Acer AT1921 almost dead

[lidner]

Hi! I need some help with a Acer AT1921 LCD TV.
When I plug it in the LED lights orange for 1 second the it turns green and nothing happends. I have opened it up and looked for bulged caps but didnt find any. The backlight doesnt start either. Need any tip I can get.

[retiredcaps]

Re: Acer AT1921 almost dead

I have opened it up and looked for bulged caps but didnt find any.

The standard procedure here is to include pictures of your boards.

1) Post clear focused pictures AFTER reading

https://www.badcaps.net/forum/showthread.php?t=1868

2) Please do not post pictures inline as they slow down the loading of pages.

3) For best picture quality and clarity take your boards to a window on a sunny day, turn flash off, and use macro mode. Take a top down view of all your boards (front and back). Make sure the photo is legible so that we can read the PCB printing clearly. A shutter speed of 1/125 or faster will produce nice clear focused pictures. Try to get a photo that is 2000x2000 resolution or as close as possible.

4) Here is an example of the pictures we want.

https://www.badcaps.net/forum/showpo...94&postcount=1

5) Do you have a multimeter and can take voltage measurements?

[lidner]

Re: Acer AT1921 almost dead

Sorry for not following the standard procedure.

I now have taken some photos of the boards. I hope you can see th PCB
printing (dont really know what it is).

Yes I do have a multimeter and can measure voltage.

[retiredcaps]

Re: Acer AT1921 almost dead

I now have taken some photos of the boards.

Yes I do have a multimeter and can measure voltage.

Excellent photos. PCB is printed circuit board. We want to be able to read the lettering so we can tell you what to check.

For example, right above the white connector on the power board is a fuse F51.

With power off and lcd unplugged, measure the resistance. A good fuse should measure less than 1.0ohms depending on your multimeter.

[lidner]

Re: Acer AT1921 almost dead

Ok. Now I have measure the 3 Fuses (F1, F51, F52) on the power board and they seems to be ok.
I appreciate you help!
Do you have any other tip to look at?

[PlainBill]

Re: Acer AT1921 almost dead

The first question is this a case of the main board not instructing the backlights to turn on, or is it a case of the backlights not working? One way to answer the question is to hook up a signal source (Video game, DVD player, etc) and step through the inputs and see if you can hear the sound from the source. If you can't it's time to investigate the main board.

PlainBill

[lidner]

Re: Acer AT1921 almost dead

I have tried to connect a computer as source and used a flashlight to look if there was any "picture" shown and the backlight was broken but it seems to not start. I have also tried to connect a sound-cable but there is no sound comming from the speakers either, while the sources were connected I pushed the "Input" button so it should gon throug all inputs.

So I think that the backlight and the mainboard doesnt start as it should.

[PlainBill]

Re: Acer AT1921 almost dead

I have tried to connect a computer as source and used a flashlight to look if there was any "picture" shown and the backlight was broken but it seems to not start. I have also tried to connect a sound-cable but there is no sound comming from the speakers either, while the sources were connected I pushed the "Input" button so it should gon throug all inputs.

So I think that the backlight and the mainboard doesnt start as it should.

You are correct except for one detail. The main board controls the backlight.

My languages are rather limited. This site seems to have the main board. Or if you prefer, I suggest you test the voltage regulators on the main board. I've circled them in the attached picture. I've lettered them from A - H. I consider regulator A to be in the 'normal' orientation, and have numbered the points I want tested. I suggest using the point I circled in black (upper left corner) as the reference (ground point) for your meter.

What I would like for each of these regulators is the letter, the part number, and the voltage of each pin. If you look at them you may see that the part number breaks down into two parts AL1117-33; AL1117-25 for example. The first part is the same, the part after the dash is different. The first is a 3.3 volt regulator, the second is a 2.5 volt regulator.

PlainBill

[lidner]

Re: Acer AT1921 almost dead

The partnumber is the same for all of the regulators and it is "1084 PE 488IA" or maybe it's "4881A" ?
And the voltages on the pins are as follow.
A
1 2,18
2 3,44
3 5,05

B
1 0,71
2 1,97
3 3,43

C
1 2,17
2 3,44
3 5,08

D
1 0,68
2 1,95
3 3,44

E
1 2,17
2 3,44
3 5,08

F
1 0,71
2 1,98
3 3,44

G
1 2,18
2 3,44
3 5,01

H
1 0,71
2 1,98
3 3,42

I(the regulator next to the white connector,U29)
1 1,37
2 2,64
3 5,01

I hope it gives you any Ideas. For me it says nothing?

[PlainBill]

Re: Acer AT1921 almost dead

The partnumber is the same for all of the regulators and it is "1084 PE 488IA" or maybe it's "4881A" ?
And the voltages on the pins are as follow.
A
1 2,18
2 3,44
3 5,05

B
1 0,71
2 1,97
3 3,43

C
1 2,17
2 3,44
3 5,08

D
1 0,68
2 1,95
3 3,44

E
1 2,17
2 3,44
3 5,08

F
1 0,71
2 1,98
3 3,44

G
1 2,18
2 3,44
3 5,01

H
1 0,71
2 1,98
3 3,42

I(the regulator next to the white connector,U29)
1 1,37
2 2,64
3 5,01

I hope it gives you any Ideas. For me it says nothing?

Ideas? No. But it does give me some information. I expected these to be LDO (Low Drop Out) regulators. The current flow through the ground pin of an LDO regulator is very low. It is possible to use two resistors to adjust the output voltage of the regulator.

Notice the voltages at pin 3 (input) fall into two groups - 5 volts and 3.4 volts. Also, the voltage at pin 2 (output) is always 1.25 volts above the voltage at pin 1 (adjust). It appears the designers did that, and it appears the regulators are working properly.

At this point all I can suggest is replacing the main board.

PlainBill