Yesterday there are a Nokia 3110c comes in a state of complete darkness.
LCD and keypad lights do not glow. The owner said, his mobilephone fell into the water.
Hemmhh .... Water damage. Usually rusty. Or shorting.
Open the cashing and strip that mobilephone. See the engine board. But there's no rust and not short-circuit (shorting) too. There's only a little mushroom. Clean it using thinner. And start measuring the voltage that should exist so that the display light and keypad lights up. Look at the scheme, the voltage for the LCD and keypad lights should come out of capacitor C2315 (VLEDOUT1). But that measured only 3.8 volts, the same as VBatt (properly, the voltage was about 12 Volt).
This is likely because the lights IC not working. But that does not mean that the broken part is the lights IC. It may be that the IC sulking because he did not get the required supply voltage. Check the voltage for N2301 from capacitor C2314 and L2305. As a result, 3.8 Volt. Means the voltage has been entered into N2301 perfectly. Then why the screen and keypad still dark?
Do not forget to measure also point EN (Enable / PWMTahvo) of 1.8 volts at the point of J2316. And in fact exist. But why the LED's was still dark as well??
The first step, replace the LED driver (N2301). You see, the requirement for the lights IC to work is all OK, but she still did not work. Maybe, this led driver is damaged. Just Replace. Take scraped from the broken board engine of Nokia 5300.
And, after replacement, was still too dark ....
The output voltage at c2315 still 3.8 volts !!
Also try changing the capasitor C2315. Could be, N2301 already issued a voltage very well, but the C2315 can not be running it perfectly (water damage, maybe this capacitor is leaking).
Fetch also from the carcass that was Nokia 5300. Put it.
Wait a moment let cool (still HOT, finished in-blower).
And ........ Taraaaaaaaaa. SUCCESS!
Done ...!! Problem solved.