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

Quote:
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, 04:08 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, 04:13 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, 06:27 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, 07:08 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, 03:28 AM   #86
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Default Re: HP ZR2740w almost dead

Quote:
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, 03:52 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, 04:31 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, 07:21 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, 02:07 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, 11:58 AM   #91
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Default Re: HP ZR2740w almost dead

Quote:
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, 02:05 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, 02:44 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, 04:01 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 07-20-2017, 09:23 AM   #95
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Default Re: HP ZR2740w almost dead

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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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Old 11-11-2017, 05:58 PM   #96
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Default Re: HP ZR2740w almost dead

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Originally Posted by budm View Post
The PFC Voltage booster should boost the Voltage from around 325V (230 ac line x 1.414 = 325V) to >360VDC which is required by LED driver circuit to function.
Helo,
My case stops here.
Everything is disassembled on my desk.

When I turn on main switch S801 LED are On with hight backlight (bright), after few seconds thay dimm to 50% (let's name it like that, but it's not mesured 50%), and after another few seconds thay dimm even more - again let's say 25% of light.
After that, they stay lighten up all the time but very dimmed.
No input signal is given form PC, but there are pull-up resistors to force 3.PS-ON and 2.On/Off - so, turn on power supply and force LEDs to light up.

Force switching power supply and backlight LEDs
3. PS-ON pulled up to 5V (I've mesured 4.7V)
2. On/Off pulled up to 5V (I've mesured 4.7V)
1.V.adj pulled up to 5V (I've mesured 4.7V)

This gives exactly what I wrote at the begining.


Other tests
- fuse F801 has 0.4Ohm resistance
- before turning F801 on I get 5.2V on 5V rail on P803
- before turning F801 on I get 0.1-0.3V on 12V rail on P803
- before turning F801 on I get 1.9V on 3.PS-ON on P803
- before turning F801 on I get 1.9V on 2.On-Off on P803
- before turning F801 on I get 1.9V on 1.V.adj on P803
- after turning F801 on, I get 11.4V on 6 and 7 pins on P803
- testing voltage on P804 (switch on and off every time) gives ~30V on every pair - every time and it stays 30V even after voltage drops from 400 to 300V on big caps (C807 and C802)
- Mesuring 5V and 12V on P803 I have notice huge ripples - see attachement
This ripple is higher when I read 400V between caps and drops a little after voltage drop to 300V (on caps)

When I switch main power-switch S801 on, I get 400V between C807(-) and C802(+) for about 3.5s and after that it drops to ~300V (see attachement).

Reading other posts about this monitor model I think there's problem with PFC Voltage Booster, but I have no idea how to test it?
How to check if it's I801 or sth arround?
- diode D802 gives 0.48 forward Voltage and OL backwards in diode test mode - so it's fine
- transistor Q801 - soldered out gives:
- S > D 0.53V (red to S to black to D) in diode test mode,
- D > S OL (red to D to black to S) in diode test mode - correct
- diode D803 - forward voltage 0.58 (opposit way OL) - correct

Second issue are ripples on 5V and 12V rail on P803.
While I pulled up 3.PS-ON an 2.On/Off I can see huge ripples during 400V PFC booster work and little bit smaller ripples during 300V PFC Booster work. Should't the ripples be much smaller?
Can you look into attachment and compare it with your knowledge and experience?

What else can I test to find this broken piece of board?

There's one more thing I have noticed looking to other people photos.
Someone have replaced 7 capacitors (LED power): C864, C862, C854, C852, C848, C847 and extra C883 - which is much smaller on other photos.
Capacitors I have now are all 50V 220uF - so question is what values should be there, because I cant find angled photo ;-) and from the top they look like C835 for example?
Attached Images
File Type: png 5V and 12V during 300V between caps C807&C802.png (81.3 KB, 4 views)
File Type: png 5V and 12V during 400V between caps C807&C802.png (112.9 KB, 2 views)
File Type: jpg PWB-1421 top.jpg (615.3 KB, 4 views)
File Type: jpg PWB-1421 bottom.jpg (727.4 KB, 5 views)
File Type: png 400V-300V with description.png (29.0 KB, 5 views)
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Old 11-12-2017, 12:11 AM   #97
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Default Re: HP ZR2740w almost dead

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Originally Posted by Snout View Post
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.
I can add, as an aside, that if you have a _lot_ of old junk lying around.. in my case a later-than-2010 27-inch iMac (with dead graphics card), that the display in it was exactly the same! Except, of course, that the connectors were in the wrong places so it wouldn't fit in the HP's original case. But hooking up the HP's control circuits to the Mac's screen also produced a working monitor. Of course with the HP's limitations of no OSD or menus etc. ... Strange how things work out sometimes. (It just occurred to me to post this here, now that I got notified of a post in this thread.)
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Old 12-05-2017, 11:08 AM   #98
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Default Re: HP ZR2740w almost dead

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Originally Posted by mikolajj View Post
Helo,
My case stops here.
Hello,
finally I had enough time to investigate everything again.

The problem was broken LED stripe connector, when it was pressed everything was fine. After a moment everything went wrong. That's why I get 30V per LED power line every time.

I have soldered new connector and everything is fine now. Everything works like a harm.

Good thing is that during replacement of caps I have wrote down their values. I this is what I have found:

Code:
 Motherboard
C66	100uF	16V		⌀ 8mm	h 8mm
C67	100uF	16V		⌀ 8mm	h 8mm
C42	100uF	16V		⌀ 8mm	h 8mm
C48	470uF	16V		⌀ 8mm	h 9mm
C45	220uF	25V		⌀ 10mm	h 13mm
C50	220uF	16V		⌀ 8mm	h 8mm
C15	4.7uF	50V		⌀ 5mm	h 12mm
C51	100uF	16V		⌀ 8mm	h 8mm
C52	100uF	16V		⌀ 8mm	h 8mm
C55	100uF	16V		⌀ 8mm	h 8mm
C57	100uF	16V		⌀ 8mm	h 8mm
C60	100uF	16V		⌀ 8mm	h 8mm
C59	100uF	16V		⌀ 8mm	h 8mm
C70	100uF	16V		⌀ 8mm	h 8mm
C71	100uF	16V		⌀ 8mm	h 8mm
C521 	100uF	16V		⌀ 8mm	h 8mm
C529 	220uF	25V		⌀ 8mm	h 8mm
C515 	10uF 	16V		⌀ 4mm	h 8mm
C514 	4.7uF	50V		⌀ 5mm	h 12mm
C530 	220uF	16V		⌀ 8mm	h 8mm
C528 	220uF	16V		⌀ 8mm	h 8mm
C527 	220uF	16V		⌀ 8mm	h 8mm

Power supply board
C840	100uF	100V		⌀ 10mm	h 17mm
C823	100uF	50V		⌀ 8mm	h 12mm
C826	680uF	25V		⌀ 10mm	h 17mm
C831	1000uF	16V		⌀ 13mm	h 17mm
C825	680uF	25V		⌀ 10mm	h 17mm
C832	1000uF	16V		⌀ 13mm	h 17mm
C833	1000uF	16V		⌀ 13mm	h 17mm
C835	1000uF	16V		⌀ 13mm	h 17mm
C834	1000uF	16V		⌀ 13mm	h 17mm
C836	1000uF	16V		⌀ 13mm	h 17mm
C828	400uF	25V		⌀ 10mm	h 17mm
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