Acer X241W (Power Board Failure)

[stevekasian]

Hi,

I have an Acer X241W with a backlight failing to come on.

Display works - I can see the OSD Menu when holding a flashlight to the screen, and it is responsive to menu/button controls.

Upon opening up the unit, I could tell it has been worked on. Replacement low ESR caps have been installed on both the power and logic boards, and the work looks good.

I pulled the inverter board and checked the transformers. They all appear to be in working order. No burns or heat marks visible and each measures the same resistance across each lead in each respective combination.

So I decided to power up the power board (Model AS08B360411) and take some readings from the 5v/12v/19v rail that powers the inverter. When switching the unit on and measuring voltages before the standby mode engages, this is what I came up with (see attached images and annotation on image #3).

There does appear to be heat discoloration on the front and back of the section of the board I'm dealing with, although I believe it is probably from an earlier failure, as no components appear to be damaged/burned.

Anyone care to help me troubleshoot this board?

Thanks,
SK

p.s. Entry #17 on the following page reports almost the same readings on the pins of a similar monitor: https://www.badcaps.net/forum/showth...ighlight=x241w

[stevekasian]

Re: Acer X241W (Power Board Failure)

Ok, as a follow up, I have checked the 12v rectifier in circuit and found it to be conducting equally in all directions from P-N/N-P. I'm gonna remove it from the circuit tomorrow and check it again, but I believe that's a bad sign, especially considering it's the 12v pin on the rail that is registering no voltage.

I believe I should also order the caps circled in PlainBills annotated image in the other thread, as they are apparently the only ones that look to be original equipment on this board. I will give an update here tomorrow... Time for sleeeeeep.

SK

[dondrusco]

Re: Acer X241W (Power Board Failure)

Try to start with this post in another thread - AL2423W has the same power board
https://www.badcaps.net/forum/showpo...9&postcount=23

[stevekasian]

Re: Acer X241W (Power Board Failure)

The 12v rectifier checks ok out of circuit.

I did notice that 2 of the largest caps in the images above (19v section) were most likely replaced by a previous tech and are slightly too tall. As a result, the head skink "cap" that goes across all 3 sections put a lot of pressure on them when screwed into place, and it appears that one may have crumpled a bit under the stress. So I've ordered replacements for all the remaining OEM caps, as referenced in a previous post, plus all 3 of the largest caps (680uf@25V) in a shorter/smaller can.

So it looks like the middle of next week I should know whether or not this did the trick!
SK

[stevekasian]

Re: Acer X241W (Power Board Failure)

Ok, I changed out all the caps listed previously and still no dice. Anybody?

Thanks,
SK

[alexanna]

Re: Acer X241W (Power Board Failure)

What voltages do you see on CNS1?And is FS3 a fuse and dose it test good?

[stevekasian]

Re: Acer X241W (Power Board Failure)

CNS1 is not an issue, as the only problem is the backlight not coming on.

The voltages on CNS2, however, are. Please see photo #3 (annotated) for voltage readings there.

All fuses are good.

Thanks,
SK

[jetadm123]

Re: Acer X241W (Power Board Failure)

Have you tried checking the fuses on the inverter board?

[stevekasian]

Re: Acer X241W (Power Board Failure)

Yes. All fuses are good. All transformers read the same (chances are slim all 12 went out simultaneously).

As for voltages on the 19v rail being a problem, I could be mistaken but I don't understand what 5v would be doing on this rail. ?

[PlainBill]

Re: Acer X241W (Power Board Failure)

Yes. All fuses are good. All transformers read the same (chances are slim all 12 went out simultaneously).

As for voltages on the 19v rail being a problem, I could be mistaken but I don't understand what 5v would be doing on this rail. ?

Because, Doofus, that is the connector to the inverter. It carries ground, the 19V inverter supply and the inverter control lines - On/Off and Brightness.

Those voltages may indicate a problem with the signal card, or with the inverter.

PlainBill

[stevekasian]

Re: Acer X241W (Power Board Failure)

I know it's the connector to the inverter! :-p But everyone always says that the inverter only gets 12V or more. So the control lines are on the 5v lead?

And what is the "signal card"?
SK

[PlainBill]

Re: Acer X241W (Power Board Failure)

I know it's the connector to the inverter! :-p But everyone always says that the inverter only gets 12V or more. So the control lines are on the 5v lead?

And what is the "signal card"?
SK

1. The inverter POWER is often 12V, 18V, or 24V. The CONTROL signals are usually much lower 0-3.3V for Off/On and 1-3V for brightness.

2. The control lines come from the signal card. Don't confuse the power carried on a connector with the control signals on a connector. At least one manufacturer (Samsung?) feeds 15 volts to the signal card on one model.

3. The signal card is also called the video card, control card, or logic card. I prefer 'signal card' because most people will not confuse it with the video card in the computer, the power supply, or the panel card.

PlainBill

[stevekasian]

Re: Acer X241W (Power Board Failure)

Thanks for the info.

So how would you proceed with this at this point if this was your project?

[PlainBill]

Re: Acer X241W (Power Board Failure)

Thanks for the info.

So how would you proceed with this at this point if this was your project?

I'd put it on the shelf until I had the urge to work on it. Then I'd play 'Angry Birds' or help someone on the Badcaps forum until the urge went away.

OK, I'll try to offer some real help. First, the service manual is at Elektrotanya. That may help.

1. The manufacturer REALLY isn't helping; the pins on the power supply aren't labeled, which is unusual. I haven't seen pictures of the signal card, but they usually don't label the connector pins. The best hope is the inverter. That MIGHT give a clue.

2. As I mentioned, the two signal (control) lines are at unusual voltages. There are a number of reasons for this. Were the readings taken while the monitor was connected to a working computer? If not, that would explain the strange readings.

3. The fact that the backlights never come on, but the monitor does display a desktop leads me to suspect the inverter, in particular the fuses.

4. A simple test is to monitor the voltages on the two control pins in question while pressing the power button slowly. If the voltages change on every other button press, the problem MUST be in the inverter or possibly the backlights.

5. I took a look at the service manual, and surprisingly they had a schematic of the inverter. Pin 1 is On/Off, 2 is brightness, and there is a single fuse.

PlainBill

[alexanna]

Re: Acer X241W (Power Board Failure)

This may have been answered already but are we sure the controll lines for the back light are not on CNS1.I can make out 12V-ground-5V-Ground -On Off -Something? And what looks like ADJ.

[PlainBill]

Re: Acer X241W (Power Board Failure)

This may have been answered already but are we sure the controll lines for the back light are not on CNS1.I can make out 12V-ground-5V-Ground -On Off -Something? And what looks like ADJ.

They are. If you look at the picture of the back of the power supply two lines run from CNS1 to CNS2. This is a typical arrangement - the two signals originate on the signal card, pass through the power supply and go to the inverter.

The schematics in the Service Manual are pretty cheezy, but the one of the inverter is clear enough. OK, pin 1 is On/Off, and should be at 5V to turn the inverter on. Pin 2 is the brightness.

PlainBill

[stevekasian]

Re: Acer X241W (Power Board Failure)

> 2. I did not take the readings while a video source was connected. However, i did take the readings as i turned the monitor on and waited for it to go into standby mode. I got the 5V reading every time the display was supposed to be active (not in standby). So I guess that would be equivalent to "every other button press".

> 3. I checked the 2 fuses (yes, there are actually 2) on the inverter and they are not burned.

There is a single fuse on the PS board right at CN2 - perhaps that is what you are seeing on the schematic?

I found the service manual the other day, but unfortunately they really dropped the ball on the Power Board section... lol

[PlainBill]

Re: Acer X241W (Power Board Failure)

> 2. I did not take the readings while a video source was connected. However, i did take the readings as i turned the monitor on and waited for it to go into standby mode. I got the 5V reading every time the display was supposed to be active (not in standby). So I guess that would be equivalent to "every other button press".

Excellent - I was thinking that the readings were taken with the monitor in a standby state. That turns out not to be the case.

> 3. I checked the 2 fuses (yes, there are actually 2) on the inverter and they are not burned.

There is a single fuse on the PS board right at CN2 - perhaps that is what you are seeing on the schematic?

No, the first page of the inverter schematic clearly showed a single fuse at the power input. However, when examining the second page of the inverter schematic, they show a second fuse. And when I reexamined the first page, I find a third fuse. Just to be cute, they seem to be numbered F1, F2, and F101. I would expect F1 to be a smaller (physical and current rating) fuse than F101 and F2.

IF you locate all three fuses and they are intact, there are a few additional points to measure on the inverter. Transistors Q2, Q1, and Q3 handle level shifting of the On / Off signal. I suggest setting your DMM on the 20 volt range and measuring the voltage on the three pins of those transistors as you press the power button on and off. I would expect voltage changes on all pins of Q1 and Q3, and 2 of the three pins of Q2.

I found the service manual the other day, but unfortunately they really dropped the ball on the Power Board section... lol

That is a polite way of describing the utter lack of a schematic for the power supply.

PlainBill

[stevekasian]

Re: Acer X241W (Power Board Failure)

No, the first page of the inverter schematic clearly showed a single fuse at the power input. However, when examining the second page of the inverter schematic, they show a second fuse. And when I reexamined the first page, I find a third fuse. Just to be cute, they seem to be numbered F1, F2, and F101. I would expect F1 to be a smaller (physical and current rating) fuse than F101 and F2.

Well, it would've helped matters if I'd posted picts of the inverter board to begin with ;-) (see attached)

F1 is not in use on this board revision. (I swear I didn't cut it off - really)

(And apparently the explanation for the cute numbering job is that everything in the area of F101 is in the 100s.)

IF you locate all three fuses and they are intact, there are a few additional points to measure on the inverter. Transistors Q2, Q1, and Q3 handle level shifting of the On / Off signal. I suggest setting your DMM on the 20 volt range and measuring the voltage on the three pins of those transistors as you press the power button on and off. I would expect voltage changes on all pins of Q1 and Q3, and 2 of the three pins of Q2.

Thanks! I'll report back with results...

[PlainBill]

Re: Acer X241W (Power Board Failure)

Well, it would've helped matters if I'd posted picts of the inverter board to begin with ;-) (see attached)

F1 is not in use on this board revision. (I swear I didn't cut it off - really)

(And apparently the explanation for the cute numbering job is that everything in the area of F101 is in the 100s.)



Thanks! I'll report back with results...

There IS a reason I ask for pictures.

It appears someone has been working on the inverter with a pair of cutters. In addition to F1, I see three missing electrolytics. If you look at the assembly instructions in the service manual the three fuses and the caps are visible.

PlainBill