Benq G2255 doesn't power on - amber power light when plugged in

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Will, this pinout seems to be the one of the MP10091ES, taken from a Philips service manual attached. The critical components for IC801 is an MP10091ES.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Ok, here are the readings for pins 1, 2, 4 and 16 (I also jotted down the frequency):

Frequency Min Max PP

Pin1: 59.19Khz -37.58V 5.23V 42.52V
Pin2: 71.49Khz -37.58V 6.64V 44.23V
Pin3: 71.036Khz -37.58V 7.85V 45.44V
Pin16: 71.78Khz -37.58V 3.22V 42.81V

Hope these make sense. I put power on and as quickly as possible pressed the hold button on the scope.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Good job on the pics and video. Those voltages (min,max,pp) are all over the place, and not following the lamps to different connections. The waves also don't look like what is expected based on the datasheet (pic on post#114). Note that the "LI" waves center on 0V and the "OV" waves center on 6V. Keep in mind that we don't have the datasheet for MP10091ES. I am looking at the datasheet for MP1009. I have seen specs that refer to the 10091 as being from the 1009 series, but we already know they have different pin-outs, and they probably also have different internal parameters.

I wonder if some of the wave changes are related to when they were measured. We know that the chip is seeing something that it doesn't like in the first couple of seconds. Just to be sure, Can you please redo the tests, but start each test from power being off. Try to press hold as quickly as possible on each test. No need to take new pics, just give me min, max & pp for each pin at startup. If pin 16 is doing what you show in the video, I don't doubt that it is causing the shutdown. There's a couple of ways to check that, and we'll try those next.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

ok, redid all the tests CFL's inverted and CFL's in their original position and here are the photos of the scope.

I noticed pin 16 was changing frequency quite a bit, so I took a little video (hope it's ok to post it here, if not I will remove it no problem - had to put it in a zip file because the extension is not allowed) to show the movement of the wave.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Ok, found my problem with the waves jumping...this oscilloscope has alligator clips so the ground is fine, but the probing wand I had to make out of a copper wire (solid) and I was holding the wire instead of the plastic covering the alligator clip, creating disturbance I guess.

Here are the real pins 1, 2, 3 and 16, with the CFL's connected as original. I noticed that I have a hold function on the oscilloscope so I used it to take the pictures, hope that's ok.

Will get to redo pin 1 with other setup, will rename the photos and reupload everything including a photo of the whole board with light under, right after lunch.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Well, I posted some things to check next, before reading your comment above. I've edited all out except asking for a new pic. Hopefully you get some stable waves with lamps swapped. If not, go back to original setup and probe pin 1. I think that's all we're missing. Rename pics with correct pin #'s.

Can you take a complete pic with light under the board, similar to the ones you put up earlier?

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Ok, here is the first tests.



Dumah, you are going to see what I get on pin 1 and 16 in the photos.

For Will:

Lights come on nice and solid, no flickering no tint, just white light top and bottom.

First I show you my setup, so you can admire

Next are the photos for pin 1, then pin 2, 3 and 16 respectively. 1, 2 and 16 look smooth, but pin 3 is pretty spiky. I took 2 photos of pin 3 so you could see the amplitude, especially on photo 2.

So what next, do I next, do I flip the board and do the tests, or is there something wrong with pin 3?

Tks a million!

Sorry gentlement, while setting up to do the test with the CFL's plugged in the opposite sockets, I realized that the tests above were done on pins 2, 3, 4 and 16...not pin 1. So the photos are for pins 2, 3 and 4 instead of 1, 2, 3.

I tried repeating the test this time with the CFL's the other way, this time on the right 1, 2, 3, pins, but for some reason my oscilloscope doesn't show me a stable sine wave, it jumps all over the screen - same thing for all 3 pins. There must be something I am doing wrong? The CFL's light up as before however. Will try again and see what gives. Sorry for the error in the previous post.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Swap the lamps. If pin2 became spiky and pin3 smooth there's something wrong with a lamp.

Ok Dumah, will do the tests this afternoon as I have to flip around and reinstall my alligator clip on C803 to short pin 5. Right now I have to go get my grand daughters to bring them to Toys'r us, order from my wife!

Will probably wait for Will's advice too. Since pin 3 is current feedback for one of the lamps, could it not be a component on the line from the lamp to pin 3 that could be causing this? We'll know for sure once I do the test.

Thanks for your advice.

[Dumah Brazorf]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Swap the lamps. If pin2 became spiky and pin3 smooth there's something wrong with a lamp.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Ok, here is the first tests.

What measure pin 1 and 16 in this case?

Dumah, you are going to see what I get on pin 1 and 16 in the photos.

For Will:

Lights come on nice and solid, no flickering no tint, just white light top and bottom.

First I show you my setup, so you can admire

Next are the photos for pin 1, then pin 2, 3 and 16 respectively. 1, 2 and 16 look smooth, but pin 3 is pretty spiky. I took 2 photos of pin 3 so you could see the amplitude, especially on photo 2.

So what next, do I next, do I flip the board and do the tests, or is there something wrong with pin 3?

Tks a million!

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Oops. Forgot to mention, scope on AC.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Hey, that little $20 scope is not a bad one to learn on, is it? It looks like it'll do everything we need on the power board.

Did you notice if both lights came on equally? No flashing or anything? Jump pin 5, turn off the light in the room, then power up the board. Notice any difference on how each lamp starts up (blinks, pinkish hue... etc).

Go ahead and run the tests on pins 16, 1, 2, & 3. We need to narrow down which connector circuit is causing the problem. Then we'll swap lamp connectors, rerun the test and see if the problem moves.

[Dumah Brazorf]

Re: Benq G2255 doesn't power on - amber power light when plugged in

What measure pin 1 and 16 in this case?

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Ok, Will this is so exciting...as I was getting prepared to do my tests, pin 5 to ground, etc. I did a quick test to see if the CFL would light up. Well guess what, they did and stayed light as long as I kept the AC on. But I didn't leave it for too long just in case. I removed the alligator clip that grounds pin 5, powered up and the CFL's came on, but out after about 2 seconds.

I have to admit that the opening to see the CFL's is very small so I might have overlooked it before.

So I put the alligator clip back on C803, put power on and they lit up and stayed lit for at least 10-15 seconds...then I powered down.

I took the attached picture of my oscilloscope on pin 14 for you to see...sorry for the quality, but one hand on the probe, the other putting power on and having to grab my camera etc. You can't see the frequency because it sort of flashes on and off, and I guess the photo snapped while it was off, but it ranges in the vincinity of 71-72Khz.

So is this good news?

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Pin 5 remains shorted to ground.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Will do I leave the shorted pins on the IC for those tests?

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Refer back to the MP10091 diagram pic on post #104. You're going to be probing pins 16, 1, 2 & 3 next. Remember to find a near component to put
the probe on. Easy to slip while you're watching the scope (pin 16 is next to ground pin). Look at the attached pic and you'll see what we're looking for.
Pay close attention to the thresholds noted on the pic. Whether or not the wave stays above or goes below the threshold is the fault trigger. Since neither of the bulbs came on, I have a feeling that I know where this is going, but let's see what your waves look like. Since the bulbs are not on, running beyond 5 seconds on fault bypass is probably not a problem.

As for your question about the scope setting, leave it on DC for these tests. After these tests, why don't you watch a couple of videos on checking for voltage ripple with a scope. If you set the scope on AC, you'll only see the ripple component. See if you can estimate peak to peak ripple on your 3.3V, 5V and 20V supplies. Some datasheets will specify a maximum tolerated ripple.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Regarding the logic board issue...
Try connecting only the logic board to the power supply and the power button board. Leave the T-con board disconnected. Does the power LED still stay orange only and is the monitor still not responsive?

Hey Momaka, nice to see your sound advice in my thread! Yes it stays orange and no response.

If yes, try supplying 5V and 3.3V to the monitor from a computer ATX PSU - this will eliminate noise/ripple problems from the monitor's PSU, if there are any. If the logic board is still not responsive, then the issue is probably either a firmware one (bad flash chip / firmware corruption) or the main chip on the logic board. The only other thing I can think of is that 85-Ohm resistance you measured - that could be a partially-shorted ceramic capacitor or diode/transistor. Is this resistance on the 1.8V line or the 3.3V line? The former is a bit more worrisome.

Ok, will try to do that once I get the power board off the bench, because right now it is connected with the oscillscope, and I will have to dismantle one of my PC's to get the ATX PSU. For your other question, it is on the 3.3V line....shucks!

At this point, it clearly isn't economically worthwhile to repair the monitor. But the knowledge you learn from the troubleshooting process might be - so that alone could make the repair worthwhile overall. It really depends what you are trying to get out of this.

You are right, I am really enjoying getting guidance from Will62 and am learning a lot along the way. I love it!

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

The conical shape may be something related to MPS's Nu-Pulse technology, not sure.
Now we're going to bypass the chip's fault protection and take a longer look at the TG and BG signals (same as earlier). Need to jump pin 5 to ground. An alligator clip across C803 should work, if it'll hold. After the clip is on, measure resistance between pin 5 and pin 15. Should be near 0 ohms. Run the test for about 5 seconds to get a better look at the waves. Don't want to run it too long because shutdown may be due to over-current. See if you can display the frequency on your scope.

Thanks Will62 for being so kind in spending your time on my case. It is really appreciated and the knowledge that I gain is priceless. Thank you very very much!

Ok, it worked and the waves stay on.didn't go over 5 seconds on either pin. Get a conical wave and the frequency is 71.2Khz on both pins.

Questions
1. Do you have a hole on the back of that panel so you could see the backlight if it came on? If not maybe you could see some glow at the corners where the cables go.

Yes I do have some areas where I would see the lights glow, but nothing comes on.

2. Does your DMM have frequency function? If so, you could try touching the top of the transformer (not the pins, just the top plastic) with your red probe (black to ground) while you are running the mosfets, to see if you pick up the oscillation frequency.

Yes it does, but the board is upside down, so not too sure if I should poke my probe under the board and not see if I am touching metal or plastic, so I skipped this. But I did try to put my probe (black to ground) on the pcb where the transformer is and turned it on briefly, but no reading on my meter.

3. Did you check your probe on the scopes 1kHz signal? There's a loop at the top of the scope to hook on to. Pulse nice and square, or conical? (set horizontal to 1 ms).

Yes, I get a nice square wave but have to go to 50us....my tests with the pins were at 10us, because at 50us the wave is sort of flat. I did notice during the tests that the voltage range was between 12 and 13V.

Will, one question I forgot to ask...on the oscilloscope I have GND, AC and DC settings. I set it to DC settings for the tests, is that OK?

[momaka]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Regarding the logic board issue...
Try connecting only the logic board to the power supply and the power button board. Leave the T-con board disconnected. Does the power LED still stay orange only and is the monitor still not responsive? If yes, try supplying 5V and 3.3V to the monitor from a computer ATX PSU - this will eliminate noise/ripple problems from the monitor's PSU, if there are any. If the logic board is still not responsive, then the issue is probably either a firmware one (bad flash chip / firmware corruption) or the main chip on the logic board. The only other thing I can think of is that 85-Ohm resistance you measured - that could be a partially-shorted ceramic capacitor or diode/transistor. Is this resistance on the 1.8V line or the 3.3V line? The former is a bit more worrisome.

We are trying to get the inverter working, but I also have a problem with the logic board, so down the end, it might not be economically viable to repair this monitor? What do you think?

At this point, it clearly isn't economically worthwhile to repair the monitor. But the knowledge you learn from the troubleshooting process might be - so that alone could make the repair worthwhile overall. It really depends what you are trying to get out of this.

I agree that we need to get the logic board working first. Without it, the monitor is as good as dead anyways.

The one I find suspect is blue and written:
8
3KV
SEC
Not sure what I should get as I don't see 8pf 3KV capacitors on digikey?

It's probably an 8.2 pF capacitor (as that's a standard value).