Bleeding LCD displays

heh

That's been a problem with older LCD displays on Fluke DMMs as well. My old 8050A is starting to exhibit those symptoms, despite having been indoors all of its life.

It's ameliorated somewhat on mine when the display is energized for a few hours; the dark areas retreat and become somewhat dimmer. Not a permanent solution, but you might try that. Hook one up to an external supply (they are battery powered?) and let it run over a weekend to see if there's any improvement.

There are several hacks around the 'net where folks have replaced the LCD module with a bank of 7-segment LEDs. What I'll probably try is to fit an EADog 1x8 LCD module in place of the original, with a small micro to handle the display initialization and character translation. The EADog is 55 x 31 x 2 mm, a good fit for the 8050A.

This display is actually on a CD unit. Its not been used for some time so may be what you say. Its also on the lower part of the display, perhaps turning the CD upside down, when not in use, may help. At the moment the black splodge is not intruding into an information area, but I assume it will eventually

I don't think gravity helps... The display on the 8050A here is darkening from the top, down. Looks almost like mildew/fungus growing down from the top, intruding into the spaces between the segments.

Apply 30 atm in a pressure chamber, then wait a few hours.

makes some sort of sense, I always assumed the sun-heating business was making the fluid expand and force open the seal between the glass sections. OK, so apply your high and even-handed pressure but how to stop the glasses separating again?

The fluid tends to stay in place,it likes the glass sheets. Years ago I made lcd glasses, to switch the visual field in experiments. Production:Separate the glass with a thin mylar film(dupont), glue two opposite sides with 5 min epoxy, remove the mylar, then put a small drop of lcd fluid on one of the open sides. And a miracle happens, the drop gets sucked between the glasses(~10 minutes) very slowly. Then clean the open sides, and apply epoxy to them as well. Worked for me. So only pressure or heat tends to drive the fluid out. Bad mounting can cause unwanted pressure and damage.

The air pressure repair works, if the fluid is still present around the leak, else you are out of luck.

I could see using a vacuum pump first (LCD in a bath of fluid) to draw out any air. Then, with the LCD still bathed in the replacement fluid, pressurized to the 30ATM to force the liquid back in. Then seal with whatever works best.

John :-#)#

If I can find a salvaged one that has bled over time, I will try covering the pins with card and then a bicycle inner tube each side of the glass,held in a vice and inflated, and see what happens. Then leave it for a few hours, then release pressure and see what happens over the months

You cant replace the fluid, the pressure treatment just tries to force back in what was there in the first place. Maybe. The fluid had a price tag of >500 dollars for 4 cubic centimetres, and has wildly different specs for various lcd's, so forget getting new fluid. My lcd's switched between transparent and milky, and did not use polarization.Working voltage 500 volt AC!!!!! on/off.

Also checking the mount for unwanted pressure points does improve things.

no change with unconfined inner tube pressure. Decided to squash the LCD (no pins attached to this one) between 2 pieces of silicone rubber in the engineering vice. Cleaned the rubber but did not think to clean the vice faces or add some card or something, must have been a bit of grit and crack, so end of that experiment. I only found one salvaged LCD wiht a black splodge

Same on my Sharp EL5100 calculator - it was a present in my college days and has sentimental value, otherwise I'd have binned it.

Apparently there are salvage LCD panels out there, but hard to justify the cost when I have a pile of calculators in assorted shapes & sizes.

Once I repaired TVs for a back street bodger - a CTV came in with a rainbow pattern on the picture and no amount of degaussing did any good. For some reason I up-ended the TV, the picture improved a lot, so I turned it completely upside down and the picture was perfect.

We took the CRT out and put it back upside down, then slackend the yoke clamp and rotated that 180 deg, the purity rings needed a tweak but all was well - so we wedged a lino tile between the anode cap and PCB to stop it cracking over, and cased it up.

I have a calculator with "black clouds" gathering along the top edge of the LCD.

Activating any segment/symbol clears a halo around it for a while.

When I asked about this on various groups a while ago - a few people suggested failing edge seal letting moisture contaminate the liquid crystal.

Ah, thanks, that clears up why no-one is resurrecting them...

John :-#)#

If there are pressure points on the LCD panel, the effect should vary if the outer casing is flexed.

My calculator that has gathering clouds at the top of the LCD spent a fair bit of time in my back pocket - the suggestion of cracked edge seal and moisture ingress is possibly right.

That reminds me of when people actually rebuilt or replaced picture tubes. Any good stories of tubes imploding?

I found another black splodged LCD, placed inside 2x sheets of silicone rubber inside 2 slabs of cleaned thick perspex sheet in the vice and left over night. Splodge in one area broke into a pretty dotty fractal pattern over the whole display, then over minutes a fractally natural fern-like spots . Have not so far managed to activate any segments, assuming backplane is an end contact. I suspect the black will coaelesce back into a solid area over the next few hours

I always made the scrap ones safe by knocking the neck off.

I'm aware of one guy that broke a neck off, by accident at a shop, but nothing past that.

I've got to check you tube for vidoes of people removing the steel band around a CRT. Not sure how you'd even weasel under one to cut it off, and from a safe distance, but somebody somewhere has to have tried.