I've got a couple of bleeding LCD's. No replacements available, so it's gonna cost me ~ $1K to replace the equipment. One's in an _old_ Fluke DMM, so that's not all bad, I get to buy a new meter. :-)
Ok, now to the questions: What's the average life of a properly used LCD? What causes the bleeding? Does the glass de-laminate or something?
Ed
I've never heard of an "average life" of an LCD. AFAIK, failures are generally caused by abuse. I have a couple 20YO Fluke 77s that are still going strong.
Sounds like the lcd got DC.
An LCD is layer of liquid crystal, with a well-defined thickness, sandwiched between two sheets of glass
"Bleeding" presumably refers to the liquid crystal leaking out from between the edges of the two sheets of glass.
Back when I was interested, there were basically two ways to seal the gap around the rim of the display - either a bead of epoxy resin, which would set at room temperature or a temperature not all that much higher than room temperature, or a bead of glass frit, which had to be fused to make a hermitic seal.
The temperatures required to get a glass frit to melt and fuse to form a hermitic seal are higher than those that that liquid crystal materials can survive, but you can fuse a frit with the liquid crystal in place if you apply a source of very intense and localised heat that can melt the outside edge of the frit before the inside edge has a chance to warm up to a destructive temperature.
Epoxy seals were cheaper back then and frit seals more expensive but more robust.
-- Bill Sloman, Nijmegen
Don't know about average life, but there was an early series of benchtop fluke dmm's that were well known for lcd failure as you describe. I scrapped two because of this problem. Have also seen it on some early racal hf receivers, but it's quite uncommon otherwise ime.
My guess was a faulty design or manufacturing process, as most good quality lcd's seem to last forever...
Regards,
Chris
On a sunny day (Wed, 25 Nov 2009 19:10:26 -0500) it happened ehsjr wrote in :
Once had a watch. left it in the burning sun, LCD went black... And stayed black. Same with a old GSM phone, but somehow it reversed itself to normal. So maybe it can be fixed? AC to shake the polarization back to normal?
IIRC sticking it in the freezer for an hour or two (at your own risk) may do the job.
What were the typical operating and storage temperatues?
Also, if it changes operating temperatue rapidly. Namely, in and out of direct sunlight.
And for other posts, AC or DC doesn't matter if the liquid crystals are not supposed to be there.
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