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...
cmg
Member
Last Activity: 03-24-2019, 04:03 PM
Joined: 12-07-2016
Location: London
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Re: HP ZR2740w almost dead
This was a while ago.. I just remembered I put more info on the repair here:
[url]https://www.badcaps.net/forum/showthread.php?p=758118#post758118[/url]
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.Re: HP ZR2740w almost dead<br /> <b...one has one ofLeave a comment:
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Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)
Updating this due to comments on the other thread.
Pic shows the strip fixed, then tested using a little constant current source PCB (showing 33V). Finally i tested it in situ. This WAS necessary because the connector is very dodgy and once I didn't solder it very well, finding it failed again when I had reassembled the panel....Leave a comment:
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Re: HP ZR2740w almost dead
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 "[I]- push forward a couple of the white plastic clips found underneath this. Every one i did broke off...[/I]" 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-...Leave a comment:
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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 [U]very[/U] tough...Leave a comment:
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Re: LED blacklight flickers at low brightness, PFC output voltage unstable. Help!
Finally! Got it
It was the PFC controller IC. Will post some details later.Leave a comment:
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Re: LM270WQ1 SD F1 - iMac 27in A1419 LCD
Its almost the same panel as in the HP ZR2740W monitors i have. Mine is LM270WQ1-SDDA. *Perhaps* some chance you could swap the TCON from one of these if you find a broken one on eBay. They are pretty poorly made (not what i was expecting from HP) so you may well see one.
I needed to get spare backlight LEDs and had a real job trying to do so. I dont think you'll be able to buy the TCON unless someone has one from a broken LCD on eBay.
Just because the pic is fine on the external monitor doesnt mean the problem is...Last edited by cmg; 04-29-2017, 05:31 PM.Leave a comment:
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Re: Transformer for HP zr24w
No, that is normal; put it back!
The resistance (i.e. impedance @ 0Hz) is expected to be low but the impedance at its operating frequency (many kHz) will be fine. If the transformer were open circuit you would diagnose that with a multimeter. If it had a short, then as Bud said, it would be visibly toasted and blown loads of other stuff including the fuse.
I suggest it is either:
- the PSU has been signaled to turn off by the control circuits as Bud suggested (check "ON/OFF")
- a problem...Leave a comment:
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Re: HP ZR2440w backlight cutting out
Ginko - you have a very similar problem and circuit [URL="https://www.badcaps.net/forum/showthread.php?t=61635"]to the one i am trying to diagnose[/URL]. From your pics I can see the ZR2440W is like a cutdown version of the 2740 that I have. Probably they've used the same controller ICs.
Please try altering the brightness on the front panel control and see if it becomes stable at high brightness. I wasn't clear from the above if you tried swapping the LCD panel (i.e. including the backlights) from one of your good monitors...Leave a comment:
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Re: LED blacklight flickers at low brightness, PFC output voltage unstable. Help!
.. bit more progress.
Firstly i looked at the AC output of the transformers which are driven by the DC-DC converter. When the monitor becomes unstable, the frequency is modulated and ultimately drops out. It starts off at about 150kHz. Because the frequency is unstable my view is that the problem is in the DC-DC converter or its control.
I traced the control through the Opto-Isolator I812. This in turn is controlled by another TI chip - I810, a [URL="http://www.ti.com/lit/ds/symlink/tl103wa.pdf"]Z103WA[/URL]....Leave a comment:
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Re: LED blacklight flickers at low brightness, PFC output voltage unstable. Help!
Ah.. made some progress. The controller IC I811 is [URL="http://www.ti.com/lit/ds/symlink/ucc25600.pdf"]a TI 25600 type[/URL], so now i can see that this is where the brightness control is implemented.
However, the whole circuit (PFC plus this DC-DC converter) will all be pulsing so I'm not sure how best to work out where the cause is.
Thanks!Re: LED blacklight flickers at low brightness, PFC output voltage unstable. Help!
Ah.. made some progress.Leave a comment:
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Re: LED blacklight flickers at low brightness, PFC output voltage unstable. Help!
Thanks for the fast response Bud. The boards are the same as in
[URL="https://www.badcaps.net/forum/showthread.php?t=42720"]this[/URL] thread and [URL="https://www.badcaps.net/forum/showthread.php?t=42498"]this [/URL] one. In fact i see you drew a helpful diagram of the LED driver a while ago.
I've attached a couple of pics of my PSU board. (note:
- wires soldered over C807 was to measure voltage on meter without holding it.
- Cap over D803...Leave a comment:
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LED blacklight flickers at low brightness, PFC output voltage unstable. Help!
Hi All.
I have a problem which is hopefully relevant for other readers of the forum and other monitors as it is concerning the PSU and LED backlight driver. The symptoms are that as the brightness is reduced using the front panel controls, the screen starts to flicker quite annoyingly. I believe this is a fault in the PFC circuit. The output voltage from the PFC circuit pulses in correlation with the flickering. This is on an HP ZR2740W 27" monitor.
The PFC controller is a 28051 (see [url]https://cdn.badcaps-static.com/pdfs/26e77e0c77a55d42544fbd898502619c.pdf[/url]),...Last edited by cmg; 04-13-2017, 04:25 PM. -
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...Last edited by cmg; 02-15-2017, 06:11 PM.Leave a comment:
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Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)
OK.. I fixed it now! This was thanks to the seller mentioned above finding the right LEDs.
Soldering the new ones on was very tricky indeed. The first few i did look pretty awful and eventually the don't look too far off the original ones.
The LEDs were closely spaced so heating the whole strip seemed like a bad idea. The most successful method i had was to tin the pads and the underside of the LED with an iron, then melt the solder on the pads with the hot air set at 315C. Then i'd slowly lower...Leave a comment:
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Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)
Thanks for the advice. I'll give it a try on some scrap PCBs while waiting for the new LEDs.Leave a comment:
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Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)
No. I've got flux and lead free solder paste in the mail. Actually I didn't realize flux will help with desoldering. I'm new to hot air soldering. I'm planning to solder the new LEDs on with solder paste and hot air. It is not possible to solder these with an iron as the pad is right underneath. When i get the paste and flux i'll practice with some scrap PCBs. Hopefully small SMD power transistors / voltage regs will seem similar to solder....Leave a comment:
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Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)
Hi. The seller's page is here: [url]http://www.ebay.co.uk/usr/lelos2[/url]
He's very helpful and he has lots of LEDs listed. I haven't yet got the LEDs so I can't say if they are definitely right.
Thanks for the videos - that was interesting. The strip i have is small and narrow (see pics). I think I'll continue to try heating from above with the rework gun. I was using the narrowest nozzle (<2mm dia); perhaps I should use a larger one and turn up the flow and/or temp. The specs for...Leave a comment:
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Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)
Thanks Pete.
Well, Google hasn't shown me any hits at all that point to being able to find a replacement strip so that is not an option anyway. It is definitely special for this panel as the PCB has the panel model # on it.
When i was trying to remove it i was focusing on the side with the A, K pins and didn't think of the huge heat pad underneath the other side. Maybe better next time as there are a handful i need to replace. I cracked the lenses off when removing the strip....Leave a comment:
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Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)
Hi. Thanks for the help. I think i've got the right parts on order now thanks to Mr 'lelos2' on eBay.
I had seen the Osram ones looked similar but they were not the same. The parts he found were Lumileds LXML-PWD9N, 3W 3V 3030. They certainly are the same voltage, have the same type of lens and have the same solder pad pattern. I'm awaiting the order, so will be able to try in a couple of weeks.
My advice is that it is really hard to find the exact correct LED, and that I found someone...Last edited by cmg; 01-14-2017, 05:27 PM.Leave a comment:
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