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

[rddube]

Hello everyone,

I so much enjoyed my last post that I bought this non working Benq G2255 monitor that when plugged in the power light lights up as amber and no matter what I press, I get no response.

Included are photos of the boards.

I checked the voltage on the big cap 164V, and I get 3.3V and 5.2 V on the connector from the power board to the control board.

Power supply looks good, the caps look OK although not the best brand (Elite), so I am eager to have your thoughts on what I should look at next.

Many thanks to all of you!

[rddube]

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

Here are some better photos of my boards taken in daylight.

Any ideas?

Tks,

Ray

[Dumah Brazorf]

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

Did you check the power button?
Maybe eeprom issue.

[rddube]

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

Did you check the power button?
Maybe eeprom issue.

Hello Dumah,

Thank you for your reply. What do you mean by checking the power button? If eeprom issue, how can I fix it?

I did plug in the power board and main board only, and the amber light comes on. Checked the voltages on the voltage regulator at top of photo 5 of my second post with photos, and I get 3.3V on left leg, and 1.8V on right leg, so that looks ok.

Then I checked the 2 caps on that same board, removed them and they test ok. Resistance at cap legs when installed and removed is 85ohms...does that look normal?

Many thanks for your input!

[Dumah Brazorf]

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

I mean to check that the actual power button has 3,3V or whatever at one end and when pressed that voltage goes to zero.

[rddube]

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

Thanks Dumah...didn't know that is the way it works. Will check it immediately and advise.

[rddube]

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

Ok, checked the power button and I get 1.5V and when pressed it goes to 0. Is 1.5 enough?

I measured the 5V and 3.3V and I get 4.9V and 2.79-80V. Do you think it could those voltages that are too low? The 3.3V is produced by a regulator on the power supply board marked 61-33 1145DG? Could it be faulty?

Tks!

[Dumah Brazorf]

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

Yes 3,3v seems too low. Measure it with the mainboard disconnected.

[rddube]

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

Ok, checked the power button and I get 1.5V and when pressed it goes to 0. Is 1.5 enough?

I measured the 5V and 3.3V and I get 4.9V and 2.79-80V. Do you think it could those voltages that are too low? The 3.3V is produced by a regulator on the power supply board marked 61-33 1145DG? Could it be faulty?

Tks!

Ok readid those measures with and without the main board attached...my mistake in quote above for the 3.3V, sorry:

with without
Orange 1 3.25V 3.28V
Orange 2 3.25V 3.28V
Red 1 5.00V 5.01V
Red 2 5.00V 5.01V
Blue 0.774V 0V
Black 1 0V 0V (must be ground)
Black 2 same readings as black 1
Green 0V 0V
White 0.882V 0.557V

Also took the reading on the 61-33 1145DG regulator and some of the transistors on the power board, while not connected to the main board. Attached is an annotated picture with results. Also took a reading before and after a zener diode for reference.

[rddube]

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

I should have mentionned that the 0.04V on the right side of the zener diode goes to the blue wire, which reads 0.774V connected to main board and 0V when not connected. That seems strange, as if the blue wire was returning a too low voltage from the mainboard? I'm a bit confused.

Attached is a copy of the datasheet for the Shunt regulatorTL431.

Unfortunately I can't find a schematic for this power supply 4h.1ld02.a40

[Dumah Brazorf]

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

Unfortunately i don't have any clue.
Here the firmware i found: http://www.kenotrontv.ru/forum/files...benq-gl2250-b/

[budm]

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

"with without
Orange 1 3.25V 3.28V
Orange 2 3.25V 3.28V
Red 1 5.00V 5.01V
Red 2 5.00V 5.01V
Blue 0.774V 0V
Black 1 0V 0V (must be ground)
Black 2 same readings as black 1
Green 0V 0V
White 0.882V 0.557V"
At this point the problem looks to be on the main board.
Does the Blue 0.774V 0V change state when power switch is toggle on and off?
Does the White 0.882V 0.557V" change state when power switch is toggle on and off?
Those two wires look to be for the BL-ON and Dimming control signals from the main board.
You can easily verify if the power supply/inverter board and backlights are good or not by running the power supply board by itself with 1K 1/4W resistor connected between Blue wire pin and 5V, and another 1K 1/4W resistor between White wire pin and 5V. The backlights should come on and stay on the minute you apply main AC to the board.

[rddube]

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

Oh Budm, thank you so much for stepping in. I will do those tests and report back very shortly. Thanks again a million!!

[rddube]

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

"with without
Orange 1 3.25V 3.28V
Orange 2 3.25V 3.28V
Red 1 5.00V 5.01V
Red 2 5.00V 5.01V
Blue 0.774V 0V
Black 1 0V 0V (must be ground)
Black 2 same readings as black 1
Green 0V 0V
White 0.882V 0.557V"
At this point the problem looks to be on the main board.
Does the Blue 0.774V 0V change state when power switch is toggle on and off?
Does the White 0.882V 0.557V" change state when power switch is toggle on and off?
Those two wires look to be for the BL-ON and Dimming control signals from the main board.
You can easily verify if the power supply/inverter board and backlights are good or not by running the power supply board by itself with 1K 1/4W resistor connected between Blue wire pin and 5V, and another 1K 1/4W resistor between White wire pin and 5V. The backlights should come on and stay on the minute you apply main AC to the board.

Ok, so tried these tests and here are the results:

The blue and white wires (0.774V and 0.882V) don't change when I hit the power button. They stay the same.

Tried the power supply/inverter board (without main board) with backlights connected and 1K 1/4W resistor connected between blue wire and 5V and another (same value) between white wire pin and 5V and when applied AC to board, nothing happened - no backlights.

Between inverter transformer out pins, I get 450 ohms resistance same as C 817 as shown in the attached photo.

[budm]

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

So for sure that you have problem on the main board some where since those signals should toggle.
So the backlights lamps did not even flash for seconds? If that is the case then you also have power supply problem.

[rddube]

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

So for sure that you have problem on the main board some where since those signals should toggle.

But the main board was not connected when I did the test with the 1K resistors, was it supposed to be connected? I just had the power supply / inverter board connected to the backlights with the 1K resistors from blue to 5V and from white to 5V...so how could the main board be in cause?

So the backlights lamps did not even flash for seconds? If that is the case then you also have power supply problem.

No, nothing no reaction at all??

So with my first comment (main board not connected during test), could it mean that it is only the power supply that has a problem? If, what should I look for, voltages seem to be OK - 3.3V is a little low at 3.28 however. I did remove all electrolytic caps (except main one) and checked them with my ESR meter and they all measure fine. Not too sure where to look next?

[rddube]

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

Found this service manual which seems to use the same power board and main board (version without audio) of this monitor. Might help in diagnosing?

The connector CN701 is slightly different (this one has 12 pins and mine has 10 pins) but it might be audio related?

Anyhow, any help is welcome!

Tks!

[Dumah Brazorf]

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

I think green is bl_enable pin and blue could be the PWR_SAV signal, so try with resistors on this 2.

[budm]

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

But the main board was not connected when I did the test with the 1K resistors, was it supposed to be connected? I just had the power supply / inverter board connected to the backlights with the 1K resistors from blue to 5V and from white to 5V...so how could the main board be in cause?

No, nothing no reaction at all??

So with my first comment (main board not connected during test), could it mean that it is only the power supply that has a problem? If, what should I look for, voltages seem to be OK - 3.3V is a little low at 3.28 however. I did remove all electrolytic caps (except main one) and checked them with my ESR meter and they all measure fine. Not too sure where to look next?

We use the resistors to simulate the control signals of the main board, this is how you test the power supply board by itself.

[rddube]

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

I think green is bl_enable pin and blue could be the PWR_SAV signal, so try with resistors on this 2.

Ok, so tried this combination and still nothing.

I noticed that there seems to be heat marks under the power board - I tried taking a photo so that it is visible, and I circled where these heat marks are in case that might spring some ideas.