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Revealed in January 2021 and released in March 2021, the HP EliteBook 840 Aero G8 is a lightweight version of HP's EliteBook 840 G8.

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Bildschirmhelligkeit ist zu gering

Hallo,

ich habe ein gebrauchtes Elitebook 840 G8 gekauft und habe den Eindruck, dass das Display zu Dunkel ist. Ich habe schon das Display durch ein äquivalentes Display ausgetauscht, allerdings erscheint es mir immer noch zu dunkel.


Anzeigegerät

14" diagonal, FHD (1920 x 1080), IPS, anti-glare, 1000 nits, 72% NTSC, HP Sure View Reflect integrated privacy screen Entspiegeltes FHD-Display (1920 x 1080) mit 35,6 cm (14 Zoll) Diagonale, IPS, 1000 Nits, 72 % NTSC, integrierter HP Sure View Reflect-Blickschutz [16,17,18]

Kann es eventuell am Bildschrimkabel zum Mainboard liegen oder am Mainboard selbst? Hat jemand Tipps oder Ratschläge?

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Hello,

I bought a second-hand Elitebook 840 G8 and have the impression that the display is too dark. I have already replaced the display with an equivalent display, but it still seems too dark to me.

Display device

14" diagonal, FHD (1920 x 1080), IPS, anti-glare, 1000 nits, 72% NTSC, HP Sure View Reflect integrated privacy screen Anti-glare FHD display (1920 x 1080) with 35.6 cm (14 inch) diagonal, IPS, 1000 nits, 72% NTSC, integrated HP Sure View Reflect privacy screen [16,17,18]

Could it be the screen cable to the mainboard or the mainboard itself? Does anyone have any tips or advice?

Translated with DeepL.com (free version)

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@oldturkey03 : Any idea how to tackle this issue?

von

@benz78 fingerscrossed that we can figure this out. My money is on the boost circuit or the display. Unless there is an issue with corrosion etc. Then everything goes.

von

I already changed the display. So maybe its the boost circuit?

This sounds already more complicated but I would give a try :) Happy to learn more about it

von

I also realised that even when the laptop is turned of and no AC is plugged in there is a very high frequent sound comeing from the back of the computer. Is this related to the boost circuit?

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@benz78 @bluecorn how dark is dark? It could be an issue with the backlight driver, boost circuit or the actual backlights. For now, measuring the voltages on the backlight output should help to make a determination where it originates from. It will help if you can give us the model for the motherboard. It might be printed on the side that faces the keyboard. Now, to work on the computer, use this HP EliteBook 840 Aero G8 Maintenance And Service Guide. Once we know what motherboard it has, we "might" have the right schematic.

Translation

@benz78 @bluecorn wie dunkel ist dunkel? Es könnte ein Problem mit dem Hintergrundbeleuchtungstreiber, dem Boost-Schaltkreis oder der eigentlichen Hintergrundbeleuchtung sein. Die Messung der Spannungen am Ausgang der Hintergrundbeleuchtung sollte helfen herauszufinden, woher das Problem kommt. Es wäre hilfreich, wenn Du uns das Modell der Hauptplatine nennen könntest. Es könnte auf der Seite, die der Tastatur zugewandt ist, aufgedruckt sein. Verwende dieses HP EliteBook 840 Aero G8 Maintenance And Service Guide, um an dem Computer zu arbeiten. Es ist zwar auf Englisch verfasst, aber ich hoffe, er ist dennoch nützlich für dich ist. Wenn wir wissen, welche Hauptplatine er hat, können wir "vielleicht" den richtigen Schaltplan finden.

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I tried to measure the brightness with an app called "Photometer Pro". It showed around 100 Lux. In comparission my Xiaomi Notebook Air 2017 showed a value of around 200 Lux. Both devices on maximum brigthness in the seetings.

I installed an official HP Support App to determinen all drivers. Not sure if it covered also the driver for the backlight. Or if there is anything else to consider.

tear down of the computer I maybe will do it on the weekend.

I just checked the SN of the computer and the HP Website and it showed me some specification of the laptop:

"Intel® Core™ i5-1145G7 (2,6 GHz Basisfrequenz, bis zu 4,4 GHz mit Intel® Turbo Boost-Technologie, 8 MB L3-Cache, 4 Cores, 8 Threads)"

And according to the manual you attached it says that the system board is:

M56137-xx1 --- for Intel Core i5-1145G7

or

M56138-xx1 --- for Intel Core i5-1145G7 (OSR)

And how do I measure the voltages on the backlight output ?

von

I also realised that even when the laptop is turned of and no AC is plugged in there is a very high frequent sound comeing from the back of the computer. Is this related to the boost circuit or mainboard?

von

@bluecorn it could be, but it could also just be a "normal" coil whine coming from the battery circuit. I'll check and see if I have a schematic for your board. It may just help to determine where and what regulates your backlight.

von

@oldturkey03

Do you already had the chance to look for the schematic of the system board? It would be greatly appreciated as I'm planning to attend a repair cafe next week and seeking assistance. Having the schematic plan of the main board would prove immensely helpful.

von

@bluecorn it's a beast to find anything for:-) I do have have some schematics but not sure if they apply for your board as well. We really would need to see more of your board to check it out. It look like pin 13 on your display connector is part of the brightness. See what the voltage is on that. Careful, use a very fine probe so you do not shorten out the pin.

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I will give an other try to see if the lcd cable is really fixed on the Mainboard. I saw a YouTube tutorial of an older generation where the guy tried to fix it that way

[Edit by mod:]

Ich werde einen weiteren Versuch unternehmen, um zu sehen, ob das LCD-Kabel wirklich auf dem Mainboard befestigt ist. Ich habe ein YouTube-Tutorial einer älteren Generation gesehen, in dem der Typ versucht hat, es auf diese Weise zu reparieren

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bluecorn wird auf ewig dankbar sein.
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