HP ZR2740W troubleshooting

[Stifle9]

First time poster here, hoping to get some insight into what is going wrong with this monitor.

Monitor History - HP ZR2740W, given to me because it was faulting, I accepted it because of the retail value and possibility of resurrecting. I was told that it had been used for the past year and that the person I got it from was told that it was probably a back-light issue.

The issue - The monitor has a repeatable fault where if the power supply (separate switch near power cord) is turned on and the monitor is being fed a display signal (through DVI, checked with another monitor, and it then powered on with the power button on the front... the LED indicator will light up blue for the power-on cycle time of about 2 seconds with no display showing, and will then flash on then immediately off without any display showing. The blue LED light will remain constant the entire time this is going on but will turn itself off after ~30 seconds.

I have pulled out the power board and have inspected the board carefully (admittedly I am only capable of looking for obvious goo, bloating, etc.) and I see no sign of any bad capacitors, anything blown or soldered improperly. The only thing that I noticed was that there was some residue the seemed to be a spill of some kind of orangey/brown colored liquid that extended across the length of the board - I cleaned off with alcohol and have put the board back in and there was no change to the fault.

I count 20 capacitors (lelon) on the board and can only note that some of the tops of the caps seem to be more deeply imprinted with the cross-hatch than others and have slightly more curvature within each segment than others do, IE: some look more flat than others, but none are obviously bulging.

I am new to the whole scene and have not been able to find any threads of people repairing this particular model before, on this site or googling for other threads for a few hours

I have attached images of the front and back of the board.

Ideas?

[Stifle9]

Re: HP ZR2740W troubleshooting

Does anyone have any experience with this monitor or problems similar to what I have described above?
Could I give any further description that would help out?

[budm]

Re: HP ZR2740W troubleshooting

It has LEDs backlights, 6 strings total (6 filter caps on the left side of the board) from what I can see on the connector P804 (VO1 ~6).
So if one of the LED sting has open circuit due to bad LED, the LED driver circuits will shut down, or if one of the wires is shorted to the metal chassis, it will also go into shutdown.
So check and see if you have any DC voltages on those VO1~6, you may have to cycle the monitor on and off to look at each pin.

[Stifle9]

Re: HP ZR2740W troubleshooting

I have the monitor torn apart on my desk in my classroom at school so I will get back to it and start testing that on Monday budm, thanks for the suggestion. So I will connect everything together but keep the power board open to test with my MM for voltage

[Stifle9]

Re: HP ZR2740W troubleshooting

Ok so here goes the testing results from budm's suggestion to test the DC voltages out from block P804 (pics of setup attached).

Every cable for normal operation of the monitor is attached sans the USB hub from the controller board. The power is switched on and the monitor is powered on via the power button for each test. The monitor is being fed a live signal through the DVI port before the monitor is powered on.

COM lead is stuck to 1.GRD for each test and live test lead is moved through the even numbered pins to check voltage output on each.

I both leads before I power on the monitor and the results are the same for pin 2, 4, 6, 8, 10: voltage reading is falling during the power-on sequence, but once the monitor flashes on them immediately off (see original post) the voltage on 2,4,6,8,10 jumps to 30V then drops off quickly at first then slower over time (y=1/x).
Pin 12 is the same situation only it jumps to 60V before dropping off.

Hope this helps, what does this mean?

[Stifle9]

Re: HP ZR2740W troubleshooting

Shameless bump - really interested in getting this problem resolved

Would the slow leaking of voltage from the P804 block after the flash mean that the capacitors on the power supply board were bad?

I have recorded the list of capacitors though I have no idea where I could acquire a set of replacements, I could use some help with that if it would be a good idea given the data so far. I dont even know where to start or what style of caps to order.

All caps are Lelon brand:

2x 250V 220μF A114(M)
6x 50V 220μF A101(M)
3x 50V 100μF A040(M)
1x 25V 470μF A110(M)
6x 16V 1000μF A114(M)
2x 25V 680μF A114(M)

[Stifle9]

Re: HP ZR2740W troubleshooting

Looking for some more insight on this issue if anyone can help. Sorry to be a pain and bog up the board

[Davi.p]

Re: HP ZR2740W troubleshooting

Hi, from your first post i don't have really understood the led sequence, maybe i am so bad in english, but this i think is not so important.. i've never seen a power board like this, is it a 27 or 40 inch? In your school are all so big? ...
Watching P804, VO1 is connected to Anode of D814 that is the negative output of a bridge rectifier and the + output of it seems connected to heart ground trough a low value resistor R861 (maybe less than 1ohm, i cannot understand the color code) so VO1 must be negative? Someone tell me if i'm wrong; and VO2 to which point is connected?
Anyway 8 ics for a powersupply is too much for me

[Stifle9]

Re: HP ZR2740W troubleshooting

The monitor is a 27in yes and not many in the school are this large but as it represents a significant investment initially, I thought that I could give it a try.

I assumed in my testing of P804 that all of the ground wires were essentially common so in testing I placed the common/anode on the Multimeter on pin 1 and left it there while moving the cathode/live from pin 2, 4, 6, 8, 10, 12... I think that I may have made a mistake here in testing P804...

How should I test P804 for output voltage if not the way I did it the first time? Could it be as simple as testing pin 2.(V01) with pin 1, then pin 4.(V02) with pin 3?

[Davi.p]

Re: HP ZR2740W troubleshooting

You have tested properly, i espected negative outputs but i dont understand well this circuit, there are many points unclear.. if there was a schematic maybe is better.. but i can't find it.

[momaka]

Re: HP ZR2740W troubleshooting

Hard to say if the issue is in the LED inverters or the LED backlights themselves.

It would be best if it was possible to test the LED strips one by one. But I don't see any "clean" ways of doing that. By not "clean", I mean that you will probably either have to pull a bunch of components off the board (notably, the rectifier diodes), or cut wires (or traces on the board) to all of the LED lights so that we can enable only 1 LED strip to be on at a time. But I rather do that as a last resort (that is, unless someone has a better idea of how to go about this or you don't mind trying a more "unorthodox" testing procedures.)

So to keep it "clean", let's start with the LED light rectifier diodes. That would be diodes D814, D815, D817, D819, D821, D823, and etc. all the way up to D832. Measure the resistance across each and report the results here. We are looking for potentially shorted rectifiers showing less than 100 Ohms of resistance.

Another thing worth checking before getting deeper into the monitor would be the voltage on Pins 1 and 11 on the connector P803. With older CCFL-lit monitors, most would display an image on the screen regardless of whether there was backlight or not (you just wouldn't see anything if there wasn't any backlight). However, I wonder Pin 1 or Pin 11 (5v-sense) have anything to do with detecting whether the backlight is working or not (and thus possibly telling the main board to shut off the monitor if it isn't).

Aside from that, the last "clean" thing to try would be to replace the 6 electrolytic caps for the LED backlight. I'm guessing that is either the 6x 50V 220μF or 6x 16V 1000μF (probably the 50V ones though). If there is no specific series written on them (usually a 2 or 3-letter code), the I would suggest you just get something like Panasonic FC, FR, or FM (or similar equivalents such as Rubycon ZL and Chemicon KY and KZE) and changing them out. But if you decide to change those caps, you might as well recap the whole monitor. That way, we will know for sure it is not a capacitor issue.

[stj]

Re: HP ZR2740W troubleshooting

led strips cant fail.
they consist of a number of groups that are strobed in sequence very fast to keep the power level low.
if an led fails you will only lose around 7 leds from the strip.

[Davi.p]

Re: HP ZR2740W troubleshooting

stj is there any feedbck circuit that shuts off all the line or leds stripe continue to work without those 7?

[stj]

Re: HP ZR2740W troubleshooting

led backlights use a controller chip,
the chip is a combination of a current-regulator and a sequencer.
i dont know if it has overcurrent protection - i think it wouldnt need it if the current was regulated.

id the led driver chip & get a datasheet.
also, look real close at the top of the chip.
i'v seen a couple with a tiny hole burned through them were one of the internal fets died.

[Stifle9]

Re: HP ZR2740W troubleshooting

I imagine the backlight controller chip is not on the power board that I have attached pictures for. I can visually inspect the chip to see if anything looks amiss if you give me an idea of what it looks like and where it might be. There are several other boards that I can see attached to the video board.

ill run those tests that momaka has outlined and report back

[Stifle9]

Re: HP ZR2740W troubleshooting

ok the results are as follows from testing what Davi.p suggested:

Testing Rectifier Diodes on back of power board.
Tested the 12 sequentially numbered in order from D814 to D830 and they all tested between 5.12k ohms and 5.34k ohms.

Testing P803, pins 1 and 11 with adjacent ground pins. Test conducted in the same manner (everything hooked up with life video feed coming to monitor, power switched on then button powered on, monitor flashes on/off about 2 seconds afterwards then screen remains dark)
Pin 1 showed 2.19V after switching on but the voltage drops to 1.42V after the power button is pressed and just before the flash occurs, this voltage remains steady afterwards for several seconds until i quit testing.
Pin 11 showed a steady 5.17V after the power switch is thrown, voltage remains constant through power button and flash on/off sequence.

Regarding the series codes for ordering more caps, where would one search for those on the body of the caps?

[momaka]

Re: HP ZR2740W troubleshooting

led strips cant fail.

I'm not sure about that.
I think I do remember reading in one of the TV or monitor threads that either budm, tom66, or someone else reported an LED strip going bad (don't remember if it went open circuit or short circuit).
I imagine the backlight controller chip is not on the power board that I have attached pictures for. [/quote]
It should be. Probably one or two of the SMD ICs on the bottom of the board (I810 and I815?) could be responsible for driving and monitoring the LED backlights. It has to be that way,
[quote=Stifle9]because all of the LED driver transformers' primaries are wired in series (the two wires sticking out of each LED transformer). That means that all of the LED strips are driven either together or possibly in 2 groups. Either way, if one LED strip is either open or shorted, it will cause the voltage for its driver transformer to go up or down (depending on failure condition). The jumpers next to the caps in the LED inverter section are there to relay a voltage level from each LED transformer to tell the controller(s) whether each LED strip is behaving properly. If there is a fault, the entire LED driver circuit will shut down. That's why we need to test each LED strip separately with each LED driver transformer. This would make it possible to narrow down the problem and tell if the fault really is with an LED strip or the controller itself. (...Or possibly something else. Though it should be noted here that LED transformers have much lower voltage output than CCFL inverter transformers, so failure is unlikely.)

Tested the 12 sequentially numbered in order from D814 to D830 and they all tested between 5.12k ohms and 5.34k ohms.

They are likely fine then.

Regarding the series codes for ordering more caps, where would one search for those on the body of the caps?

It's different for every cap manufacturer, but usually you'll see it somewhere printed on the sleeve just like the capacitance and voltage. Look on all sides of the caps and see. In rare cases, some cheap caps don't have a series. But I don't think that would be the case with Lelon here. They usually do have the series printed on them. May be something like RXA or other 2 or 3 letter code.

[stj]

Re: HP ZR2740W troubleshooting

the 3rd party led kits use 2 wire led drive,

but all the factory original ones i'v seen use 10pin flex cables.
using 3 common and 7 seperate drive signals.

follow the flex cable from the panel to find the driver - the chip is usually very close to the connector.
all the ones i'v seen sofar btw have been square surfacemount packages with pinless connections on all 4 sides and a center heat-plane under them ffor cooling like soic fets use.

[budm]

Re: HP ZR2740W troubleshooting

You can put DC amp meter in series with each strip of the LED string to see which one is not drawing the current before it goes into shutdown mode. The circuit will shutdown if it detects short or open circuit in any one of the string. Most common failure in LED backlights is due to open LED.

[stj]

Re: HP ZR2740W troubleshooting

good luck with that theory,
i'll post some foto's of a strip, and driver board soon.