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Forum: Troubleshooting Computer Displays 07-18-2017, 01:07 AM
Replies: 108
Views: 27,267
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 07-17-2017, 03:31 PM
Replies: 108
Views: 27,267
Posted By cmg
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/showthread.php?p=758118#post758118

Btw, if anyone has one of these for parts, I'd like...
Forum: Troubleshooting Computer Displays 07-17-2017, 03:26 PM
Replies: 22
Views: 5,676
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 07-17-2017, 02:52 PM
Replies: 108
Views: 27,267
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 07-16-2017, 05:27 PM
Replies: 108
Views: 27,267
Posted By 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...
Forum: Troubleshooting Computer Displays 04-30-2017, 05:53 PM
Replies: 5
Views: 1,680
Posted By cmg
Re: LED blacklight flickers at low brightness, PFC output voltage unstable. Help!

Finally! Got it :cool:

It was the PFC controller IC. Will post some details later.
Forum: Troubleshooting Computer Displays 04-29-2017, 05:29 PM
Replies: 3
Views: 3,152
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 04-29-2017, 05:11 PM
Replies: 25
Views: 6,848
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 04-29-2017, 04:58 PM
Replies: 24
Views: 8,565
Posted By cmg
Re: HP ZR2440w backlight cutting out

Ginko - you have a very similar problem and circuit to the one i am trying to diagnose (http://www.badcaps.net/forum/showthread.php?t=61635). From your pics I can see the ZR2440W is like a cutdown...
Forum: Troubleshooting Computer Displays 04-14-2017, 06:05 PM
Replies: 5
Views: 1,680
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 04-14-2017, 03:08 AM
Replies: 5
Views: 1,680
Posted By cmg
Re: LED blacklight flickers at low brightness, PFC output voltage unstable. Help!

Ah.. made some progress. The controller IC I811 is a TI 25600 type (http://www.ti.com/lit/ds/symlink/ucc25600.pdf), so now i can see that this is where the brightness control is implemented.
...
Forum: Troubleshooting Computer Displays 04-13-2017, 06:07 PM
Replies: 5
Views: 1,680
Posted By cmg
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
this (http://www.badcaps.net/forum/showthread.php?t=42720) thread and this (http://www.badcaps.net/forum/showthread.php?t=42498)...
Forum: Troubleshooting Computer Displays 04-13-2017, 04:22 PM
Replies: 5
Views: 1,680
Posted By cmg
Question 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...
Forum: Troubleshooting Computer Displays 02-15-2017, 06:09 PM
Replies: 108
Views: 27,267
Posted By 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...
Forum: Troubleshooting Computer Displays 02-15-2017, 05:41 PM
Replies: 22
Views: 5,676
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 01-24-2017, 05:26 PM
Replies: 22
Views: 5,676
Posted By cmg
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.
Forum: Troubleshooting Computer Displays 01-18-2017, 03:56 PM
Replies: 22
Views: 5,676
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 01-17-2017, 06:04 PM
Replies: 22
Views: 5,676
Posted By cmg
Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)

Hi. The seller's page is here: http://www.ebay.co.uk/usr/lelos2

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...
Forum: Troubleshooting Computer Displays 01-15-2017, 09:58 AM
Replies: 22
Views: 5,676
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 01-14-2017, 05:20 PM
Replies: 22
Views: 5,676
Posted By cmg
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...
Forum: Troubleshooting Computer Displays 01-14-2017, 12:30 PM
Replies: 22
Views: 5,676
Posted By cmg
Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)

I had naively thought that the LEDs might be generic or easy to find. This is definitely not the case. My advice for anyone else looking for backlight LEDs chips is to contact 'lelos2' on the most...
Forum: Troubleshooting Computer Displays 01-14-2017, 12:26 PM
Replies: 108
Views: 27,267
Posted By 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....
Forum: Troubleshooting Computer Displays 12-29-2016, 04:22 PM
Replies: 22
Views: 5,676
Posted By cmg
Re: Sourcing replacement backlight SMD LEDs or Strips (LG panel)

So I found the LEDs are coded with a 4 digit number which represents the x,y dimensions in tenths of mm. For instance there is 3528 which is 3.5mm x 2.8mm.

Mine are 3.0mm square so I'm looking for...
Forum: Troubleshooting Computer Displays 12-29-2016, 04:11 PM
Replies: 108
Views: 27,267
Posted By 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...
Forum: Troubleshooting Computer Displays 12-28-2016, 05:15 PM
Replies: 22
Views: 5,676
Posted By cmg
Sourcing replacement backlight SMD LEDs or Strips (LG panel)

Hi. I would like to gather advice about sourcing replacement SMD LEDs and/or LED backlight strip PCBs. As this is a general issue I thought we can have have a new thread.

As you will see here...
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