Toshiba Satellite L40 backlight problem

Hi pals

I've got a Toshiba L40, mainboard TERESA20 REV 2.1 with a weird problem.
The backlight blinks but it's ok, I've tested it with a CCFL tester and it
works very well. So I've moved for the inverter, changed it with a brand
new one and nothing.
Can someone point me a direction cause I don't have enough points to
download it's schematic.

I've knowledge on electronics :)

Thanks for your attention

Around the LCD cable socket must have a fuse. Look healthy.

Checked and is ok. The backlight lights up but flicks. Just like a strobe light.

Check the voltage on CON1202 (LCD connector) in reference to ground, pins: 1, 3, 13, 15 and 17, during backlight strobes.

1 - 19.370V
3 - 19.360V
13 - Oscilation from 1.320V to 1.380V
15 - 3.330V
17 - 3.312V

Check voltage pin 7, 11 CON1202

Machine hat geschrieben:Check voltage pin 7, 11 CON1202

Pin 7 - 3.381V
Pin 11 - 3.711V

Thanks for all you attention but i dont know what is wrong. Can someone point a direction please?

w00dman hat geschrieben:Thanks for all you attention but i dont know what is wrong. Can someone point a direction please?

Take it easy. We must get some precise informations to give You the most accurate diagnosis.

Next steps:
- check the voltage on both pins of L1209 bead in reference to ground (during MB is switched on and backlight strobes).
- check the resistance of L1209 bead - switch off the MB and disconnect the power supply and battery before this step.

Vogelek23 hat geschrieben:

w00dman hat geschrieben:Thanks for all you attention but i dont know what is wrong. Can someone point a direction please?

Take it easy. We must get some precise informations to give You the most accurate diagnosis.

Next steps:
- check the voltage on both pins of L1209 bead in reference to ground (during MB is switched on and backlight strobes).
- check the resistance of L1209 bead - switch off the MB and disconnect the power supply and battery before this step.

Thanks a lot for your time spent with me.

The voltage on L1209 on both sides oscillate between 1.320V to 1.380V.
The resistance of L1209 is 0.2ohm.

Again thanks a lot

Can someone help please?

Please desolder L1209, then connect pin 13 and pin 15 of CN1202 together and check the backlight. If it works normally after above-mentioned operations, You must replace U0601 (northbridge).

Thank you. Problem solved but I still have a question if you dont mind.

This laptop is only for consulting motherboards datasheet and some research on internet. There's any problem leaving the jumper on 13 and 15 pin? What this pin's is for?
I've search and I think this is for bright pwm, so this function will be deactivated right? The LCD back light will be on Low or High power?

Sorry for all those questions.

Thanks again.

w00dman hat geschrieben:Problem solved

Problem not solved, but evaded only.

w00dman hat geschrieben:There's any problem leaving the jumper on 13 and 15 pin?

The risk, NB may go to worse failure in a further time.

w00dman hat geschrieben:What this pin's is for? I've search and I think this is for bright pwm, so this function will be deactivated right?

Yes, it's a PWM signal for brightness regulation, and it will be deactivated.

w00dman hat geschrieben:The LCD back light will be on Low or High power?

100% of brightness only, it can't be regulated or switched to any lower level, beyond switch-off state.