LCD display failure mode - Page 1
Forum section: electronics / general

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: January 29, 2024, 12:31:05 pm
content: Just out of interest - what is the failure mode for the LCD display shown in the attached picture?BT

author: MathWizard
author_rank: Super Contributor
timestamp: January 29, 2024, 03:08:48 pm
content: Do you know it's history ? Did it just stop working, or did someone sit on it ?Is it some optical effect after the screen was crushed, and the liquid crystal spreads out like that ?

author: wraper
author_rank: Unknown
timestamp: January 29, 2024, 03:12:05 pm
content: Is it like this when staying not powered for a longer time or it becomes normally blank? This could have nothing to do with LCD itself but the fact its not driven properly.

author: AVGresponding
author_rank: Super Contributor
timestamp: January 29, 2024, 05:12:54 pm
content: I'd guess it's a burn mark from the CCFL backlight.Burn is a strong term for this really, it's more a heat-cycling over time, that changes the optical properties of the diffuser/polariser.

author: ataradov
author_rank: Super Contributor
timestamp: January 29, 2024, 05:31:59 pm
content: This is a very common failure mode for old LCDs. It happens even on devices without backlight or heat exposure, just over time. There was a post on this forum from a few days ago about similar issue with some HP calculator.I don't know the exact reason for this, but I don't think there are solutions for this. In some cases people made reproduction LCDs (TRS-80 Pocket Computer is one such example).

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 29, 2024, 09:03:45 pm
content: Yes:https://www.eevblog.com/forum/vintage-computing/my-hp48g-has-developed-a-fault-(display)/This very much looks like the same thing: most likely the polarizer that got detached around the center. It's relatively common indeed.Depending on the construction of the LCD display, the polarizer may be accessible right on the back of the display, in which case you can try removing it and replacing it with a new one, but it's not really a picnic (you'll find some videos about that on YT, eg.)Sometimes though, the polarizer is sandwiched between two sheets of glass, in which case the repair is kind of a lost cause.Could you open the case and take some pictures of the LCD display?

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: January 30, 2024, 02:34:15 pm
content: Thanks for the replies. I wasn't considering a repair, and the unit appears dead. It is a Sharp PW-9100 just for info. I have no idea of its history as it came in a large box of leads, wall warts, guitar tuners, cameras and vintage Japanese-to-English dictionary PDAs etc. These last included 3 unused Casio Ex-Word Dataplus 3 units. Probably worth zero these days but I will save one with my old calculator collection!I will tear the Sharp to bits to have a look at the polariser etc just to educate myself.Sorry, I missed the identical issue with the HP calculator!Regards, BT

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: February 01, 2024, 04:33:02 am
content: Just to close this thread:I dismantled the Sharp electronic dictionary. This LCD display does not have a backlight. The two layers of glass which comprise the display have a thin translucent matte film bonded onto the back. Behind this is a copper/gold-coloured film that seems to be a reflective surface, although why it is copper coloured and not mirror is not understood. The translucent film must be to stop a reflection of the text on the LCD appearing as a 'shadow' reflection behind the image beacuse of the gap between the glass and the reflective layer. Behind these layers is a thicker opaque plastic layer (not bonded to the display) probably as some sort of protection for the back of the thin reflective layer. The 'failed' area is actually inside the two layers of glass so probably the polariser as suggested above. I had not examined this type of display before although it must be common to most calculators etc that don't have a backlight and rely on incident light.Regards, BT

author: Ian.M
author_rank: Super Contributor
timestamp: February 01, 2024, 06:02:44 am
content: I've also seen failures with similar external appearance due to the metallisation on the reflector failing. Its often an aluminumized plastic foil, and with age (more rapidly in a humid environment), the aluminum surface film can oxidise from the edge inwards to a translucent aluminum oxide layer, vastly reducing the reflectivity. If the segments still display enough contrast under strong oblique light, it may be possible to replace the reflector foil