HP Pavillon x360 14-ba174nz no image no backlight, LCD_VCC low (2.25V)

[ajgae]

Hi everyone!

First post on here so do tell me if i'm doing anything wrong. I have a laptop that came in with a broken hinge, but a healthy LCD. We replaced the LCD rear cover and now we do not get an image on the LCD anymore, though we get one via HDMI. There is sadly no schematic or boardview available for this motherboard (Bucks U42 DIS 17817-1) as far as i can tell, but I was able to identify which of the important pins on the LCD eDP connector (30 pin 2 lane) correspond to which pins on the motherboard display connector (which is 40pin, 30 for LCD and 10 for camera/face rec etc) by checking for continuity. Incidentally, though the LCD/camera cable was exposed for some time due to the hinge issue (~1 month according to the user), all of the eDP pins that are not NC (not connected) seem to show continuity across the cable and show up somewhere on the motherboard connector, so I assume that is fine.

An interesting thing I've been able to notice is that without the LCD attached, the motherboard supplies 3.3V on LCD_VCC, whereas with the LCD attached, LCD_VCC drops to 2.25V. I also get 0V on all three of BL_EN, BL_PWM and HPD.

Does anyone have any idea what could be causing this issue? I assume the LCD is still good as it was working before we replaced the LCD rear cover. My other main suspect for now is the LCD/camera cable but as I said it doesn't seem to show any broken connections.

Thanks very much for any help!

[FriedFred]

Somewhere you must have around 20 Volts... Maybe there is a fuse blown now.

[ajgae]

No, I do get BL_PWR at 19V so that's alright. Backlight voltage is there but BL_EN and BL_PWN are at 0V so theres no backlight. There is no image either so its not a no backlight but image present problem.

[pc_okay]

Is the camera still Working?
you can check résistance to ground on bl-en and LCD_VCC With and without edp+ screen
Maybe edp wire câbles are shorted together.

You may test With another screen/edp câble too…

[pc_okay]

Just an update, one of my young guy at the shop bend me a pin in the video connector (motherboard side) just yesterday, so no display no backlight.
(For a hard drive replacement !!! why the f*** you plug out the lcd cable dude !!!!)
So check you lcd cable and inside the motherboard EDP connector...
Untwist the pin solve the problem.

[ajgae]

Is the camera still Working?

yep, i just checked and its working fine

you can check résistance to ground on bl-en and LCD_VCC With and without edp+ screen
Maybe edp wire câbles are shorted together. You may test With another screen/edp câble too…

I tried another eDP display, larger than the original but same 30pin connector, and I don't get an image nor a backlight either. I do get 3.0V on LCD_VCC with the other LCD tho, where I had 2.25V with the original. In terms of resistances I get the following values:

PIN	original LCD (Ohms)	other LCD (Ohms)	no LCD (Ohms)
LCD_VCC	145	122.4	300
BL_EN	74k	83k	101k
BL_PWM	231k	392k	3.5M
HPD	45k	100k	101k

[pc_okay]

Do you check inside motherboard edp connector with micrososcope to see if pins are not twisted?
I'll Check tomorrow my resistance to ground on mine on LCD_VCC. (Not the same motherboard but similar connector)

[ajgae]

thanks, i'll inspect the connectors in more detail tomorrow. I'm also going to try checking if any of the twisted pair data lines are shorted to any other lines on the LCD connector since it is still my main suspect.

[ajgae]

sadly, it seems there is no obvious short between the data lines and other lines. upon visual inspection, it also seems that there are no bent pins anywhere on the connectors / cable. does anyone else have any ideas?

[FriedFred]

I suggest to use another, external Monitor to check, whether the computer is able to present a picture at all. With HDMI.
Second, I woul try to force to switch-on the backlight, with a let's say 1kOhm resistor to 3.3V. You can try every pin on that connector, more than 3.3mA will not flow. Maybe you can force a reaction.