dylanfm wrote on 2026-04-03, 11:14:

I'm sure this is a long shot, but does anyone have any info about the LCD and/or backlight driver board for an L40SX? Schematic […]
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I'm sure this is a long shot, but does anyone have any info about the LCD and/or backlight driver board for an L40SX? Schematics, connector pinouts, replacement part sources?

I picked this L40 up and the display is blank/black. The person I got it from said something about the contrast slider was initially flakey and then kept trying to get the contrast right and now he thought the contrast was stuck all the way dark, which could be the case. There is a lightish border around the edge of the LCD and the rest of it is completely black. The border brightness varies if you move the brightness slider, but the contrast slider doesn't seem to do anything. I was hoping that if I took it apart I would find a bad pot, but that doesn't seem to be the case. I'm not really sure if the backlight driver board is the problem or not. The contrast and brightness sliders are on that board, but I'm not sure how changing the backlight would effect contrast, so maybe it just passes that signal on to the LCD. There is a connector that I think is power in and then another that goes over to LCD PCB itself. Or maybe something else is wrong with the LCD itself?

When I hook an external monitor up that works fine and it also causes the LCD to go completely black (no light border).

I would really like to get this display working, but tracing the signals through without a schematic, especially with components on the board that aren't clearly labeled, is really daunting.

Check out Silverstron's video on the L40SX, he shows recapping the Brightness / Contrast board and seems to have experienced exactly the same problem you're currently seeing 😀
https://www.youtube.com/watch?v=25p1IE5Ksgw
The caps on the mono LCD panel itself look like ones that don't fail so much, but the low-height caps on the brightness / contrast board are absolutely the type & time-window to leak.

The brightness / contrast board either generates or controls voltage levels (-20 to -30v I think?) for the liquid crystal to display and vary the contrast. If the contrast circuitry of that board isn't functioning then you would get a black screen like you're seeing.

Thank you so much! That looks exactly like what I have going on. I'm not sure why I hadn't seen that video before. I'm going to give it a shot.

Replacing the caps on the backlight driver board seems to have fixed the contrast issue. The display is now readable and looks fine. The brightness adjustment doesn't seem to do a lot, but like I said, the display looks fine, so maybe it is working enough/correctly so I am fine with it for now.

Thanks again!

dylanfm wrote on 2026-04-04, 01:25:

Replacing the caps on the backlight driver board seems to have fixed the contrast issue. The display is now readable and looks fine. The brightness adjustment doesn't seem to do a lot, but like I said, the display looks fine, so maybe it is working enough/correctly so I am fine with it for now.

Thanks again!

The Brightness adjustment doesn't do much on any of my Mono LCD panel laptops, the CCFLs are either tired or they were never that bright in the first place 😀 They get brighter as they warm up so it might do more after that laptop's been on a while.
That's wonderful the screen is back to working, I've been trying to fix similar issues on a Toshiba T1850 lately and got nowhere with it to the point that I destroyed the LCD trying to fix it. Oh well.

yeah, it seemed like when the contrast was broken before the recapping the brightness slider had a bit more of an effect on the outside border of the screen, but maybe not. I do have to have the contrast slider pretty far over to one side to get a good display, but it seems fine.

I have a few old toshiba laptops that I should take a look at again. I was trying at least one of my old laptops working a few months ago, but no HDs were working and at the time I didn't have anything to make floppy disks with. With the aggressive accumulation of retro computer equipment I have made in the last month or so I should be able to get some of them working now.