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-   -   HP ZR2740w screen goes black (https://www.badcaps.net/forum/showthread.php?t=67050)

Greeneman42 01-16-2018 07:19 PM

HP ZR2740w screen goes black
 
3 Attachment(s)
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. I tested mine after reading advice of others having the same issue and mine along with 3 others in a line were bad. Iím wondering though, should I try and replace these with the same value resistors or will they go out again? Is there maybe a higher value I could use to help prevent the new ones burning out?

I donít know anything about circuit design but I can solder okay. I attached images of the problem resistors and a screenshot of the post because I canít find the thread for the life of me. Just looking for some advice, thanks!

Andrew F. Ali 01-17-2018 09:06 AM

Re: HP ZR2740w screen goes black
 
The post said 50Mohm 1000V resistors......What the hell is that? Resistors don't have voltage as a spec, they have power ratings in Watts. Anyway you must replace your bad resistors with the same value resistance. The power rating could be higher NOT lower. Those SMD resistors are 1/16 Watt. So perhaps if you can get it to fit 1/8 Watt will work. The key is 'same' resistance.

diif 01-17-2018 11:48 AM

Re: HP ZR2740w screen goes black
 
But yours turns on before going black ? Sounds like you have a different problem.
When you say black, do the backlights power off, or is it the screen going blank ?
I have a ZR2740W that had the same issue. I cured it with a reflow.

Greeneman42 01-17-2018 08:11 PM

Re: HP ZR2740w screen goes black
 
Quote:

Originally Posted by Andrew F. Ali (Post 797942)
The post said 50Mohm 1000V resistors......What the hell is that? Resistors don't have voltage as a spec, they have power ratings in Watts. Anyway you must replace your bad resistors with the same value resistance. The power rating could be higher NOT lower. Those SMD resistors are 1/16 Watt. So perhaps if you can get it to fit 1/8 Watt will work. The key is 'same' resistance.

My plan was to replace the four 500k resistors with two 1Mohm resistors. However I ordered 1W rated ones. Would that affect the resistance?

Quote:

Originally Posted by diif (Post 797962)
But yours turns on before going black ? Sounds like you have a different problem.
When you say black, do the backlights power off, or is it the screen going blank ?
I have a ZR2740W that had the same issue. I cured it with a reflow.

It works fine for a couple of minutes and then the picture stops moving and fades to black within about a second. It seems to work until it warms up because turning it off and on again wonít change anything until you let it sit for a while. Also it looks like the backlight is still on when it goes out.

diif 01-17-2018 09:54 PM

Re: HP ZR2740w screen goes black
 
Quote:

Originally Posted by Greeneman42 (Post 798054)
My plan was to replace the four 500k resistors with two 1Mohm resistors. However I ordered 1W rated ones. Would that affect the resistance?


It works fine for a couple of minutes and then the picture stops moving and fades to black within about a second. It seems to work until it warms up because turning it off and on again won’t change anything until you let it sit for a while. Also it looks like the backlight is still on when it goes out.

Yes, that sounds like the problem I had. Monitor turns on, works for a bit then goes black with the backlights on. Sometimes coming back on, to go to black again.
It was a BGA issue and not resistors.

What readings do you get on those 4 resistors ? 400k

The thread you couldn't find is here http://forum.eserviceinfo.com/viewto...hlight=zr2440w

Greeneman42 01-17-2018 10:27 PM

Re: HP ZR2740w screen goes black
 
No reading (infinite resistance). I even went around the board and tested others to make sure my multimeter was working and got normal readings on the others. All four in series (parallel?) were like this. Sorry, what do you mean BGA issue?

diif 01-17-2018 11:13 PM

Re: HP ZR2740w screen goes black
 
Quote:

Originally Posted by Greeneman42 (Post 798083)
No reading (infinite resistance). I even went around the board and tested others to make sure my multimeter was working and got normal readings on the others. All four in series (parallel?) were like this. Sorry, what do you mean BGA issue?

BGA is ball grid array. The way the main chip is soldered to the board.
Resistor R810 is marked 4493 which is 400 kohm, not 4.7 Mohm as described in that thread. Which also mentions no power. You have power.

Greeneman42 01-18-2018 10:43 AM

Quote:

Originally Posted by diif (Post 798089)
BGA is ball grid array. The way the main chip is soldered to the board.
Resistor R810 is marked 4493 which is 400 kohm, not 4.7 Mohm as described in that thread. Which also mentions no power. You have power.

So do you mean re-flowing the solder or re-attaching that chip? I have a heat gun but not a hot air gun if that's what it takes. I was given this monitor for free by a family member and am trying to give it some life back without investing too much into it.

I will try to take more pictures tonight and test the caps on the power board.

diif 01-18-2018 11:37 AM

Re: HP ZR2740w screen goes black
 
Yes, it's just melting the solder rather than removing the chip and replacing the balls.

Greeneman42 01-18-2018 01:08 PM

Re: HP ZR2740w screen goes black
 
So the issue is possibly a bad/intermittent connection beneath the main chip on the main board?

What about this process?
http://www.instructables.com/id/BGA-rework/

That makes more sense than the power board having issues since I seem to have power just fine. It is odd that those same four resistors were out on mine as in the other thread though.

Greeneman42 01-19-2018 08:50 AM

Re: HP ZR2740w screen goes black
 
Sorry to double post but I put it all back together and it worked fine for 20-30 minutes last night before I shut it down. :S

Edit: I also never mentioned this but the monitor was absolutely disgusting inside. There was a pile of roaches inside the back cover. I dumped all of them out and threw it in the sink and scrubbed it down. I also wiped down and cleaned the boards and the inside of the monitor with some wipes. I got it pretty clean and used Lysol for good measure where I could. Maybe cleaning out some of that filth helped

Snout 11-08-2019 10:12 AM

Re: HP ZR2740w screen goes black
 
Quote:

Originally Posted by Greeneman42 (Post 797842)
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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