Acer x223w first white screen, now no backlight

[teri3s]

Yesterday, monitor was in use for a few hours then screen just turned white. I could still see a bit of the video I was playing showing through. Tried unplugging power, plugged back in...same issue. Screen was a messy white and grey.

When I turned it on, it would come on, with blue led "on light" on keyboard, switch to amber with screen going black, then back on with the messy white.

Took monitor apart, disconnected input board, plugged back in a few times, turned on, and screen was completely white as though the backlight was up to maximum intensity. Started checking the voltages, they seemed alright. Turned monitor on again later after combing online for similar issues. Backlight no longer came on, couldn't see anything on screen.

At present I get no voltage readings from inverter side of board.

I am a novice when it comes to the intricacies of component testing, so any advice is appreciated.

Edit: right now when hook everything up, and turn it on, the led goes from amber to blue and stays blue.

[retiredcaps]

Re: Acer x223w first white screen, now no backlight

Started checking the voltages, they seemed alright.

1) Excellent photos. It helps a lot in troubleshooting.

2) On CN801, what are the voltages for all the pins?

3) On the logic board, there is a voltage regulator at U106. What are the voltages for all 3 pins with respect to ground?

4) Check picofuse F802 (yellow fuse near top of board on the inverter side). A good fuse should measure less than 1.0 ohms.

[teri3s]

Re: Acer x223w first white screen, now no backlight

Thank you retiredcaps, I was a bit nervous about the pics had to retake them and then started worrying about the long shadows.

I just noticed that when I touch the black lead to ground and the red lead to the heatsink next to CN801, the voltmeter is reading minus 75V. The other heatsink registers no voltage.

2) CN801
1. VCC 5V (reads 5V)
2. VCC 5V (reads 5V)
3. GND
4. GND
remaining 4 pins (in order, on/off, Brightness, Vol, Mute) read zero volts.

3) U106 (Logic Board)

Pin 1 reads 0 volts
Pin 2 reads 3.2 volts
Pin 3 reads 4.7 volts

4) F802 (Inverter Side of PSU)
Reads below 1.0 ohms (using a DMM and an analog)

[retiredcaps]

Re: Acer x223w first white screen, now no backlight

I just noticed that when I touch the black lead to ground and the red lead to the heatsink next to CN801, the voltmeter is reading minus 75V.

I believe that heatsink is "live". It is attached to the power mosfet. I'm guessing your ground was probably on the cold side, that is why you get -75V reading.

Do you get any DC voltage reading across F802? If yes, what is it?

[teri3s]

Re: Acer x223w first white screen, now no backlight

Across F802 I get +5V
The jumper above, "J808" I get +17.6V

[retiredcaps]

Re: Acer x223w first white screen, now no backlight

U501 and U502 are n channel mosfets. Thanks to the excellent photo, I can read the part number. The datasheet is at

http://pdf1.alldatasheet.com/datashe.../AP9971GD.html

Check for shorts between S1-D1, S1-G1, and D1-G1. Do the same for the "2"'s. See the datasheet for the proper pin orientation.

Any resistance reading below 30 ohms suggest it may be shorted. Report all readings.

[teri3s]

Re: Acer x223w first white screen, now no backlight

Alright retiredcaps, will do. Also, a sincere thank you for all the help thus far.

[pedro]

Re: Acer x223w first white screen, now no backlight

Across F802 I get +5V
The jumper above, "J808" I get +17.6V

Did you really mean "across F802"? If so, that's a problem ...

[teri3s]

Re: Acer x223w first white screen, now no backlight

Not sure what you mean pedro?

[teri3s]

Re: Acer x223w first white screen, now no backlight

I am not sure what I'm looking for exactly in terms of ohmmeter readings while checking for shorts so I'll just post what I found and if I say anything stupid.......well please bear with me lol.

Am I supposed to desolder these devices to test them?

But in the meantime, using an analog meter, when I touch the probes to S1 and D1 it goes from near 0ohms and then gradually falls back to infinite ohms.

D1 and G1 it goes from about 50 ohms and the needle falls back to infinite resistance.

S1 and G1, the needle stays at about 50 ohms (or the middle of the scale).

This goes for both mosfets.

When the power button is off, I get 17.7V at U501 and U502.
When the power button is on, I get 18.0V at U501 and U502.

[PlainBill]

Re: Acer x223w first white screen, now no backlight

Not sure what you mean pedro?

This may be a communication problem. When I hear 'Across F802 I get +5V', I interpret it to mean that you put one probe on one end of F802, the other probe on the other end of F802, and read 5 volts. The only way that can occur is if F802 is open. And that is a problem, because when a fuse goes open it is usually because something has failed (shorted).

PlainBill

[teri3s]

Re: Acer x223w first white screen, now no backlight

Thanks for that PlainBill. Yeah, I got an inkling that "across" would cause confusion.

The picofuse is not open. It reads nearly 0 ohms when the probes are placed at opposite ends. No voltage registers if probed "across".

If I go from a ground point to the picofuse I get the 5V reading.

[PlainBill]

Re: Acer x223w first white screen, now no backlight

Thanks for that PlainBill. Yeah, I got an inkling that "across" would cause confusion.

The picofuse is not open. It reads nearly 0 ohms when the probes are placed at opposite ends. No voltage registers if probed "across".

If I go from a ground point to the picofuse I get the 5V reading.

Yeah, that makes more sense. It's a nasty area, because when I see 'At the fuse' I wonder 'which side of the fuse?'

PlainBill

[retiredcaps]

Re: Acer x223w first white screen, now no backlight

Am I supposed to desolder these devices to test them?

Generally in order to get an accurate reading, yes. However, I usually test "in circuit" first and if the readings suggest a short, then I desolder to verify.

S1 and G1, the needle stays at about 50 ohms (or the middle of the scale).

What about the "2"s? S2-D2, S2-G2, D2-G2?

On the analog meter, what scale is your dial set to? 1x? 10x?

[teri3s]

Re: Acer x223w first white screen, now no backlight

Scale was set to 10x

The "2's" displayed the same pattern.

[retiredcaps]

Re: Acer x223w first white screen, now no backlight

Hmm, I wondering about the 50 ohms and wonder if it could be shorted? If you can, desolder the chip and retest out of circuit.

Before you do that, please measure the resistance between the yellow dots and the red dots. Report both.

You are measuring the resistance of the inverter transformer secondaries. Do this with power off. I don't need any voltage readings from this area.

[teri3s]

Re: Acer x223w first white screen, now no backlight

With Rx10 setting on analog, about 500 ohms at both the red and yellow dots.

[retiredcaps]

Re: Acer x223w first white screen, now no backlight

With Rx10 setting on analog, about 500 ohms at both the red and yellow dots.

Both those readings look good.

The 50 ohm reading is still suspicious to me. You may want to desolder and retest them just to be sure.

[alexanna]

Re: Acer x223w first white screen, now no backlight

remaining 4 pins (in order, on/off, Brightness, Vol, Mute) read zero volts.

)

It looks like there may be a voltage missing on the signal card, for the backlights to come on the great majority of monitors there will be around 3 volts on the backlight on pin.

[retiredcaps]

Re: Acer x223w first white screen, now no backlight

It looks like there may be a voltage missing on the signal card, for the backlights to come on the great majority of monitors there will be around 3 volts on the backlight on pin.

Good catch. I totally missed that.