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

Ok, thanks for the guidance Momaka!

[momaka]

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

Yes, these inverters are powered by a DC input. Essentially they are made so that you can directly connect them to the existing power supply in the LCD monitor and completely replace the original inverter. If you look around, some of those inverters even have dimming control (so your logic board can control the backlight brightness), in addition to having an On/Off signal.

As to which one to get...
For testing, I recommend either only the 1 or 2-tube inverter - that way, you should be able to isolate which CCFL tube or assembly is having issues.
For full inverter replacement, the 4-tube inverter should be able to acomodate most monitors. Just keep in mind that there are different inverter designs on eBay: some might have the CCFL connectors in awkward spots that may not allow you to easily connect your CCFLs. In addition to that, the PCB sizes of different designs can vary a little - so depending on how much space you have in your monitor, you might need to get a specific size to make things fit.

Regarding the monitor that has only one connector on the top and bottom...
Are the wires going to each CCFL very thick, or is one thin and the other one thick? The former could indicate that there are two CCFLs in series for the top and the same for the bottom. I think those assemblies usually require an inverter that runs at a higher voltage. I've only seen it a few times though.
However, if each CCFL assembly has one thick and one thin wire (the latter case above), then you probably have a monitor with only two CCFLs total. If that's the case, then you can test that only with the 2-tube CCFL inverter.

Funny, the third one does not ship to Canada?

No worries. There are 10s (if not 100's) of sellers for these things on eBay and Ali Express. So if you search around, you should be able to find a seller that ships to you. I just picked the first (cheapest) inverter that appeared on eBay for each type and posted it here. Mine cost me $5 when I got it a few years back. So if you look at the more expensive ones, you should be able to find one that ships to Canada.

[rddube]

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

Thanks Momaka for this info. I am certainly going to look into getting one of these.

A question come to mind however, how are they powered not AC ? Is it simply putting 5V - 28V DC input?

Funny, the third one does not ship to Canada?

Also, which one should I get...my former repair the cfl's had 2 connectors each, whereas the one I am working on now, there is only one connector top and bottom?

Tks again!

[momaka]

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

It only took us 12 pages. I commend you for sticking with it.

Well, I have to say, I commend you ALL for being so patient and persistent... and it looks like it paid off in the end - you got the inverter working.

Maybe we should go to the lamp route, and use Budm's method with one of the F13TT lamps I have. I could plug it into the CN801 and see if the lamps go out?

What do you think?

It's definitely something you should consider trying in the future if you want to save time. Of course, you probably wouldn't have learned as much from that endeavor as much as you did from this one.

That said, if you do plan to do more monitor repairs in the future, eBay and AliExpress also have cheap 1, 2 and 4-lamp pre-built inverters. These can be very handy if you want to test lamps. Here are a few examples:

https://www.ebay.com/itm/1pc-5-28V-1.../173002933466?

https://www.ebay.com/itm/2-Lamp-Back.../182959252359?

https://www.ebay.com/itm/Universal-1.../263014692288?

For $3-5 each, these inverters are pretty much a must-have for anyone that works on LCD monitors. Either that, or get some LED kits and retrofit the monitor with LED backlights. Of course that's easier said than done. Mostly due having to open the LCD. Speaking of which:

You can only open that panel, it's not hard but tedious. Changing the cfl desoldering the old and resoldering the new in the manner that fits inside the panel instead is a pain in the arse...

+10000000000
I did a CCFL replacement on a 22" HP, and to say that it was a pain in the butt is an understatement - it's lots of trial and error and cutting and trimming and refitting until everything can be closed back up. And on top of that, if you're not careful and don't have a very clean work area, those polarizing sheets in the LCD will pick up all sorts of dust, dirt, and linens - essentially really making the repair ugly if not careful. Luckily, I've read about other people making that mistake, so I was extremely careful and it all turned out okay. But it's definitely something I don't want to do again, if it can be avoided.

[rddube]

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

This thread continues here:

https://www.badcaps.net/forum/showthread.php?t=67285

[rddube]

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

I think I will leave them for now and start a new thread for the main board. See you in a few!

[will62]

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

Flickering is not good. Like I mentioned a page or so back, what are the odds that both boards would fail for different reasons at the same time? The flickering could be related to not having the correct inputs on the jumpers. As long as the lamps are coming on, I'd leave it until you see what happens with good main board inputs. The flickering means that something is not happy, so I wouldn't leave them on for long periods, as I recommended above.

If you're feeling adventurous, I guess you could go back and change each thing back to what it was until you hit which one was causing the lamps not to come on. Then you could zone in on that one cause and try to eliminate the flicker. (BRT_ADJ, POWER sav, capacitor)

[rddube]

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

Ooops, I checked if they were on, and they stay on (looking through the back near the wires going to the CFL), but when I looked at the screen they are flickering....could it just be resistor values on the jumpers?

When I turn on AC they come on bright and then within a fraction of a second start to flicker, constant regular flicker?

As far is sticking with it, you Will are the main reason why I did, you have been so patient and I have learnt so much, I have to really thank you for it. And yes, am I ready for the main board!

But do I do any more tests to get rid of that flickering?

[will62]

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

It only took us 12 pages. I commend you for sticking with it. We took the long way around to find out that there was no problem with the board, but hopefully you learned a lot about the inverter section. Don't need any measurements, just leave lights on for a good while to make sure they stay on.

Now that we've finished the "easy" part, you ready to get to the main board?
This thread got so long, you should probably start a new one for part II - main board. I guess you could put links in both.

[rddube]

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

Eureka! It works. With the blue wire with 1K resistor into 3.3V and the BRT_ADJ wire with 10K resistor in 3.3V (I changed from 5V to 3.3V), with Frankie in C817 the lights come on and stay on!!!

I am so excited that I didn't take any voltage measurements because it works!

Ok, so do you want me to take measurements or do we go to the main board now and try and get that thing to run? Tks guys!

[rddube]

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

ok, I will rebuild Frankie and test with the CFL's plugged in. Will report later.

Thank you for your help and patience!

[will62]

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

453 ohms is ok for the secondary. Good catch on Dumah for recognizing the cause. I wouldn't put ole crispy back in there. I believe that cap and the inductance of the secondary form a tank circuit. It's value determines the resonant frequency of the circuit. That's the point that the max power can be absorbed for hitting striking voltage. If you increase the cap value, you lower the resonant frequency. The opposite for lowering cap value. It's over my head to tell you how a 2pf difference would impact lighting the lamps. Better rebuild Frankie, or we'll be wondering about it down the line.

[rddube]

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

Will: Ok, that is what I had, the 1K resistor connected from 3.3V to blue.

Dumah: Yes I did power it on without the CFL's just wanting to check what voltage I was getting on the blue wire. I shouldn't...I thought that the power to the CFL's was turned off when they are not connected?

Not sure what to do now. I removed the C817 and checked the resistance between 7 and 8 of the secondary and I get 453 ohms, just like before. That capacitor (charred) still measures 12pf. I inspected all my soldering, the last thing I had done was to put down the top pin of the diode and solder it and don't notice anything special. I have some 5 pf HV caps, and one of them measures 14pf (if my transistor tester is accurate). Should I put that one in place of C817, or the old 10PF that I still have, or the Frankenstein cap that I had made but dismantled?

[Dumah Brazorf]

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

You're not powering the board without always connecting the ccfls, don't you?

[will62]

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

I was talking about 1k from 3.3V to blue power saving. I can't find anything that says what the normal signal to power saving should be. Looks like your original jumpers had 5V going to it. Just move it over to 3.3V (orange). You can try powering on with and w/o the jumper to power saving.

I believe Dumah was talking about using a 10k resistor to lower the voltage going to BRT_ADJ. We need to get that voltage down to around 1.5-2.5V to see if that changes anything. If necessary, use the resistor divider I mentioned above

On post 215:
That's not good. C817 goes between the pins on the transformer secondary. I would remove it and check resistance between 7 and 8 on the secondary. Also check for shorts to ground. What could have caused that?

[rddube]

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

Oh, oh, things are getting weirder. I decided to switch the blue wire on to 3.3V with the 1K resistor and try it out.

Before making the test, I measured voltage on the blue pin with board upside down...I got 3.228V. While I was doing that I was hearing like a very faint crackling noise so started to investigate what it could be. Then after a few seconds I saw a bit of smoke coming from under the board (the top side) so I unplugged everything.

Turned the board around to inspect it and this is what I found. C817 had started to roast (see picture).

I haven't touched anything, just measured resistance at C817 and I get approx. 450ohms like before.

What's going on?

[rddube]

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

Will, 2 things. Do you mean the 1K resistor or the 10K resistor on 3.3V?

Also, in the diagram you just attached (which is right on with my connector) we have a 1K resistor on the power saving mode (pin 5)...should I remove that, maybe that is causing us the headaches, no?

[will62]

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

I think the connector is like the one in the pic. BRT_ADJ would be pin 1. Jump the 1k from blue to 3.3V

[rddube]

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

Ok, I noticed that we have 3 resistors one on the blue, one on the green and on the white all with 5 volts. Not too sure what wire is the dimming is it the blue? The green would be enable and what is the white?

I think Will you said pin 7 is the dimming, so I am trying to trace pin 7 back to the connector but I get lost along the way?

I resoldered the diode and made a 10K resistor jumper, so I am ready to go, but want to do it the right way. Do I replace the 1K resistor on the blue wire with the 10K?

[will62]

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

Yeah, try what Dumah said and see what the voltage goes down to. If that doesn't get it down, we'll use a resistor divider. Solder 2 equal resistors (value doesn't matter, just over 1k) soldered end to end. Another resistor of value several hundred to 1k soldered at the junction of the other 2, making a "T".

One end of the equals to ground, other end to 5V. The resistor in the middle to dimming. That will cut your voltage in half. Try it at 5V and 3.3V.

It's possible that the MP10091 is getting that oscillation for burst dimming from somewhere else. The problem is that we only have the datasheet for the MP1009. We know the pinout has changed, and we're left guessing what else has changed.

The only common connection between the main board and the inverter section, are the enable and dimming lines. I guess a short on the main could have zapped the driver chip via those lines, but the chip seems to be working. Otherwise, you had 2 random failures on 2 different boards at the same time.