Member Avatar for DaveSW

I have a toshiba laptop s2800-200 (naturally the model doesn't exist on toshiba's website)
Whenever I plug in the mains adaptor the screen backlight goes off.
If it's running on battery it's fine.
Is this a software setting or a failed item of hardware?

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A few focused diagnostic notes for 's S2800-200 thread. The key clue is that the backlight dies when the mains adaptor is connected but works on battery. As suggested, checking behaviour during BIOS/POST is the simplest early split: a backlight that stays lit through BIOS points toward software or power-management interaction; one that goes dark during early POST (as reported) is more likely a fault in the backlight power path or sensing circuitry.

A short list of safe, noninvasive checks:

  1. Confirm OS power settings and any OEM power/eco utilities are not set to change display behavior when AC is present; boot to Safe Mode or a Linux live USB to rule out drivers/utilities.
  2. Observe BIOS/POST: pause at POST or hit the BIOS key repeatedly to see whether the backlight stays on. When POST is too brief, attach an external VGA/CRT monitor to check for continued video output.
  3. Test power sources in three states: battery only, AC only (battery removed), and AC+battery. Differences help isolate a bad adapter, DC jack, or mainboard routing.
  4. Perform a flashlight test: with the backlight off, shine a bright light at the LCD—if a faint image is visible the panel and GPU are functioning and the issue is the backlight/inverter.
  5. Measure the adapter with a multimeter or try a known-good adapter to rule out improper voltage/current.

If an external monitor shows image while the internal panel is dark, the problem is almost certainly the backlight power train (inverter for older CCFL panels, the lamp itself, or the panel cable). If both internal and external displays go dark when AC is plugged in, suspect the DC-in jack, power regulator, or mainboard sensing that disables the inverter. Older Toshiba designs commonly used CCFL+inverter arrangements; those inverter boards carry high voltage, so disassembly has a shock risk.

Given 's concern about opening the case, reseating connectors and completing the noninvasive checks above is recommended before panel or inverter replacement. Typical repair order: confirm software/settings and adapter, reseat LVDS/inverter connectors, test with a replacement inverter (if available) before replacing the LCD panel, then escalate to mainboard diagnostics if necessary. Documentation of which source combos (battery/AC) produce the fault will speed any shop diagnosis.

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Member Avatar for alc6379

It could be a software setting. I don't remember offhand, but there are things in Windows that can configure that. To test if it's a hardware thing, though, does it do it in the BIOS? If so, you might be looking at a motherboard replacement on that unit.

Member Avatar for DaveSW

It takes about a second to go off after you turn it on, so I couldn't say whether or not it had passed bios at that stage. Probably not.
Looks like a shut up and put up job to me ;-)

Member Avatar for stretch28

It takes about a second to go off after you turn it on, so I couldn't say whether or not it had passed bios at that stage. Probably not.
Looks like a shut up and put up job to me ;-)

Hi Dave,
I had to sign up for this forum as I have experienced the same problem with my laptop. I came across the following links and they should be able to help you out:

I have not tried either but I am going to give it a go.
Good luck!!

stretch28

Member Avatar for DaveSW

Thanks Stretch28 - those look interesting.

Member Avatar for stretch28

Thanks Stretch28 - those look interesting.

I tried to access the inverter on my friends Tosiba 2450 and could only find 2 screws - I think that I will take it to the pro's as I cannot afford to screw it up :confused:

Good luck with yours.

Member Avatar for DaveSW

Yeah - it's kind of tough to take a working machine and say "well it might not work when I've finished with it..."

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