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