Electronics > Repair
LCD display zapped by static discharge, repairable?
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Buriedcode:
Those nice PCB photos! (often we see blury ones here..).

From what I can make out, theres a resistor divider, with 10k going to pin2 of the display (5v) and 330 ohm to pin 1 (ground/0V) that provides the voltage for pin3 - the contrast pin.  So with 5V on the display thats 330/(10k + 330) * 5 = ~0.16V.  Generally the contrast voltage on these can be anywhere from 0.1 to 0.7V so its within range, but looks quite low to me.

Putting a pot in parallel with the 10k resistor - as you did, between pin 2 and 3, thats between 5V and contrast - reduces the value of that resistor, which should raise the contrast voltage and give better results - again, exactly as you did!  If your value of 1070 ohm was correct (I don't doubt), then in parllel with a 10k resistor makes it pretty much 1k.  With the voltage divider that would make the contrast voltage .... 330 / (1k + 330) * 5 = 330/1330 * 5 = 1.24V.  Quite high, but hey, if what you've done improves contrast, it works.

The faded pixels, to me, just look like age.  STN LCD's tend to last a very long time, but things like humidity and wild temperature changes over long periods can damage them.  I've lost a couple of old 90's 240x64 displays when I stored them in my garage.  I think about 8 winters killed 2 :/

If you were to replace it, it looks like they don't use the mounting holes but hold the displays PCB in place with plastic  hooks - so the dimensions of the display are important (98 x 60mm).  I'm almost certain the pinout with be the standard 16 pin one. 

The only odd thing is the backlight... it has a nice blue backlight, I haven't seen too many with that exact colour, so I'm guessing its an EL (electroluminescent) backlight - that might be what the small yellow transformer is on the PCB.  EL backlights are very pretty, but a bit of a sod to drive (400Hz relatively high voltage).  And have largely been replaced by LED backlights (run on 3-5V, easy to drive/dim, and are bright and efficient).   Again.. I could be wrong hewre, the transformer could just be part of the units power supply.

So replacing the display might mean a different backlight - theres some blue STN ones with white pixels and blue backlight, as well as negative mode (dark background, pixels the colour of the backlight) . If the unit can control whether the backlight is on or off, then it could require some mods to get this to drive an LED - but if its on permenantly, then you could just connect to the 5V line if it doesn't draw more than 50mA.

But if you're happy with it, and its readable, then its a job well done  :-+   And if you like the device, then its always worth giving it a shot.  I value things more when I've repaired them.

Well done dude  :-+
Divarin:

--- Quote from: Buriedcode on April 06, 2022, 07:06:14 pm ---So replacing the display might mean a different backlight - theres some blue STN ones with white pixels and blue backlight, as well as negative mode (dark background, pixels the colour of the backlight) . If the unit can control whether the backlight is on or off, then it could require some mods to get this to drive an LED - but if its on permenantly, then you could just connect to the 5V line if it doesn't draw more than 50mA.

But if you're happy with it, and its readable, then its a job well done  :-+   And if you like the device, then its always worth giving it a shot.  I value things more when I've repaired them.

--- End quote ---

The backlight is only on when you first start up or for a couple of seconds after you press a button.  It has always made a high pitched wining sound while the light is on.  Yeah I'm not sure I fixed it "correctly" but somehow managed to make it work and since my use case for it now isn't going to be carrying it around on walks or anything, just using it to feed data into old vintage computers it should work fine.

I had this thing in a box in the closet for probably 8 or 9 years now because I knew I wanted to get it going again but had no idea what could be done.  But over the past few years I've been dinking around fixing up old computers and stuff and have gradually been building up some skills (still a long way to go) but I felt confident enough to at least try. Just needed some of the experts on this forum to point me in the right direction, I didn't even consider that there might be a contrast adjustment.
Buriedcode:

--- Quote from: Divarin on April 06, 2022, 08:12:17 pm ---
The backlight is only on when you first start up or for a couple of seconds after you press a button.  It has always made a high pitched wining sound while the light is on.  ...

--- End quote ---

Yeah that'll probably be an EL backlight then.  Difficult to replace, but it seems to be working just fine, so no need.

Repairing, or just "investigating" devices, taking them apart, see how they work, and googling questions it raises is a great way to learn.  And this forum is great for that, getting pointers to the right direction, when one is unsure what exactly to google.

Apologies if my posts were too detailed, or off topic, I get carried away with explaining stuff or trying to work out how things work.  Glad its all working!
DavidAlfa:
Definitely EL.

These displays are easy to disassemble, shouldn't be hard to transfer the EL to the new display.
Just ensure to remove any LED resistors.
james_s:
Careful with EL backlights, they'll give you a good zap. Won't kill you but it doesn't feel good either.
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