Bleeding LCD displays

Years ago I used to visit the local tip to pick up TVs to refurbish, once I found a set that I only wanted the PCB from, so the quickest way to remove the wooden cabinet and all the other unwanted stuff was with my steel toecap boot - during this procedure, the faceplate fell off the CRT - its literally only glued on!

On another occasion someone I knew was minding the site while the regular bloke was away, I persuaded him to slowly advance the hydraulic ram in the compactor while I nipped a CRT diagonally across 2 corners between the ram and the opening in the container. Once I was safely out of the chute we switched the ram back on, the hydraulics did a great deal of heaving and grunting - meanwhile some bloke had gone up the steps to tip his rubbish, suddenly there was an almighty bang, the ground shook and the bloke was enveloped by a silver blizzard that used to be the metalisation inside the tube.

I've seen photos online of the aftermath of an implosion on a CRT production line - apparently its possible for one imploding CRT to set off a chain reaction that destroys quite a few.

LCD panels have a slots at the bottom of the glass to help equalize inside to outside air pressure. If it were sealed shut, your laptop or tablet display would explode at altitude.

One of my non-clever mistakes is to clean the screen of a warm running laptop display with a soapy water while in the upright position. As the screen cools, the soapy water is sucked into the panel via the bottom slots. Eventually, LCD leprosy forms along the bottom of the display. I have several panels like that, all from an office where the cleaning service washed down the LCD displays every night as part of the service.

I would speculate (which means I haven't tried doing this) that it would be possible to use the partial vacuum effect to replenish the liquid in the display. I have no idea what's in the liquid or where to obtain a supply. Just remove the lower part of the panel frame, heat the panel, dump into some warm LCD liquid, and hope that it sucks the liquid into the panel as it cools. LCD Panel Rejuvenator (patent pending).

The LCD panel manufactures could probably prevent the problem by simply adding a foam sponge along the slot to act as a reservoir.

Incidentally, the fluid is reputed to be sticky and toxic.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

so it seems the bands are shrink fit into place, and expanded with heat:

pickax to a CRT, indoors. safety equipment is an old blanket:

brick? to a weird "wide" CRT.

another stupid one, from the same clever folks:

As a kid I unwrapped the capacitors to find the interesting stuff inside all that wrapping paper. Never found anything, though... :-)

Leif

--

beslutning at undlade det.

When I was a kid, someone gave me a regen set in a very grand wooden cabinet.

When I'd finished breaking it - it was time to take it apart and see what's in it.

In a compartment under the one the chassis was in, there was a huge flat profile paper capacitor - one that big could only have been the HT reservoir.

Think of all the things I could've got up to with that if I hadn't unraveled it!

I dragged a huge transformer out of a TV set to grade school once to show people the huge sparks that could be drawn off one winding with a 9 volt battery. It was actually a fairly fat and impressive arc. The transformer was eventually confiscated. Boo.

Those old mains derived EHT transformers were probably even more lethal than a MO transformer.

For a B&W TV, 6 - 7kV was about average - not sure whether any CTV ever had mains derived EHT.

It was some sort of large gooped up with tar EI core thingy with one super high inductance winding. I still have no idea how it worked in a television. If they made 6-7kv was there then some sort of diode and cap multiplier to run the CRT?

The "oldest" TVs I sort of recall the inside of were Zenith consoles with remanufactured module system with the bizarro rectangular connectors and constantly changing color circuit boards.

it's oily for sure, and busted open LCDs smell bad but that may be from the 5000 layers of adhesive and plastic sheets that make them. Old calculator displays were a bit simpler, but still had a foul smell when smashed up.

AFAIK it was just half-wave rectified, the peak value whatever that was, ended up at the final anode.

Its a bit surprising when you think that generally, CRTs were long narrow defection jobs - some early homebrew sets had electrostatic deflection, maybe a few commercially produced sets too.

Is this why tubes like in oscilloscopes, which are electrocstatic are so long for their screen size? My current scope doesn't have the hump in the back for the end of the tube, but I suspect it's a normal CRT with a yoke and coils as well, since it's really just a small computer monitor.

Electrostatic focusing is much faster than magnetic, but not nearly so well controlled--you get a lot of aberrations, which grow very rapidly with deflection angle. The basic issue is that electrons that are closer to the plate get bent further than those further away. In an optical system, you can correct for this by using a combination of positive and negative lenses, but there's no such thing as a negative electrostatic lens.

It was a real parlour trick getting decent vertical linearity and good spot sizes with pure electrostatic deflection.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Speaking of optics - I remember a PC monitor with a slightly concave faceplate, that was a pretty substantial slab of glass, the things weighed a bloody ton!

Most of the components were house coded so it was frequently neccessary to board-swap from the growing accumulation of scrap units.

Was it possibly one of those Zenith flat CRTs that really did look concave? They were really weird looking, powered on or off.

Zernith made a 14" CRT for computer monitors with a flat face, anticipating Sony by about a decade. (The phosphors were laid down without the mask. The tolerances were so tight, that any mask would work with any faceplate, simply be dropping it into place.) Someone at work had one, and it did, indeed, look odd.

Sony compensated for that optical illusion with a faintly bulging screen. I have one of the 400-series WEGAs in my bedroom (it's been going strong since

2000), and you can see the bulge if you stand the screen and look downward.

Now you mention it I think they were zenith - there was a sort of flurry of people wanting them repaired, then they dried up as if they'd never existed.

Not long after that, CRTs in general went out of fashion.

I didn't miss those flat screens - they were bloody heavy!

The monitor wars from back then were amusing. Getting my first 15" monitor was a big deal, and they even had strange stuff like 16" monitors (Nanao made those). Quite a few of the Taiwanese computer monitors were actually pretty good as well.

Once they really nailed good displays for computers, the cheap and crappy LCDs flooded the market.

I'm typing up this message on a Dell badged Sony Trinitron made in Sep,

2000. The retrace lines are appearing so it's time for some new caps at some point.

Somewhere in the back of the garage I have about 8 CPD15s (some badged as Dell).

Since finding an analogue LCD TV with a VGA socket on the back in the bin room at the flats, the Sonys haven't got any nearer to being dragged inside and repaired.

I can't bring myself to tossing my monitor mountain, and most still work fine (that's why they are still here.)