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Old 11-08-2019, 10:12 AM   #12
Snout
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Join Date: Jul 2017
City & State: Broby
My Country: Sweden
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Default Re: HP ZR2740w screen goes black

Quote:
Originally Posted by Greeneman42 View Post
Hi, I recently got a monitor that goes to a black screen after about two minutes. The backlight will remain on though. After some googling, I think the problem is resistor R810.
On mine, R810 was fine (showed about 350-400k and it's supposed to be 500k (edit: measuring while they were still on the board, which will skew the readings, but they were not shorted nor open) ) - also caution, those four resistors next to each other are _not_ in series! The first pair has one common pole, then both go separate ways. And the other pair likewise has one common pole, but the other ends don't go the same way, so I wouldn't just solder together the endpoints with one or two resistors.

Since I definitely can't reflow or rework a BGA, my fix for now has been to plug in two 12cm wide fans (quiet ones!) over the control board and power board, and am now running a test to see if it will run for hours without developing the 'freeze screen and fade to black, while backlight is on'.

Troubleshooting tips:
Lifting pins 2 and 3 on the big connector to 5V through one 820ohm resistor each did indeed turn on the backlight and forced power on, so the fans spun up. After a couple tries, I got the 'some weird sh-t is happening, gonna show the red-green-blue-white-black test pattern' going.

Before that, _nothing_ would turn the monitor on! I tried with laptops and a raspi, through HDMI-to-DVI and HDMI-to-Displayport, but got no image. What finally got the control board to acknowledge a signal was using a previous laptop that has Displayport out and was used with it, so it's straight DP-to-DP.

With the multitude of adapters I tried at first, and nothing worked, I thought something must have died since -some- combination ought to work for a machine that doesn't have dual-DVI or DP out... but nope. A straight DP-to-DP did it, and I could snip off the pull-up resistors, the screen kept running fine.

I'm just leaving it on now on the side, showing an aquarium screensaver, so I can easily do other things while keeping an eye on it to see if it 'freezes up' again.

(Possibly just a fan over the control board would be enough, if it indeed does work, but I figured, why not.. They're low power, and steals 12V from the red and black lines on the PSU-to-Control connector.)
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