Laptop backlight issue

[stevo1210]

I've been having this problem with my Toshiba P25 laptop recently. The screen backlight won't come on at times. There's a standby switch around the left corner of the palmrest towards the screen. Basically it is a switch that once pressed the backlight turns off and when released the backlight turns on If the backjlight doesn't come on and I jam that up and down a few times the backlight comes on and works.... I have a feeling this may be a dirty switch? Am I correct in saying this?

Thanks.

[NxB]

Re: Laptop backlight issue

Could be. Or the little switch that turns off your screen when you close it. Some microswitches you have to actually replace. Once you take them apart its harder to get them back together than just soldering on a new one.

[stevo1210]

Re: Laptop backlight issue

I'm wondering if the screen cable is busted or not? cause in addition to the backlight issue, the screen sometimes goes fuzzy and it goes back to normal once you tap the area where the cable connector is located. Re-plugging that screen cable solves the issues for maybe a few days and then it does it again...

[ratdude747]

Re: Laptop backlight issue

since the backlight control signal is likely on the video cord, that might be it.

[pentium]

Re: Laptop backlight issue

Try replacing the switch.
If that fails, try replacing the inverter.

[stevo1210]

Re: Laptop backlight issue

since the backlight control signal is likely on the video cord, that might be it.

i have a gut feeling that might be the case.

[PCBONEZ]

Re: Laptop backlight issue

Do you have a single cable to the screen from the chassis or two+?

[Krankshaft]

Re: Laptop backlight issue

Yank the battery and check the switch with a continuity tester for intermittent operation.

The backlight and video signal harness are usually kept separate to prevent interference.

To turn the backlight on there is usually a separate BL ON input to the inverter that voltage is applied over.

The backlight VCC and GND are always connected when 5 volts for example or possibly VCC switched by a transistor (voltage varies by inverter) is applied to BL ON the inverter starts.

Backlight brightness is controlled with another separate inverter input a variable voltage from 0-5 volts for example controls the brightness no input 0V allows full brightness.

I'm making a few generalizations but laptop inverters are surprisingly similar to each other only varying a bit in circuit design and in size due to the size bulbs they drive.