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-   -   Acer GR235H partially losing backlight (https://www.badcaps.net/forum/showthread.php?t=84240)

spleenharvester 04-30-2020 06:01 PM

Acer GR235H partially losing backlight
 
Unfortunately my trusty GR235H seems to be on its way out. After a while I lose two backlight segments at the bottom of the screen, always the same two. If I switch it off and on again it will work and keep working for hours.

A couple of times it's also been completely black screen with just the power light (I haven't shone a light on it yet to see if it's actually displaying anything), and again has started working properly after turning off and on.

What kind of problem am I dealing with here? If it's an LED strip how do I go about replacing it?

CapLeaker 04-30-2020 06:55 PM

Re: Acer GR235H partially losing backlight
 
Those 2 LED’s are failing. The only 2 things you can do is to either turn the backlight level down, or replace those bad LED’s / LED strip.

spleenharvester 05-01-2020 10:20 PM

Re: Acer GR235H partially losing backlight
 
Ah thought so. I'm guessing these are within the frame of the panel itself, and not on the back like in TVs - is this easily done or do you think it's worth just changing the entire panel out?

spleenharvester 05-02-2020 05:09 AM

Re: Acer GR235H partially losing backlight
 
Also it just did the thing where the screen goes completely black again - just checked and there is an image, just no backlight at all - does this still suggest LEDs or is something else quitting too?

CapLeaker 05-02-2020 05:47 AM

Re: Acer GR235H partially losing backlight
 
the PSU part for the back light went into protection mode or one led went open in the string. LED's are current controlled, not voltage controlled. That's all right until one or more LED's fail, because LED's don't like to get more voltage that they are designed for.

spleenharvester 05-02-2020 07:12 AM

Re: Acer GR235H partially losing backlight
 
4 Attachment(s)
So plot twist, I've ripped it apart and found a bloated pair of Su'scrud caps. Unfortunately my picture-taking capabilities are about as high-quality as these capacitors, but it looks to me like they feed into the 2x OZ9998GN backlight drivers. Do you reckon it's worth recapping these and seeing if it fixes the issue (I'm just wondering what the odds are of two LEDs going out at once!).

The board is an L0256-1M, and doesn't seem to have been documented elsewhere on this forum. C121 and C818, screenprinted back and front on the board (corresponds to bottom-right of rear photo).

EDIT - added a better photo of the circuit

CapLeaker 05-02-2020 08:58 AM

Re: Acer GR235H partially losing backlight
 
I wouldn’t go specifically buy capacitors, but if you had some good used ones to pop in on hand from a junker board, go ahead and try. It will not fix the 2 LED out situation.

spleenharvester 05-02-2020 10:23 AM

Re: Acer GR235H partially losing backlight
 
Cool thanks, I'll give it a shot. I know it's a long shot but this panel has 4 current feedback channels with 2 LEDs on each, which as a layman makes me wonder if there's an issue with one specific channel. More than likely I imagine those two LEDs are kaput though.


Either that or the monitor will have to be scrapped, as I have zero confidence in my ability to access the LED strip :d

CapLeaker 05-02-2020 10:30 AM

Re: Acer GR235H partially losing backlight
 
You can tell which string is bad by measuring the voltage on each.
It makes a good project to learn.

spleenharvester 06-01-2020 10:51 AM

Re: Acer GR235H partially losing backlight
 
Replaced the caps with some equivalent Panasonics, monitor has been running fine for 24 hours continuously on 100% brightness. Hopefully it lasts.

spleenharvester 06-13-2020 12:04 PM

Re: Acer GR235H partially losing backlight
 
Just as a follow up for anyone who finds this in the future - monitor is still fine after two weeks of 24/7 at max brightness


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