[drh4683]

Ive done a few catercat repairs, the most successful method involved using a heat gun. I suggested the use of the heat gun after experiementation and others have found it to be an effective way to remove the lens too.

The major factor is, who makes the CRT? Zenith or RCA? If its an RCA (type of cateracts that looks like mold inside the lens) the heatgun method is by far your best bet. If its a zenith (green halo symptom) the bonding material is different, much more gel like. If the heat gun method is used on a zenith green halo tube, you will probably crack the lens from overheating. The "electric hot wire" technique is your best bet there.

Assuming its an RCA, and by far the worst of all cateracts happens on RCA type tubes, I'll discuss the heatgun technique.

As for supporting the CRT, I have a Cardboard barrel thats 18" in diameter and supports the tube very well. I put blankets around the edge of the barrel as added cusion to the CRT.
RCA tubes will have a tape around the circumference of the lens, you will need to cut around that with a razor knife.
The next step I use, is to preheat the CRT with a 500 watt halogen work light, aimed directly at the face of the tube about 6" away. After about 30 minutes or so, the lens is hot to the touch, thats what you want. Using a heatgun on the high setting, I start at the edges of the CRT and move the gun very slowly in one area at a time. Once the screen lens gets hot enough, it will begin to seperate from the PVA material. You will see little "fingers" of air pockets begin to form. Continue to move the heat around untill these air pocket fingers merge together. You might want to insert a wood wedge (very thin) into this area on the edge as a slight upward pressure on the lens will assist in the airpocket breaking open, thus seperating the lens from the crt. You must be extremely careful when putting the wedge in, just a very 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 get a feel as to how much more heat it will take to separate it.
You will notice that the air pocket fingers will begin to dissipate as you move away from a particular area you were just heating. Try to keep that pocket in there. Periodically, you will need to go back over the area you just heated to reform those air pockets.

Once you get the lens hot enough, you should be able to gently pull lens off of the CRT, with the the PVA material ONLY ON THE FACE OF THE CRT. If the PVA comes off in strands that look like the air pocket fingers, you didnt get the lens hot enough before you removed it. Its very difficult and time consuming to remove the peices of stuck PVA to the crt lens as its concave.

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

Of course there will be small bits and pieces here and there that wont come off. Use a razor blade and scrape it off the lens and or CRT. Once you get it scraped off thin enough, use gasoline on a rag to help dissolve the remaining film thats left on the crt. You will get it near perfect. 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.

As for remonting the lens, the best way is to use double sided foam tape (by 3M) and put a few 1" long pieces around the circumference of the crt, being carefull not to place the tape too far in or you could see it when you remount the crt to the bezel. 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" 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 wheter the PVA or lens spacing effect picture quality and or focus. the answer is NO, not at all. The PVA is clear and will not effect the appearance of the tube either.

After centering the lens on the CRT, seal the circumference of the tube using clear packaging tape. This will prevent dust and debris from entering the space between the lens and CRT. Remount the CRT exactly as it came out of 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 orignal PVA material set the "gap". The foam is slightly thiner than the original thickness of the PVA at the edges of the CRT.

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

Here are some pictures of a 1965 RCA roundie that I did cateract repair on.