Author Topic: AGING LCD w/DARK SPOTS (Read 5793 times)

PKTKS · « **on:** May 20, 2018, 05:05:26 pm »

Hello ...

I have an old DMM on my collection that started to show some "DARK SPOTS"
under some angles.

Depending the viewing angle the spots are more darker.
It is an old item with "sentimental" value on the stock.

Investigating the issue I have seen that the spots are inside the back part of the LCD

Wondering if there is a SAFE METHOD OF CLEANING THESE SPOTS.
DAMAGING even more attempting to clean will not help.

One photo should tell all about. The spot is even darker from this shot

Any help welcome

Paul

james_s · « **Reply #1 on:** May 23, 2018, 01:02:12 am »

It looks like the polarizing film may be damaged, or possibly delaminating, there's one on each side of the glass. It could also be some of the liquid crystal compound has leaked out of where it's supposed to be but usually that results in a dark splotch. I would recommend being careful as it's easy to damage it worse than it is already.

Shock · « **Reply #2 on:** May 23, 2018, 06:05:20 am »

If old the LCD bezel inside will be very brittle, especially screws and mounting clips, I know as I've split one whoops (looked even better after I replaced it).

If you havn't check the clear plastic in the front shell, I've opened some and it's not the LCD so much as the plastic cover is dusty and hazed on both sides, which makes it look far worse. Something to also consider is if it's overheating from nearby components on the PCB.

PKTKS · « **Reply #3 on:** May 23, 2018, 03:37:03 pm »

Thanks a lot folks for the ideas...

I have already dismantled all the LCD to have some clue.
Have also contacted the manufact. - guess the answer ?

** AS THIS METER IS OLD (more than X years) we have no parts for it... **

GREAT support.

While dismantled with care... my best guess is that they used some
sort of "GLUE" in the back side of the LCD.

That glue or stick back plane is getting darker and darker...

Some research (aka google) gave me one or two tips about 'ripping' that
back plane and "cleaning" that glue or adhesive or whatever.

But you known.. ISOPROPANOL or ACETONE are damn strong chemicals.

Using force on the back of an LCD... may destroy the thing...
So.. that's it I have done nothing.. but the spot gets darker

Paul

Shock · « **Reply #4 on:** May 23, 2018, 04:23:58 pm »

Quote from: PKTKS on May 23, 2018, 03:37:03 pm

Using force on the back of an LCD... may destroy the thing...
So.. that's it I have done nothing.. but the spot gets darker

If it has sentimental value I can only suggest to be safe get a spare then repair. If you manage to get it working sell the spare off or keep it for parts.

Get used to companies not keeping parts after so many years.

PKTKS · « **Reply #5 on:** May 23, 2018, 04:33:08 pm »

My idea as well .. contacted the manuf. but they have no replacement for *ANY* LCD

Prob. they import some batches from China in the just number to production.

No spare parts. None as they answered me.

Another folk in youtube managed to "clean" a back plane adhesive...
But he didn't posted the product used.

Anyway. scratching may get things useless - so far it is perfect - aside the dark spot.

And yes it is a really sentimental piece in the shelf...
Paul

Shock · « **Reply #6 on:** May 23, 2018, 05:44:39 pm »

Let us know what it is and take a full photo? Perhaps someone has a broken one or knows another model that the screen is used in. If it's below a certain cost or rebranded yeah absolutely they won't keep parts. I'd not even expect them to, been that way for years.

But there is an upside, usually more stuff for us to fix for cheap. I'm still enjoying my ~~$300~~ free coffee machine and I've not even repaired it yet.

PKTKS · « **Reply #7 on:** May 23, 2018, 06:04:04 pm »

i will try to find some time to take apart the LCD.

The thing dates from mid 80's may be very early 90's
when I got it was kinda "new stuff" at the time.

It is not so well put together like today's DMMs
and take apart the LCD requires some calm and patience.

I doubt there will be another LCD.
but cleaning that crappy stuff that is darkening may be still feasible

Paul

SeanB · « **Reply #8 on:** May 23, 2018, 07:52:49 pm »

If the LCD is a standard one, 1999 with a few annunciators and a sign, plus decimal points ( and probably a colon between 19 and 99) and has pins and not a zebra strip connection, then you probably can look at RS or other suppliers for a similar LCD display of the same size, as the layout for these is very standard, simply because of the need to have the pins laid out without any vias on the glass. Same height display will very likely fit there, though you might have the odd non original annunciator flag. If it is a Zebra strip version you probably will also find one that size that fits.

Otherwise the only way to remove the polariser is to first use a little heat to soften the adhesive, and then use a straight razor blade ( Minora blade as used in non cartridge straight razors, generally a cheap item sold in packs of 5 or 10) with some protective tape applied to the one half to protect your fingers, and gently slide under the edge to remove the plastic film from the glass. then you need some new polarising film for the display, which might be hard to get unless you are successful in removing it off another display.

PKTKS · « **Reply #9 on:** May 24, 2018, 06:00:57 pm »

Here some shots taken today

- The LCD is housed with 2 zebra strips.
- The back plane contains a white stick
- My guess is that adhesive glue is causing this
- You can see some points and strips on the adhesive

How to remove that stick and clean the LCD... ?

Paul

PKTKS · « **Reply #10 on:** May 24, 2018, 06:02:13 pm »

Taken apart it can be cleaned just fine ...

Question is which product and how to remove the white stick

PKTKS · « **Reply #11 on:** May 24, 2018, 06:03:19 pm »

Note the white "STICK" glued in the back..

It is full of spots and dark shadows...

PKTKS · « **Reply #12 on:** May 24, 2018, 06:04:06 pm »

Under a strong light you can see the effect of the shadows.

PKTKS · « **Reply #13 on:** May 24, 2018, 06:05:09 pm »

Back in business just fine.

Apart the dark shadows the thing is pristine

Paul

rsjsouza · « **Reply #14 on:** May 24, 2018, 06:43:09 pm »

Paulo, I see in the PCB it is a VC9808, which is still sold around.

Perhaps you could buy another VC9808 and replace the entire display?

There is one at Amazon that is reasonably priced. With the import taxes in Brazil (and hope the DRF agents don't simply steal it) that shouldn't cost too much. After all, since it has sentimental value, no price is too high!

PKTKS · « **Reply #15 on:** May 24, 2018, 07:45:17 pm »

It is indeed the PREDECESSOR of VC9808.

It was Re-branded here by 3rd part company
The chipset may still be the same UM7108F.

The VC9808 has a much better LCD with APO and backilght
and other goodies.

One more shot left to show the spots inside the adhesive layer.

rsjsouza · « **Reply #16 on:** May 24, 2018, 08:32:29 pm »

Which Minipa or Icel multimeter is this? Having the model can help find the correlated Chinese one.

PKTKS · « **Reply #17 on:** May 25, 2018, 10:33:03 am »

This is the first release of Minipa rebranded VC9808
more or less based very first implementations.

The REAL VC9808 has a MUCH MUCH better LCD

It appears by the call VC9808 a bit later

Paul

PKTKS · « **Reply #18 on:** May 25, 2018, 02:57:29 pm »

A strange detail about the "CODE" or IDs on the parts...

Is that the stamp on the PCB has absolute nothing to do with the real date
defacto I have acquired this piece.

2000 is WAY AHEAD the early 90's when this was purchased.

By that time only 2 or 3 brands were re-branding this PCB which
then by late 90's became available by at least a half dozen re-branded others

You can see that as if 2000-XX-YY - by no means this board is so new as that

And the call "VC9808" was not available as it were by early 2000's
The model branded as VC9808 is far superior from one on this board

and that excludes the possibility of using that LCD
because it is better and more complete - unfortunately

Paul

rsjsouza · « **Reply #19 on:** May 25, 2018, 06:47:34 pm »

Depending on the amount of anunciators on the display of your meter, you can try to adapt a modern version as mentioned by modemhead at his blog:
http://mrmodemhead.com/blog/fluke-8020a-lcd-replacement/

I did this to my dad's 8020A and it works quite well.

LateLesley · « **Reply #20 on:** May 25, 2018, 07:12:14 pm »

Just to throw the idea out there - did you ever watch Dave's video on designing an LCD? If you're really stuck, could you re-do the LCD design, and have a few manufactured? You could then keep 3-4 for yourself, and sell the rest as replacements for other folk looking for these? I know Dave talks in 1000s, but maybe you could get a small run.

Just chucking the idea out there. But it probably would be more expensive than you want to do.

PKTKS · « **Reply #21 on:** May 26, 2018, 01:28:41 pm »

Yep i have seen these customized LCDs

But you see... this is not some sexy brand "top thing"
like Agilents Flukes LeCroys..

It is a plain cheapo FIT ALL PURPOSE DO IT ALL

The thing with CHEAP meters is that you can have 2/3 even 4

costing 1/10 of a sexy Agilent or Fluke - and that cheapo does
exactly the same thing by the end of the day.

If the cost to repair this tool is beyond the intrinsic value...
You drop in another.

My thing w/this tool is that it already last a very long of reliable service
worth 1000 times the cost. No problems besides the aging (GLUE) LCD

I am very inclined to think that is only a matter of removing that nasty glue
If a thermal iron can "remove" the glue (like some phone screens glue) that would fit

I am not sure if the LCD will support the heat of the iron.
Once removed i still will have to "CLEAN" the glue left over.

You see. COSTS NOTHING.

That is the thing of CHEAPOS.

SEXY Agilents or thousand dollars Flukes may worth the hassle
or the cost of repair - not the case

CHEAPO as half dozens are another class of tools

They just do the job. 1/1000 the price

Paul

PKTKS · « **Reply #22 on:** May 26, 2018, 01:34:19 pm »

Unlikely the 2 zebra strips will fit another more modern LCD

Possible but very unlikely to find one

Still considering alternatives to wipe out that nasty dark glue on the back side

Paul


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Author Topic: AGING LCD w/DARK SPOTS (Read 5793 times)

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