Lenovo Y50-70 (not touch) - Screen LED Backlight

[Kashi1712]

Hi all,

I need a little help with my second Lenovo y50. Board schematic is attached.

Little explanation, the 40 pin connector for the LCD was broken, I made the replacement and it looks fine. I can see the screen showing some images.

Problem here is that the screen backlight doesn't turn on (tried also the FN + ...). Screen is working fine on my other y50 laptop (cable also).

Could you help me to identify what is wrong on the board? I think about something wrong with pin 28 of the LCD connector but that it...

Thanks a lot !

[piernov]

Please post a picture of the area you worked on.
Also, what voltage do you get on pin 28, 29 and 40 of LCD connector?

[Kashi1712]

Hello Piernov,

Thanks for the answer, here is the picture.

Regarding voltage, i get 0V for the 3 pins (28 -29 -40)

Thanks !

[rookieme]

There you should have 19V in order to get backlight.
Check R375 and measure voltage at both sides at R375.
R375 is 0 ohms and acts as a fuse.
If it is burned no voltage could pass through to drive the backlight.

[piernov]

Not so pretty but it should do the job. Not sure about the 4th and 5th pins from the left though.

Could you mesure all the voltages on PU1203 pins?

[Kashi1712]

The 4th and the 5th from the left, there was a scratch, I verified, and both pin join to the ground, so it should be fine.

To solder the connector, I've used my smd rework station with soldering paste, as this is really small, it is really difficult to make it really clean.

I'll measure voltage right now ! Thanks !

[Kashi1712]

Is that normal that there is no chip on the pu1203? I will do measures tomorrow as it is quite difficult to access (under the heatsink)

[rookieme]

yes it's normal, you get 19V via R375, R205 doesn't exist [it has @ sign] and schematic has is as it's an option but not used
[pu1203 is a boost converter for 12V]

[Kashi1712]

Ok, so the pu1203 has 12 pins

1 - 0v
2 - 0v
3 - 0v
4 - 5.17v
5 - 0v
6 - 0v
7 - 0v
8 - 0v
9 - 0v
10 - 0v
11 - 0v
12 - 0v

This 5v is strange.. sometimes it drops to 3.5v and then go back to 5.17v...

[Kashi1712]

Originally Posted by Kashi1712

Ok, so the pu1203 has 12 pins

1 - 0v
2 - 0v
3 - 0v
4 - 5.17v
5 - 0v
6 - 0v
7 - 0v
8 - 0v
9 - 0v
10 - 0v
11 - 0v
12 - 0v

This 5v is strange.. sometimes it drops to 3.5v and then go back to 5.17v...

From the schematic, I think pins are not really the same... I guess that the 4th pin is actually pin 8 (so the 5v input is correct)

[rookieme]

have you measured voltage at R375 ?

[Kashi1712]

I've tried to find that one, but don't know where it is located on the board. Any clue?

[rookieme]

you can follow the trace from the pins of the lvds if that is possible
a boardview can help you to find it at the moment if you can find one for this board

[Kashi1712]

Didn't find the boardview, I will check if it is visible or not.... Looks difficult

[rookieme]

Last option is to run a cable from 19V [B+ or CPU_B+ or anything that suits for you] and solder it at lvds pins 38-40.
A better option is to use a zero ohm resistor as a fuse or a use of 2,5- 3A between the cable and the pins.
With the 19V you'll get your backlight.

[Kashi1712]

the 19v wire is not too risky? I can see on the schematic that there a some resistor/capa.

I would not take the risk to damage the LCD that is working... But if I can rewire 38-40 pin in another way that is not risky, i'm ok with that.

[piernov]

R375 should be the component circled in red in the following picture. Maybe yours is blown too.

(Source: http://www.elektroda.pl/rtvforum/topic3228153.html )

[rookieme]

nice photo, this should do the job

[Kashi1712]

Ok from the point next to pu1101, I get 7.8v. on the other one, 1.30v

I've tried to put 19v from the 16th pin on the pu1101 but laptop shuts down immediately. Still doesn't work

[Kashi1712]

I will post a picture of it, mine looks just fine