Re: HP ZR2440w backlight cutting out
I was able to overcome the thermal mass problem by turning up the temperature on the soldering iron, I was reluctant to do this for fear of damaging adjacent components, but gave it a try anyway. It was still a very long and tedious process desoldering all 25 capacitors from that board. Of course, replacing those capacitors didn't fix the problem either as my luck has it. I really thought it would since the strong temperature correlation points to a capacitor problem.
I was able to solder in a test wire to the output voltage for...
Ginko
Member
Last Activity: 05-26-2015, 01:22 AM
Joined: 05-02-2015
Location: NH
-
Re: HP ZR2440w backlight cutting out
I'd been thinking more about this issue, and came back to the temperature correlation. That really seems to point to a capacitor problem. There is one suspect capacitor on the data board, a 10uF 50V one. This one is not in parallel with other capacitors. It measures within spec at 1khz, but when I drop the frequency down to 100hz, its capacitance jumps up to 12.35uF. That's outside the +/- 20% tolerance. In addition, the Rs measures 45ohms at 100hz. There is another identical 10uF 50V cap on the board that also isn't in parallel, and this one...Leave a comment:
-
Re: HP ZR2440w backlight cutting out
Unfortunately I had absolutely zero luck getting the datasheet for the IC. The writing on the chip is horribly worn down and I wasn't able to pull anything up at all despite trying several combinations of possibilities. I thought maybe I could find what the IC was if I could get the datasheet on the power board itself, Tatung TPC 06034 PWB 1429. Zero luck there too.
If I had a scope I could at least determine if the problem is happening due to LED power or the data board, but I don't.Leave a comment:
-
Re: HP ZR2440w backlight cutting out
Is it possible it might be the input filter cap I wasn't able to replace on the SMPS? I'm guessing probably not, but I'll check its esr later. If it's the dimming control signal, maybe that suspect capacitor on the data board is to blame. It would be nice if I could swap the data boards but they aren't pin compatible. I'll see if I can get the number off the LED driver IC and look up the data sheet.Leave a comment:
-
Re: HP ZR2440w backlight cutting out
Ok. I disassembled the other zr2440w and compared the panels. The older one is LG LM240WU8 SLA1, and the newer is LM240WU8 SLA3. Even though both cables were pin compatible, I was paranoid about frying things and wanted to check the voltages. Unfortunately it doesn't look possible to get at the SMPS PCB with probes when the backlight cable is connected to the panel because the cable is too short and the shield has to basically be on the panel like it is normally.
I looked up the datasheets on both and confirmed they are in fact pin...Leave a comment:
-
Re: HP ZR2440w backlight cutting out
I will see if it is possible to swap panels to pinpoint the issue. If it's not the panel, the only other thing I can think of is checking the output voltage of said boost converter. I don't have a scope so I can't look at the waveform. If it does end up being the LEDs themselves, I presume that isn't fixable given it is inside the panel.Leave a comment:
-
Re: HP ZR2440w backlight cutting out
Ok, I laid the two boards on top of the shield and lined up the cables to show what goes where. The cable that goes nowhere is the data cable for the panel. The top left cable in picture 1 goes to the USB ports. The bottom left cable goes to the buttons on the front of the monitor. The one on the right as can be seen goes to the SMPS, and the bottom cable is the data cable to the panel.
I see some inductors and diodes right before the output to the flat flex. I did not measure voltage here with my multimeter before, so I will see...Leave a comment:
-
Re: HP ZR2440w backlight cutting out
Sorry, I was in a bit of a hurry when I took the pictures. I will get some additional ones that make things clearer. The flat flex connects to the back of the SMPS in the bottom right of picture 2 right above the cutout where the flash spot is. It is labelled P851.Leave a comment:
-
Re: HP ZR2440w backlight cutting out
Some progress and pictures. I disassembled the monitor again and have started testing the capacitors on the data board. C193 and C192 had a negative residual voltage of around 1.9v. These two are in parallel and are rated 470uF 16V and 100uF 16V. One is a capxon and the other a lelon. In circuit capacitance test yields 534uF. ESR/Rs tests show 130mOhm @ 100hz, 120mOhm @ 120hz, 44mOhm @ 1khz, 50mOhm @ 10khz, 63mOhm @ 100khz.
There are 25 capacitors on this board. I have to determine if each is in parallel with others first then...Leave a comment:
-
Re: HP ZR2440w backlight cutting out
Ok, finally was able to observe the LED when the backlight dropped out. It was difficult because it happens so fast that by the time i look at the LED the backlight was back on again. The LED does stay lit during the times when it cuts out.
The ESR meter arrived yesterday and if I have time today I'll attempt to get some pictures. I did test the old lelon caps from the SMPS and the worst ESR I got was from the 10uf 50v capacitor which measured 1.78 ohms or so, but for low value capacitors I believe that's within spec.Leave a comment:
-
Re: HP ZR2440w backlight cutting out
I will try to take note what the power indicator led is doing next time the backlight cuts out. None of the fittings are pin compatible except the LCD panel itself (which is LG). I am not sure if the backlight is built into the panel and therefore shares its data cable or if it is separate. When the ESR meter arrives in a couple of days, I'll disassemble the monitor again to test the capacitors, and take pictures of everything....Leave a comment:
-
HP ZR2440w backlight cutting out
I have a set of HP ZR2440w LED backlight monitors. One of them is having issues with the backlight. On certain backgrounds (like the one at php.net) I notice it flickering. The other zr2440w has no such flicker problem. The major issue with it is that the backlight cuts out for a fraction of a second intermittently. This happens a lot more frequently when it's first turned on after it has been off and cold overnight, so it seems to be temperature related. I suspected the capacitors in the power supply might be bad, so I opened up the monitor to have a look.
They all looked fine... -
Re: New Members - please post your introductions here
Hello, I've been getting into electronics the last couple of years and am currently attempting to repair a HP zr2440w monitor that's having LED backlight issues. I recapped the SMPS board in it and that didn't resolve the issue, so I'm hoping to get more ideas of where to proceed on here.Leave a comment:
No activity results to display
Leave a comment: