HP ZR2740w almost dead

[Snout]

Re: HP ZR2740w almost dead

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?

[cmg]

Re: HP ZR2740w almost dead

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

https://www.badcaps.net/forum/showth...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.

[cmg]

Re: HP ZR2740w almost dead

.. 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'

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.

[Snout]

Re: HP ZR2740w almost dead

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!

[diif]

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.

[cmg]

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...

[Snout]

Re: HP ZR2740w almost dead

- 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?

[Snout]

Re: HP ZR2740w almost dead

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. >.<

[Snout]

Re: HP ZR2740w almost dead

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?

[cmg]

Re: HP ZR2740w almost dead

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.

[cmg]

Re: HP ZR2740w almost dead

OK well I now realize the LEDs may be unique to certain panels. These ones are also effectively on a heatsink with a 3rd pad which makes them difficult to get off the PCB as the heat is dissipated. Its not possible to hand solder - see the large pad underneath which is not reachable. It took me quite a long time to get this LED off with a rework station @ 350C. See the PCB is burnt now. Hopefully I can get better at this and solder replacements without damaging them.

[cmg]

Re: HP ZR2740w almost dead

Thanks for the soldering tips. I'm very experienced with through-hole but not much with SMD. I am fairly confident I'll work that out.

However, I'm still drawing a blank trying to find a suitable LED. The dimension seems uncommon and also all the LEDs seem to be flat in profile rather than having the domed lens that these have. I don't know how much difference that will make. I will add to my other thread regarding finding the parts.

I'm also wondering how it will work if i put a new LED which is undoubtedly higher efficiency in series with the old ones as it will be brighter. I suppose i may have to add a resistor in parallel with the new one(s)...

What a pain!!

cheers

[Hot_Dog]

Re: HP ZR2740w almost dead

You can try desolder LEDs with heat gun if you posses one, temperature like 400°C or so, carefully, not to burn pcb, try it first on some piece of solder somewhere else, then apply same procedure to the LED stripe... You are aiming for something like 20 - 40 seconds of applying heat until solder melts, thats relatively safe technique. For soldering new LEDs, common soldering station, flux and skilful hand is all you need...

You can try find similar diodes on farnell.com, even from your country:-)

Good luck with further repair...

[cmg]

Re: HP ZR2740w almost dead

Hi Hot_Dog. Great to hear from you. Thanks for replying.

Thanks very much for the advice about the dust. I am using the manual that you referred to. So now I have proceeded... I have avoided step 10-13, so kept all of the layers together. Hopefully this will avoid the dust problems.

The trouble with the guide is that it is for recycling the parts so they don't care about damage or reassembly. I hinged the panel back open so that I could access the LED strip but I couldn't get it out after taking out the screws. Then i saw step 17-19 where they take out the "light guide". Unfortunately as I had already loosened the LED bar, when i pulled out the white plastic light guide it has damaged 4 of the LEDs Also the connector ripped off the PCB. See attached (ruler shown for scale).

I have checked all the diodes with a DMM. All of them glow (even the damaged ones) apart from one which has a very low forward voltage and is not in the VO_6 section that had failed. So, i reckon the fault was exactly the same as yours - that stupid little connector had dry joints and is just too flimsy.

So now... I need to replace 5 LEDs and reattach the connector. The first problem is I need to get replacement LEDs, or the whole LED bar. I can't find where... Second is that i think this all needs to be done with a hot air reflow station which I don't have.

I think i'll start a separate thread on fixing LED strips as it's not specific to this monitor.

If anyone has any advice on finding replacement LEDs would be well received! (this is an LG panel).

Cheers

[Hot_Dog]

Re: HP ZR2740w almost dead

Hi, you are lucky, i checked spam in my mail, which i dont do often, and there was notification on this forum, which i didnt visit since succesfull repair:-) Acording to disassembly, i did it year and half ago and dont remember much. Since then, monitor works like a charm... I dont know, what are your technical skills, with mine, that was definitely doable, not even hard i would say (time consuming ofcourse), but im hardware/firmware developer of medicine devices, so...

Are you using this manual?



As your are on step 4, you are probably trying to remove PCB, make sure you unscrew all possible screws, disconect both flex cables and probably use reasonable amount of force, i dont realy remember, but there may be both sided tape, which hold pcb on the metal cover, but realy dont remember, so be careful not to broke PCB...

One hint for future assembly, you probably dont have non-dust enviroment, so when you will assembly, every piece of dust will be visible between LCD layers, and there will be a lot of dust, i did this mistake also, so i had to disassembly again and use a lot of compressed air during assembly every layer to be sure no visible piece of dust remain between layers.

I will check this forum for a while, if you will need some further advice, but as i said, dont remember details and will not disassembly mine again while functional...

[cmg]

Re: HP ZR2740w almost dead

Hi. I'd like to revive this thread as I have the same problem as Wash and Darkdead. From the information on this excellent forum I've managed to get to this point without trouble, but I would be grateful for further advice.

Specifically I would appreciate any advice on disassembling the LCD panel to get to the LED strips. I see at least Hot_Dog successfully managed this! I have the HP disassembly guide but I'm only at step 3 so far. It seems very delicate and also heavy - not a good combination!

I don't see how steps 4-9 work, and I'm not sure if i really need to completely disassemble the panel (i.e. to step 22) in order to remove one of the strips (VO6 was the failed one on mine).

Also, does anyone know where to source replacement SMD LEDs for this from and/or what parts they are exactly? I found a couple of ads for similar on eBay.

Thanks very much!

CMG

Here is what i did so far:

1. Observed that the behaviour of the monitor is the same as many others in that the monitor will not display an image and go into standby.
   
2. I noticed that the logic circuits have power. The front panel LEDs (blue/amber) lit and if i plugged in a device into the USB i could see it was powered up. Also the PC recognized the monitor model and resolution.
   
3. Next i checked the output of the PFC boost converter. This was 320V rising to 400V but then after a few seconds after power-up, dropping back to 320V. This matches BudM's explanation of the fault condition.
   
4. Then i checked the LED driver outputs. All of these were 30V when the boost converted was fired up, except one which went up to 60V.
   
5. I proved to myself that the problem was this output being O/C by soldering a 100R resistor from this LED driver output to ground, then the monitor worked! (note a 10W resistor is required otherwise the resistor will burn).

Note that to get to this stage I did not need to remove the PSU PCB from the chassis and would suggest others also do not, for safety. In fact, I could have checked the LED driver output first by poking the connector from the outside of the chassis. I'm scared by others' posts showing this 400V non-isolated circuit loose on the floor. You only need to trip or pull one of the cables and ZAP

[budm]

Re: HP ZR2740w almost dead

So when it LED goes to amber, do you still have running PC supplying the Video signal top the monitor?
The power supply section is always on unless the hard power switch in the back is turned off.
From user manual: Page 26, 27
Pressing the Power button, , puts the monitor in low power mode. (To turn power off completely,
use the switch on the rear of the panel.) The monitor also enters low-power mode when there is no
video signal input.
When the monitor is first powered on, the LED turns blue and remains blue for about half a minute. It
then turns off. If the monitor receives a signal outside its range (e.g., too high a frequency), the LED
flashes blue continuously.
This model does not use an OSD or on-screen messages.

If you can get the monitor to stay on, try turning down the brightness to see if the backlights will stay on longer.

[miroja]

Re: HP ZR2740w almost dead

Thanks for answer. I found similar circuit diagram with MTV416GMV IC also, (service manual from other brand of monitor), but as you wrote also, there are ports used to others functions.

When I switch-on mains without connection to NB, I have no info on screen (NO SIGNAL or NO CABLE CONNECTED or similar message on screen). Display is completely dark, without backlight also. After a few seconds blue status LED is changed to amber..that is all. According to my experiences, there should be any message on screen about missing signal on screen.
I tried to connect monitor to NB via Display port and amber LED status has been changed to blue.. and in next 1-2 seconds I had picture :-) .
But… after next 30-35 sec (I checked it more times), goes LED status blue to OFF ??? monitor was is still running. Strange is also, that I have no ON-SCREEN info on panel. When I press “+” or “–“ button, brightness is changing, but I have no info about it (brightness string bar is missing on panel). Also button “source” is probably changing the source of the signal. I have picture/no picture on screen – when I am pressing this button twice.
Yesterday was monitor running about 30 min, after that - again black screen. I tried to measure capacitors in feeding level +5V, +3,3V and 1,2V today and all seems to be ok (capacity and ESR also).
Today is running about 60 min (PCB are “fixed” only temporary and isolated by thick paper).
ON SCREEN is not so important, but why is status led switched off after 30 sec. when monitor is running. I think that there is still something wrong (missing communication between ICS responsible for identification of signal and steering processor??? ) and I expect next problems with this HP monitor.
Do you have any hint what can I check, measure ?
Thanks in advance.

[fzabkar]

Re: HP ZR2740w almost dead

When i switch on mains, status LED goes to blue, after a few seconds to amber. It seems all OK, because i have no connection to PC. But i have no background light.

Should your monitor briefly display "no signal", and are you saying that this message is not being displayed? Otherwise the behaviour seems normal to me.

[fzabkar]

Re: HP ZR2740w almost dead

This thread has some relatively clear photos of the PS PCB:

http://forum.iwenzo.de/hp-zr-2740w-s...e--t59434.html
http://forum.iwenzo.de/attachment_pr...d_file&id=9299
http://forum.iwenzo.de/attachment_pr...d_file&id=9301

The label says ...

TATUNG
Model: TPC-11536
Type: PWB-1421
Input: 100 - 240Vac
Output: +5V/4A
+12V/1.5A
-35.5V/2A

Attached is a section of a circuit diagram for a different monitor. It shows the pinout of the MTV416GMV microcontroller, albeit with different functions for each of the ports.