Benq v2210 Eco - one backlight strip not working

[martinlink]

Hey guys and gals,

my lovely LED monitor decided to discontinue its (until now) perfect service. Only the top half is brightly illuminated, while the bottom is about 50% dimmer, though still legible.

I dismantled the monitor and tested the 2 LED backlight strips by connecting them to the 2 different sockets on the controller module (dunno how you call it).

I found that both the strips work when plugged into the top socket, and neither work when plugged into the bottom socket. So it seems that the problem lies somewhere in the LED controller.

My question is, what would be the easiest and most convenient way to test which part on the PCB is faulty? I have access to a multimeter and a soldering iron (not small enough to mess with the surface mount stuff, but good enough for some electrolytic cap removal etc.). Visually checked every part and found nothing unusual, and both the cap next to the working socket and non-working socket look identical, no bulging or cracks on top...

Any input on how to proceed would be greatly appreciated!

[selldoor]

Re: Benq v2210 Eco - one backlight strip not working

Pictures might be useful I have no knowledge regarding led back lights so it would help me learn. There are more and more coming on here now the guarantees have run out.

[martinlink]

Re: Benq v2210 Eco - one backlight strip not working






First one is a closeup of the backlight controller unit (green), second one is an overview of the whole power supply board.

On the closeup, the part on the bottom, which connects to the bottom header (white) is faulty. The connector above that works as it should.

I went to the local electronics shop and got a 10uF 100V cap, which is identical to the one on the small green board, and replaced it as it seemed like the most error-prone part (C522). This did not fix the issue.


What would be the next thing to try/test?


EDIT: Here's the service manual, page 27 and page 37 show the diagrams of the backlight controller board.

[selldoor]

Re: Benq v2210 Eco - one backlight strip not working

Thanks for the pictures
Service manual - always useful - bit I dont follow is it says clearly it is a LED panel then gives CCFL operating voltage and startup voltage,

I suppose the obvious things to check might be that you have Vin on Pin23
of the processor (you can test on R 507 if its easier to get at.

You could also test the Diodes D501 and D502 on the faulty side.

Also I can see a 0 rated resistor on the good side - if you can see the one on the bad side test as you would a fuse

[martinlink]

Re: Benq v2210 Eco - one backlight strip not working

I tested diodes D501 and D502, both show .301 and thus shouldbe fine.

I tested the 0 rated resistor (was behind the C522 capacitor so can't be seen on the picture), shows 0 resistance, so should be fine.

However, I am not sure how to test Vin. I found the pin23 on chip R502 (faulty side), and it conects to R522 (not R507, which should be on the working side?).
What mode do I select on the multimeter, what does it test and sould the device be running while conducting this test?

Thanks for the input so far!

[selldoor]

Re: Benq v2210 Eco - one backlight strip not working

Did you test the diodes with the leads reversed as well

You are correct R522 - scrolled too far up on the wiring diagram.
Set meter on next scale above 50vDC and try that. Board will have to be powered for voltage test .Black lead on a ground screw probe resistor with red - may as well do both sides of the resistor.

[martinlink]

Re: Benq v2210 Eco - one backlight strip not working

Testing the diodes in reverse gives no response (meter stays at 1) with both diodes.

Just double checking, red lead on pin 23 of the IC (or one of the connections on R522), black lead can be connected to the 0 (middle) pin on the power cord connector?
What should it show?

[selldoor]

Re: Benq v2210 Eco - one backlight strip not working

Diodes are OK 1 being overscale

I would prefer to use a ground on the board or pins3/4 on the long C513 cocnnector if you can get at them


Cap at C524 is rated for 25v so I would expect it to be less than that.

[martinlink]

Re: Benq v2210 Eco - one backlight strip not working

Tested it and it showed 17,3v on both sides of the R522 resistor.

[selldoor]

Re: Benq v2210 Eco - one backlight strip not working

Hmm - see page 39 backlight testing - suggests it should only be 5v!!

Perhaps do the same test on the good side?

Then continue with the other tests in that troubleshooter - not much point in my repeating them.


EDIT - You should also have the lamps plugged in while testing

[martinlink]

Re: Benq v2210 Eco - one backlight strip not working

Tested working side R507 to ground, also got 17,3v.
I read on page 37 about a 16v, which seems to be the closest to this one.
I'm measuring all voltages without having the backlights connected, otherwise I'd have to remove the backlights from the panel which is dangerous and difficult. Does that make a difference?


EDIT: Tested Pin24 (VREF), which should be 5v by the manual. When connecting C502 on the working side to ground, I get 5V. When I connect C527 to ground, it shows 17,3v again!! What might this mean? The IC chip IC502 is fried?

[selldoor]

Re: Benq v2210 Eco - one backlight strip not working

Perhaps without the lamps the voltages may be higher due to no load also isf there is any feedback mechanism it may think having no lights is a fault and shut down but I doubt that as it works with one string.

I dont know what it might mean - we are learning together I was hoping it was not the IC as I cant find one and I cant find a board either. This was as near as I got
- need to translate - put the link into google translate. Not that it tells us much
http://blog.sina.com.cn/s/blog_6a50b3930100mkgw.html

I am having an early night - perhaps some or our Us/Can members will comment.

[martinlink]

Re: Benq v2210 Eco - one backlight strip not working

Alright, thanks for your input so far. I'm calling it a day as well. Will check on the topic in the morning!

[budm]

Re: Benq v2210 Eco - one backlight strip not working

How many LED are there in each strip, from what I see in the diagram, there are 8 I-sense lines per socket, so each strip will have 8 set of LEDs.

[martinlink]

Re: Benq v2210 Eco - one backlight strip not working

I haven't disassembled the panel to access the LED strips so I don't know how many there are... Removing the metal housing around the panel involves removing the black tape that stops the light from leaking, and I don't have any to put on it after I remove it, so I really don't want to... (unless absolutely necessary).

[budm]

Re: Benq v2210 Eco - one backlight strip not working

Do not do that then, I am just curious since at 17V VDC, it means each string will have about 5 LEDs, 5LEDs x 8 = 40 LEDs per strip.
I believe this is how the circuit works (I did not look up the spec of the PWM IC yet)The VOUT is fed to the Anode of the LEDs strings (5 LED in series), the Cathode side is the return side that is connected to the Isense line (it is connected to the Drain pin of the MOSFET inside the IC and sensing resistor on the source pin then ground, there are 8 MOSFETs for 8 string). The MOSFET is driven on and off with PWM, the wider the pulse, the brighter the LED stings will be.
There is OVP pin which will shut down the circuit if the Vout is too high (such as over voltage from the power supply or no LEDs attach so the voltage will rise up high), you should check the OVP of the working and not working IC.

[Davi.p]

Re: Benq v2210 Eco - one backlight strip not working

I think that you may have a faulty segment of led and the easiest way to determine it is to connect the central pins Vout of the 2 output led connectors and detach the working led stripe from its connec., you may do this test also by disabling the protection of the faulty stage but since i cannot find the datasheet (the one posted by budm is not d.sheet) i can suppose the pinout and function is similar to for example a OZ9910 that i have on my hd, in this case it must be grounded one pin but actually i'm not sure which, maybe CMP but don't do it's risky, less risky is put LCT to gnd but i have to verify.

[budm]

Re: Benq v2210 Eco - one backlight strip not working

@davi: From post #1:
"I dismantled the monitor and tested the 2 LED backlight strips by connecting them to the 2 different sockets on the controller module (dunno how you call it).

I found that both the strips work when plugged into the top socket, and neither work when plugged into the bottom socket. So it seems that the problem lies somewhere in the LED controller."

[martinlink]

Re: Benq v2210 Eco - one backlight strip not working

Yes, the LED strips are confirmed working. I am 99% sure the problem is within one/some of the surface mount components of the green board. It's just that I have no knowledge of how to identify the faulty component(s)... other than desoldering them one by one and testing them out of circuit, but that's a full week of work for me.

[Davi.p]

Re: Benq v2210 Eco - one backlight strip not working

I have forgot it... from the picture i don't see the switching mosfets, there is only a place for them, i don't know how the boost converter can work without..