Here’s a link to the [link|https://www.alisaler.com/hp-elitbook-840-g2-6050a2637901-mb-a02-schematic/|schematics] for the motherboard (I think, check the motherboard “board number” to verify).
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On p.44/77 you will find the EDP connector pinout. Pins 38-40 are the backlight power wires.
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On p.44/77 you will find the motherboard’s EDP cable connector pinout. Pins 38-40 are the backlight power wires.
If there is no power on these pins, you will have to check the PVBAT source to find out where it comes from.
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Also be aware that the “backlight enable” lead needs to have voltage on it to turn the power on and off ''in the panel.'' This voltage is controlled by the BIOS chip and by the lid switch sensor which is mostly found on the power button board so you may want to check that it is working OK as well. Not sure what this voltage is in your model. It depends on the design of the LCD panel. Some I’ve found in the past require a signal voltage of +3.3V to enable the backlights and of course 0V to disable
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Also be aware that the “backlight enable” lead (BLKT_EN) needs to have voltage on it to turn the power on and off ''in the panel.'' This voltage is controlled by the BIOS chip (L_BLKT_EN)and by the lid switch sensor (LID_SW#) which is mostly found on the power button board so you may want to check that it is working OK as well. Not sure what this voltage is in your model. It depends on the design of the LCD panel circuit by the panel maker. Some I’ve found in the past require a signal voltage of +3.3V to enable the backlights but others have been +5V and it requires 0V to disable.
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There should always be power on the video cable connector backlight power pins to the panel. It is turned on and off ''in the panel not on the motherboard'' by the backlight enable lead.
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There should ''always'' be power on the video cable connector backlight power pins to the panel. It is turned on and off ''in the panel, not on the motherboard'' by the backlight enable lead.
Here’s a link to the [https://www.alisaler.com/hp-elitbook-840-g2-6050a2637901-mb-a02-schematic/|schematics] for the motherboard (I think, check the motherboard “board number” to verify).
+
Here’s a link to the [link|https://www.alisaler.com/hp-elitbook-840-g2-6050a2637901-mb-a02-schematic/|schematics] for the motherboard (I think, check the motherboard “board number” to verify).
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On p.44/77 you will find the EDP pinout. Pins 38-40 are the backlight power wires.
+
On p.44/77 you will find the EDP connector pinout. Pins 38-40 are the backlight power wires.
-
You will have to check the PVBAT source to find out where it comes from.
+
If there is no power on these pins, you will have to check the PVBAT source to find out where it comes from.
-
Also be aware that the “backlight enable” leads needs to have voltage on it to turn the power on and off ''in the panel.'' This voltage is controlled in BIOS by the lid switch sensor which is mostly on the power button board so you may want to check that it is working OK as well.
+
Also be aware that the “backlight enable” lead needs to have voltage on it to turn the power on and off ''in the panel.'' This voltage is controlled by the BIOS chip and by the lid switch sensor which is mostly found on the power button board so you may want to check that it is working OK as well. Not sure what this voltage is in your model. It depends on the design of the LCD panel. Some I’ve found in the past require a signal voltage of +3.3V to enable the backlights and of course 0V to disable
-
There should always be power on the video cable pins to the panel. it is turned on and off in the panel not on the motherboard
+
There should always be power on the video cable connector backlight power pins to the panel. It is turned on and off ''in the panel not on the motherboard'' by the backlight enable lead.
Hi @thisisfine ,
Here’s a link to the [https://www.alisaler.com/hp-elitbook-840-g2-6050a2637901-mb-a02-schematic/|schematics] for the motherboard (I think, check the motherboard “board number” to verify).
On p.44/77 you will find the EDP pinout. Pins 38-40 are the backlight power wires.
You will have to check the PVBAT source to find out where it comes from.
Also be aware that the “backlight enable” leads needs to have voltage on it to turn the power on and off ''in the panel.'' This voltage is controlled in BIOS by the lid switch sensor which is mostly on the power button board so you may want to check that it is working OK as well.
There should always be power on the video cable pins to the panel. it is turned on and off in the panel not on the motherboard