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Old 07-16-2017, 03:04 PM   #81
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Default Re: HP ZR2740w almost dead

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Originally Posted by wash View Post
vo1 30
vo2 30
vo3 30
vo4 60
vo5 30
vo6 30

and all of them slowly drops....
(when i say 30, in fact it's around 28-29)
Wow. I have the exact same measurements! And they're negative, too (ie, with the multimeter black connected to monitor GND, the voltages show as -30 and -60 and 'rising' up towards zero, not positive values as one would expect.)

In my case also it's Vo4 that bumps to -60 after the first 'flash', and all others are at -30, then dropping off as the light's off. (Capacitors discharging when 'idle', I suppose.)

Have to peek around this thread now for hints, such as forcing BL_ON. Did you solve your problem by the way, seeing how we have the same backlight-pin readings?
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Old 07-16-2017, 03:08 PM   #82
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Default Re: HP ZR2740w almost dead

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Originally Posted by cmg View Post
OK i got it done and am posting a little more info in case anyone else has the misfortune to try to fix one of these panels. I wouldn't bother unless you are already very experienced at fixing such devices to component level. This panel was not designed with servicing in mind!!

Here are the important steps
- to diagnose if the LED strips are faulty easily, insert a piece of solid core wire as an extension to your multimeter in order to check the voltages on the connector feeding the LED strip. This can be done without disassembling the chassis at all. If any one of these rises much above 30V then there is an open circuit. Mine went to about 60V. Proceed to repair the panel.
- take note if the open circuit is on the left and/or right side LED strip
- remove chassis taking care with plug to LCD panel
- unplug the LED driver cable at the chassis end. DO NOT ATTEMPT TO UNPLUG THE OTHER ENDS.
- lay panel face down
- remove metal shield to TCON PCBs but do not remove PCBs
- unclip the panel from the steel frame.
- undo the 6 screws from the 2 part plastic frame
- prise apart the plastic frame at the edge with the LEDs (bottom edge)
- carefully hinge the panel open
- remove the small screw on the white plastic 'light guide'. This is in the corner, inside the panel
- with the panel closed again, remove the shiny black tape
- push forward a couple of the white plastic clips found underneath this. Every one i did broke off...
- unscrew the many tiny screws holding the LED strip, from inside the panel.
- try to pull the white plastic light guide away from the edge of the panel and ease out the LEDs. There are 2 metal pins protruding from the case which also anchor the strip - you need to pull it about 1-2mm away to clear these. Try not to force it... each time i did it, i knocked the top off one or more LEDs creating more work...
- fix the PCB. May well just be the connector.
- test the strip using a constant current PSU before reassembling. Set to approx 100ma limit, 30V. The connector on the PCB is really poor and will need retouching. Test from the chassis plug to make sure this connector is checked.
Nice guide! I might try putting together a 30V LED-strip externally first and connecting it instead of the one Vo4 goes to, just to see if it lights up as it should, before taking the whole thing apart.. I know from earlier monitors that, at least with the tiniest bit of unstable hands, it's pure hell to piece all the layers back together again. >.<
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Old 07-16-2017, 03:13 PM   #83
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Default Re: HP ZR2740w almost dead

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Originally Posted by cmg View Post
- test the strip using a constant current PSU before reassembling. Set to approx 100ma limit, 30V. The connector on the PCB is really poor and will need retouching. Test from the chassis plug to make sure this connector is checked.
A sort-of related question: If not having a current-limited lab supply, but checking with 'just any 30V source', what type of resistor should I put in series with the LED strip I'm checking, to keep the current down (but not so low as to not light up at all)? Do I need a big power resistor to eat up current, or will just any resistor with the right ohm value do?
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Old 07-16-2017, 05:27 PM   #84
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Default Re: HP ZR2740w almost dead

Hi Snout.

OK, well i bet your problem is the same. Yes, I did fix it by replacing the LED(s). My instructions you quoted show you how to take it apart and get to the LED strip.

One test you can do is to put a resistor over the VO4 strip and check the monitor comes on. I did this.. can't recall the current you need (hence resistor value). This needs to be a 10W resistor. However, the diagnosis is clear so you dont really need to bother.

Replacing the LEDs on the strip is not impossible but very tough unless you are very used to hot air soldering/desoldering. The LEDs are tiny and easily melted by the hot air. Because the pads are underneath the LEDs you have to solder them with hot air. The strip itself is a heatsink which makes this even harder as it spreads the heat. I damaged a few LEDs trying to do this and made a bit of a mess of the first ones i did. I've seen the videos of people doing this by heating the underside of the strip for TV backlights but i very much doubt this is possible here. The LEDs are closely spaced so you'd end up moving the other LEDs.

You need to get the exact same LED as it appears to be unique...
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Old 07-16-2017, 06:08 PM   #85
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Default Re: HP ZR2740w almost dead

I find resting the led strip on a hotplate is easier and cleaner than using hot air. Less chance of burning/melting and it leaves both hands free.
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Old 07-17-2017, 02:28 AM   #86
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Default Re: HP ZR2740w almost dead

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Originally Posted by cmg View Post
You need to get the exact same LED as it appears to be unique...
Ouch, what a horror! And since it's inside the monitor itself, I bet buying a replacement strip would be just about impossible. Well, nothing for it but open and have a look, and pray it's just a bad connector that needs fixing!

Thanks for your tips!
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Old 07-17-2017, 02:52 PM   #87
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Default Re: HP ZR2740w almost dead

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.. pray it's just a bad connector that needs fixing!
Yes, that is also quite likely. The connector they put on is rubbish. On the 1st one i fixed the original fault was a dry joint on this, but then i cracked the top off a few LEDs trying to remove the LED strip.

Make sure you do this "- push forward a couple of the white plastic clips found underneath this. Every one i did broke off..." and remove the strip without force. Don't take out the screws before doing the above step. Refer to the disassembly doc too. Also don't remove the connector early on- this will cause it to rip off the PCB. I can't remember if you have to remove it to get the strip out or not.

It is quite a fiddle to resolder the connector, i used hot air for that as well, then retouched it with the iron.

I noticed that if you test the LEDs with a meter on diode test you will see them light up faintly. This way you can easily see which ones are working. They can fail s/c which can still work or o/c which causes what you have - or it can be the connector.

Note that the strip is wired as an alternating set of 3, i.e. 1, 2, 3, 1, 2, 3, .. This is marked on the PCB. You know you are looking for VO4, so follow which set that is. I scoured the web to find a replacement strip to no avail.

To: 'diif'
Quote:
I find .. hotplate is easier .. than using hot air.
I get it in general, but I will "eat my hat" if I hear of anyone successfully repairing this strip using this method. I managed to do it OK with hot air in the end but wasted almost 50% of the new LED chips I had in the process.
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Old 07-17-2017, 03:31 PM   #88
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Default Re: HP ZR2740w almost dead

This was a while ago.. I just remembered I put more info on the repair here:

http://www.badcaps.net/forum/showthr...118#post758118

Btw, if anyone has one of these for parts, I'd like to buy the logic board as I have one which I think will be too much fiddle to fix.
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Old 07-17-2017, 06:21 PM   #89
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Default Re: HP ZR2740w almost dead

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Originally Posted by Snout View Post
Ouch, what a horror! And since it's inside the monitor itself, I bet buying a replacement strip would be just about impossible. Well, nothing for it but open and have a look, and pray it's just a bad connector that needs fixing!

Thanks for your tips!
There was some strange glitch in the Vo4 line of LEDs. When opening the monitor up and checking each LED one by one with a multimeter, they all worked, and were all connected in a string. Of course the error hides when it's about to be spotted.. *snerk*

This may be more of a software question, just in case someone with this monitor has had the problem - the darn thing now seems to work in Windows (Win7) at a nice 2540x1440 through DisplayPort, giving picture; when I switch to the other source, an Ubuntu via a DVI cable, I get the two choices 2540x1440 which turns the screen blank (backlight on, but all black) or 1280x720, which works. Does this just mean I need to get me a DVI-D cable or perhaps a HDMI-to-DVI adapter (the monitor only has DVI and DP in) for the bandwidth needed to display this higher resolution?
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Old 07-18-2017, 01:07 AM   #90
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Default Re: HP ZR2740w almost dead

OK, there's good news and bad news for you:

Good news:
- that problem is almost definitely the connector. You caught it open circuit once, but now its working. This means you don't need to find the LEDs and you don't face the problem of soldering them
- you almost have a nice working monitor!

Bad news:
- even fixing the connector is tricky. You will be able to do it with an iron rather than hot air but it is an SMD part with a small pitch; you need to have a good fine iron and be good at soldering. I think i posted pics of it.
- it is easy to rip the connector off the board completely when disassembling, making it harder to fix
- it only works on 1440p & VGA. You need DVI dual link cables for 1440p and thus it won't work via an HDMI adaptor - you need DVI or DP on your graphics card.

Good luck!
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Old 07-18-2017, 10:58 AM   #91
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Default Re: HP ZR2740w almost dead

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Originally Posted by cmg View Post
OK, there's good news and bad news for you:

Good news:
- that problem is almost definitely the connector. You caught it open circuit once, but now its working. This means you don't need to find the LEDs and you don't face the problem of soldering them
- you almost have a nice working monitor!

Bad news:
- even fixing the connector is tricky. You will be able to do it with an iron rather than hot air but it is an SMD part with a small pitch; you need to have a good fine iron and be good at soldering. I think i posted pics of it.
- it is easy to rip the connector off the board completely when disassembling, making it harder to fix
- it only works on 1440p & VGA. You need DVI dual link cables for 1440p and thus it won't work via an HDMI adaptor - you need DVI or DP on your graphics card.

Good luck!
Quite right - with a fresh bought DVI-D cable (at first I tried with what I had at home - a HDMI cable with a passive DVI-D adapter in each end ;P ) I now have a working monitor, with 2560x1440 on both DVI and DP inputs. Phew!

Well, it's been fun fixing up a large LED-strip monitor! My experiences so far have been with CCFLs only, tht electronics and tubes, and with 'single strip' smaller screens, such as laptops, where replacing the strip is as easy as cutting a length of a 5m spool of Generic Chinese White LED.

++knowledge; // for the win.
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Old 07-18-2017, 01:05 PM   #92
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Default Re: HP ZR2740w almost dead

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Originally Posted by cmg View Post
To: 'diif'

I get it in general, but I will "eat my hat" if I hear of anyone successfully repairing this strip using this method. I managed to do it OK with hot air in the end but wasted almost 50% of the new LED chips I had in the process.
Do I get to pick the hat ?
I've repaired LEDs using hot air and the hotplate. The hot plate gives much cleaner results with much less chance of burning the board or LEDs.
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Old 07-19-2017, 01:44 AM   #93
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Default Re: HP ZR2740w almost dead

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Originally Posted by diif View Post
Do I get to pick the hat ?
I've repaired LEDs using hot air and the hotplate. The hot plate gives much cleaner results with much less chance of burning the board or LEDs.
One thought, that wasn't used this time though, is that when it comes to that tiny, finicky connector between strip and cable, perhaps squirting in a little conductive (silver) glue might do the trick?
That's definitely for the more steady of hand than I. I'd get that little blob all over the place..
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Old 07-19-2017, 03:01 AM   #94
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Default Re: HP ZR2740w almost dead

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Originally Posted by Snout View Post
One thought, that wasn't used this time though, is that when it comes to that tiny, finicky connector between strip and cable, perhaps squirting in a little conductive (silver) glue might do the trick?
That's definitely for the more steady of hand than I. I'd get that little blob all over the place..
I've used solder paste in the past and hot air too attach micro USB connectors.
It can be a little tricky getting the correct amount out though. I find using my iron easier.
I do work looking through a stereo microscope, so I find this sort of work easy. Try resting your hand on your workbench to improve the steadiness.
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Old Yesterday, 08:23 AM   #95
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Default Re: HP ZR2740w almost dead

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Originally Posted by diif View Post
I've used solder paste in the past and hot air too attach micro USB connectors.
It can be a little tricky getting the correct amount out though. I find using my iron easier.
I do work looking through a stereo microscope, so I find this sort of work easy. Try resting your hand on your workbench to improve the steadiness.
Yep, when doing finicky work, like soldering, I have a steady-mounted 'helping hand' grip holding the details, and -being nearsighted- sit fairly closely leaned down without glasses to get a sharper image than a magnifying glass would get me. I'm good enough for thru-mount soldering, and relatively large things like big SMD details, but where it's small _and_ close by, about a micro-USB is the smallest I might (with luck) manage. Oh, the woes of being old.. that is, above fifteen or so.
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