Illustrated Cataract Repair

by

Doug Harland

I’ve done a number of cataract repairs on roundies and rectangulars. The most successful method used a heat gun. Others too have found it to be an effective way to remove the lens.

But, before beginning you must determine who made the CRT. Was it Zenith or RCA?

If it’s an RCA (with its characteristic mold-like cataract underneath the lens) the heat gun method is by far your best bet. If it’s a Zenith (with the green-halo symptom) the bonding material is different — much more gel-like. If the heat gun method is used on a Zenith tube, you will probably crack the lens from overheating. The electric "hot wire" technique has been successfully used to separate the lens from a Zenith CRT.

We'll discuss the heat-gun technique as applied to an RCA 21FJP22 on October 15, 2006 .

To support the CRT, I have an 18-in. diameter cardboard barrel. I put blankets around the edge of the barrel as an added cushion for the CRT.

The RCA 21FJP22 CRT.

RCA tubes will have a tape around the circumference of the lens. You must cut around it with a razor knife.

The next step is to preheat the CRT with a 500-watt halogen work light aimed directly at the face of the tube, about 6-in. away. After 10–15 minutes, the lens is nice and warm.

Preheat with a halogen work light aimed directly at the face of the tube.

Using a heat gun on the high setting, I start at the edges of the CRT and work the gun very slowly in one area at a time.

Little "fingers" of air pockets begin to form.

Once the screen lens gets hot enough, it will begin to separate from the PVA material. You will see little "fingers" of air pockets begin to form.

Move the heat around.

Continue to move the heat around until these air pocket fingers merge.

You might want to insert a wood wedge (very thin) into the edge to create a slight upward pressure on the lens. It will help the air pockets break open, which helps to separate the lens from the CRT. You must be extremely careful when putting the wedge in, just a very slight amount of pressure is needed. Do not attempt to use the wedge as a tool to lift off the entire lens, or you might break the lens.

As you heat more and more of the lens, use your fingers to gently pull up on the lens, so you can judge how much more heat is required to separate the lens.

You will notice that the air pocket fingers will begin to dissipate as you move away from an area you are heating. Periodically, go back over an area you already heated to reform those air pockets.

Gently pull the lens off the CRT.

Once you get the lens hot enough, you should be able to gently pull the lens off the CRT with the PVA material remaining only the face of the CRT. If the PVA comes off the lens in strands that look like the air pocket fingers, you didn’t get the lens hot enough.

 It’s difficult and time consuming to remove pieces of PVA stuck to the concave lens.

Now, assuming the PVA is only on the CRT face, quickly grab the edges of the PVA and pull up on it slightly. As it’s still hot, it should simply peel off the face very smoothly and easily.

Grab the edges of the PVA and pull up.

Of course there will be small bits and pieces here and there that won’t come off.

Use a razor blade to scrape off small bits from the lens and/or the CRT. Use gasoline on a rag to help dissolve any remaining film that’s left on the CRT. You will get it nearly perfect.

Scrape off small bits from the lens and/or the CRT.

After that, use Windex or some other glass cleaner with newspaper as the rag to clean the rest of the glass. This will insure a clean, streak-free surface.

Clean the rest of the glass.

As for remounting the lens, the best way is to use double sided foam tape (by 3M) and put a few 1-in. long pieces around the circumference of the CRT, being careful not to place the tape too far in, or you could see it when you remount the CRT  to the bezel.

Foam tape as a spacer/cushion.

You must use the foam tape as a spacer/cushion. If you do not do this, the center of the lens will touch the center of the CRT, leaving about a 1/16-in. gap on the edges. If this is left unattended, remounting of the CRT will compress the lens creating undue stress to the glass.

Some have questioned whether the PVA or lens spacing affects picture quality and/or focus. The answer is no, not at all. The PVA is clear and will not affect the appearance of the tube or the picture.

After centering the lens on the CRT, seal the circumference of the tube using clear packaging tape.

Seal the circumference of the tube using clear packaging tape.

Clear tape prevents dust and debris from entering the space between the lens and CRT.

The CRT is now ready for the cabinet.

You might need to adjust the CRT mounting hardware to compensate for the fact that the distance from the edge of the CRT lens contact point to the mounting bracket might have changed. This is because the original PVA material set the "gap." The foam is slightly thinner than the original thickness of the PVA at the edges of the CRT.

Once reinstalled, the picture will be perfect as new and look great. You'll never have to worry about cataracts again.