HP Laptop not detecting internal screen (HP 15-cs0906nz)

[honestmstk]

Hello everyone, as mentioned in the title im having problems with the screen circuitry. When i got the laptop it had a burnt hole in its screen cable and a few broken wires. It displayed on an external monitor without issue, still does. I ordered a replacement cable and popped it in today but still nothing.

I then looked around on the board to see if theres a fuse that couldve blown and found one. Not entirely sure if its a fuse, i mean its white ( ill be attacing pictures), but it doesnt have continuity. I looked to see where the connection went and from the left side of the fuse it beeps on a few wires on the screen connector. It also seems to be a ground which makes little sense to me (the left pad on the fuse). The same pads on the lcd connector are still grounds even with the fuse broken. I also saw that the left pad of the fuse is connected to a three pad mosfet(?) above it. I tested the mosfet and its also showing weird behaviour, unlike the other ones on the board. I even tried replacing it and at first it tested differently and after turning on and off the laptop it started behaving like the previous one- the ground pad and the one next to it short. And thats where my ideas stop, what could be the fried component and why has the fuse allowed them to fail?

The board id is DA0G7BMB6D0 rev d and i was unable to find a boardview.

Many thanks in advance to the members of this amazing forum, even if we dont figure it out.

EDIT: Even if that is a fuse i dont think it has anything to do with the display connector, i could be wrong still. The fuse is shorted to ground on one side and has no voltage going through it on the other.

[Stevedb]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

Yes it is fuse . So you have short there that is why the fuse blown how much ohms resistance to ground do you have exact there.

[Stevedb]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

How much resistance do you have on +19v on the lcd connector.

[honestmstk]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

Around two ohms on the fuse. Can you tell me which pin is the 19 volt on the connector? Ill try my best to find it in the meantime. Thank you

[honestmstk]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

How much resistance do you have on +19v on the lcd connector.

I tried going from the right pad of the fuse (the side which is disconnected from everything and not a ground) to the pins of the lcd connector, and not a single beep. I thought the voltage pins would be connected to that, guess not.

[Stevedb]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

If you have a picture mostly it is the big track that goes to three or 4 pins. By the way if you have a short to if you disconnect the screen?

[honestmstk]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

If you have a picture mostly it is the big track that goes to three or 4 pins. By the way if you have a short to if you disconnect the screen?

Its kind of blocked by the ram slot so i dont see which track it is, but i measured all of them

4 or 5 are measuring 1ohm
2 are measuring 46 ohms (not next to each other)
rest are open line

[honestmstk]

HP Laptop not detecting internal screen (HP 15-cs0906nz)

So this is a continuation of this tread: https://www.badcaps.net/forum/showthread.php?t=106465, since it went cold i cant expect any help there.

TLDR: The laptop model from the title works on external display, doesnt display to an internal one, i found new clues.

The white thing i thought was the backlight fuse isnt that 100%, tested on another similar laptop which has a working screen and it measures the same behaviour. Its to do with one of the ports.

Other thing i found are 5 capacitors which are shorting to ground on both sides right next to the LCD connector, not like false beeps on the multimeter, full on 1 ohm short. And the only thing nearby is a 5 legged chip with the marking L2A4. I couldnt find the pinout for it. On the side with 3 legs, 2 are shorting to ground, other legs are not. Is this normal for a L2A4 chip?

I will attach a picture of the 5 capacitors and the chip. Hopefully you can help me figure this out. Thanks in advance.

[honestmstk]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

Update: i fixed the problem.

So if anyone from the future sees this, it was the 5 pin L2A4 mosfet. It shouldnt be shorted to ground on any pins other than the middle one of the 3. I didnt have an exact one, but used one from a 2010 macbook air motherboard. The thing that gave me confidence was the fact that it was right next to the lcd connector- so it served the same purpose as mine. And im really bad at understanding datasheets for the various chips.

[mon2]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

Well done! Thanks for updating the thread.

[honestmstk]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

Thank you, really proud of myself for managing it, especially after a repair shop held the laptop for 2-3 weeks and didnt even try to diagnose by the look of things.

[Stevedb]

Re: HP Laptop not detecting internal screen (HP 15-cs0906nz)

Good work man , congratulations