Back in the good old days, people got their information by staring into particle accelerators that could implode at any moment, and we liked it that way, by gum! To protect against disaster, CRT monitors were equipped with a safety screen laminated to the front of the tube. Decades of use often resulted in degradation of the glue used to hold the safety glass on, leading to the dread disease of “CRT cataracts.”
Luckily for aficionados of vintage terminals, [John Sutley] has come up with a cure for CRT cataracts. The video below shows the straightforward but still somewhat fussy process from start to finish. You’ll want to follow [John]’s advice on discharging the high-voltage flyback section of any stored charge; we speak from painful experience on this. With the CRT removed from the case, removing the safety screen is as simple as melting the glue with a hot air gun and applying gentle leverage with a putty knife. We’d think a plastic tool would be less likely to scratch the glass, but [John] managed to get them apart without incident. Acetone and elbow grease cleaned off the old glue, and the restored CRT looks great when reassembled.
With its cataracts cured, [John] says his next step is to restore the wonky keyboard on his Lear Siegler ADM-3A terminal. Perhaps he should look over this VT220 keyboard repair for ideas.
Can’t say I’ve used one til that point, but some came with coatings that didn’t last.
Near as I can tell this does not restore the protection provide by the exterior lamination. Though I don’t expect a naked screen to to break into pieces in an implosion, because it’s the strongest part of the CRT envelope. No doubt the purpose of the safety glass is prevent anything striking the screen causing an implosion.
I never heard of this. All the CRTs I saw in the US have anti-implosion straps that put the face of the tube in compression, which makes it very hard to break (all stress, no strain). In fact, an implosion of a tube with a strap starts in the rear and leaves the phosphor on the screen splattered and gouged. Maybe this safety glass was a sales gimmick or required in some countries?
Interesting. I always thought the only function of the steel straps on TV’s was to hold the 4 mounting brackets at the corners. The only thing I did with CRT’s was filling them with air by cracking the thin glass tube at the back, then place in the disposal bin and hit it a few times with a large hammer… My interest was in the PCB’s and the components on it :-)
That’s an anti-glare and contrast enhancement filter. if made of lead glass, it will also reduce x-ray emissions. This 12-inch tube (with white phosphor) was used in lots of portable TV sets without any additional implosion protection.
This is an interesting video.
Regarding the implosion of CRT tubes, I always believed it to be a “problem” of mainly the older CRT’s (from before the 80’s). The protective screen was mainly to be used for situations where the user was to be expected to be close to the screen. Like for instance a terminal monitor or a large arcade screen. I also believed that such a protective screen was to act like a shield from the CRT to the user (protecting the screen from the user, who might damage it by accident OR on in case of arcades…on purpose). In the latter, a much simpler sheet of thick glass could be used, as the distance between user and screen allows for that.
Can someone confirm this or has more information about it?
The front glass on medium sized carts is usually a good 3/8 to 1/2″ think. Takes a lot to break them. I know. I have tried!
Betting these screens are more for protecting the glass from someone scratching it more than protecting from an implosion.
CRTs, not carts. Autocorrect…
The last (computer) CRT’s had a 21-inch flat surface, which had even thicker glass than the slightly curved screens.
The CRT is not laminated to the screen anymore, thus forming a gap – doesn´t that mean that one has to expect a huge buildup of dust between those layers due to static electricity? You won´t be able to wipe that dust away… but it will arguably still look better than thore cataracts.
Has he mention, in conclusion, one should put a tape all aroud to block any dust getting between the two.
I seen this type of repair done on vintage TVs I wonder of the LOCA glue used in cell phone repair could be used to glue the front glass back on with no gap?
As a former CRT technician, I would recommend using silicone caulk to reattach the screen. Put some small bearings or better yet, lead shot between the two around the edges to get even spacing and caulk the whole perimeter except for about 1/4 inch gap in one corner. After it has cured, fill the space between the CRT and the screen with a glycol solution applied with a turkey baster syringe. leave a small air bubble to allow for thermal expansion and contraction. Then seal the 1/4 inch gap. This will prevent dust ingress and preserve contrast by eliminating reflections from the inner surfaces of the glass.
Are you a sorceror?
forgive me for not getting the joke, but I rarely do, so: CRT tubes are particle accelerators?! CERN is just a really big TV?
also, on the subject of TV, does anyone know why, if the “snow” in between channels is a soup of weak signals (big bang, baby monitors, harmonics etc) , does recorded “snow” keep moving when you press pause?
Well, a rather weak particle accelerator, but technically yes.
With better programming. :-)
excellent, i laughed!
When you saw “snow” on old TVs, back before they had auto-blanking, one in every-so-many of those dots is the TV picking up remnant radiation from the Big Bang.
That would be more impressive if I remembered the figure.
A CRT fires electrons from the guns at the back, electrons are particles (sometimes). Same operating principle as any other particle accelerator really. Also same principle behind X-ray machines, which is why kids who grew up in the 1950s have slightly transparent skulls.
This guy says 1%.
mmm.youtube.com/watch?v=ClDmjQo8nVQ
DEC CRTS from the 80s are bad about getting a fungus like growth in the glue that holds the shield to the CRT. Best way I’ve found to remove the shield is to take a 14″ length of stainless steel wire and connect each end to a car battery charger. That heats the wire up to red heat. Then slide it between the CRT and shield and it melts away the glue.
Cool, indeed one of the DEC (VT320 IIRC) terminals we have at the computer museum here suffers very badly from this. Might have to do this at one stage as it’s unusable right now.
nichrome wire, not steel
I never used nichrome wire – don;t have any around. But I can personally attest that stainless steel wire retains enough strength at red heat to get the job done without breaking.
For cleaning off the remaining glue, if both sides are glass, I would use Goof Off. It’s very good at removing adhesives, but it will melt plastic, so you have to be careful what you use it on.
Where do people still find those vintage terminals? My father had one of those Lear Siegler ADM-3A terminals in his business at one time (attached to climate control system). I tried to find one again for nostalgia reasons, but at least in Europe they seem to have disappeared completely or have exceedingly high asking prices on epay. Or maybe I am just looking in the wrong places….
I wonder if perhaps a modern quality “clear bra” from a car would work as a suitable replacement. The glues for them now are made to be strongly UV resistant, and you can get them as thick as 14 mil right now – though of course, that’s probably serious overkill.