Electronics > Repair

LCD display zapped by static discharge, repairable?

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Divarin:

--- Quote from: Audiorepair on April 06, 2022, 10:33:24 am ---I remember many years ago finding a solution to replacing a display where the contrast voltages were different.
I discovered that soldering a standard 1N4148 diode between contrast pin and ground gave around 0.6v contrast voltage, which happened to be perfect.

There must have been some kind of pullup resistor or circuit on the display that enabled this to happen.

--- End quote ---

Just read this after posting my last reply, if 0.6v was the correct voltage for you then my 0.4v isn't so suspect afterall, still I guess it wouldn't hurt to try temporarily replacing that with a pot and adjusting it to see if it affects the contrast.

Divarin:
Hey I had some luck!  I put a small pot initially set to 10k between pin 3 and pin 2 because I noticed direct continuity between pin 2 and the "input" side of the resistor before pin 3 so this seemed the easiest solder point and would also mean I wouldn't have to remove the resistor for now, just bypass it.

Powered it on, initially nothing seemed to happen I had to turn the pot quite a lot but eventually the contrast came in normal.  I desoldered it and measured the resistance: 1070 ohm, so about 1/10th what the original resistor is doing. 

I might just add some wire and keep the pot there but position it someplace more convenient.

I don't think the 10k resistor is zapped I think something changed about the screen when I zapped it which makes it now require more voltage to bring the contrast up to normal than was needed before.  So replacing the screen (and removing the pot) might work but also I can try just keeping the pot in there for now and if it doesn't get worse over time then I'll be content with it.

amyk:
https://huizhouteneng.sell.everychina.com/p-108658268-4-x-20-characters-lcd-display-ssc4a20dlnw-e-p-s4a20ct-e1-white-led-side-backlight.html

This specific part is still in production, apparently.

Divarin:

--- Quote from: amyk on April 06, 2022, 01:47:09 pm ---https://huizhouteneng.sell.everychina.com/p-108658268-4-x-20-characters-lcd-display-ssc4a20dlnw-e-p-s4a20ct-e1-white-led-side-backlight.html

This specific part is still in production, apparently.

--- End quote ---

Yeah that link was the only source I could see but it looks like there's a minimum order of 500.  I might be able to get it (or one compatible with it) somewhere but if I can get by using the one I have then I'd rather do that.

Divarin:
Well the pot fixed helped a lot.  You can tell there's some kind of damage to the screen but after tweaking with the pot I got it to look pretty good.  It went from "can barely read it" to "can barely tell anything's wrong with it":




Thank you everyone for the help.  There's still a lot to do to refurb this thing but this issue was the "is this even going to be worth trying" issue.  Now, it's worth trying :)

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