HP DAG7HAMB8F0 rev F NO IMAGE/NO BACKLIGHT internal display but works HDMI

[nicoar10]

Hello! In this case I have an HP with motherboard DAG7HAMB8F0 rev F. The laptop powers on and shows video on an external display, but not on the internal screen. There is no image / no backlight.

I have checked and I do have 3.3 V at the display connector. There is also no short circuit at the display connector. I have checked the 3 V and backlight fuses and they are OK.

What I can’t understand from this schematic is that I cannot find the backlight boost circuit. According to the schematic, this display works with the same VIN supply, which passes through a fuse and is then labeled “backlight.”

EDP LINES SHOW NORMAL VALUES TOO
I FOUND DIGITAL_CLK_L 0.073 SEEMS LOW with lcd connected. If disconnect up more than 0.400.

I test with know good LCD too.
Any help is welcome!

[Vusal]

Now, there's something else. If there's an image in the background on the panel and there's no backlighting, that's another issue.

If there's no image or light in the background, that's another issue.

1. If you only want to analyze the backlighting, the panel must have main voltage and LCD_VCC. For backlighting, you need to check VADJ and BLON. VADJ performs scanning, i.e., the pmm signal, while BLON is the enable signal.