LCD Monitor problem - already replaced caps

[jmadaleno]

Hello all...
I'm John and i'm from Portugal.
In this 1st post of mine i'll ask for someone's help regarding a problem with a Samsung SyncMaster 920nw.

The problem with it is that when i turn it on the image shows for around 3 seconds and then disappears.

I've read somewhere that it could be faulty capacitors on the power supply board, so i replaced all of them except for the 400v100uF one (they were not bulged in any way, nor leaking).

After replacing them the problem still persists.



Thanks for your help and hope i can help someone too soon
John Madaleno

 

[tpetar]

Monitor is complete off ? Check power led On/Off status ?

If power led is On, check with flashlight if there is picture on screen. If you can see OS icons and rest elements on dark black screen probably you have dead backlight.



Best regards,
Peter

 

[jmadaleno]

When i have the power plug on, the power led is on, it works fine, the only problem is that when i turn it on i only get image for about 3 secs then it turns off again.

It shows the OSD "Check Signal Cable" or something like that but only for those 3 secs, then it turns off again.

If i press the power button again it shows the image again for another 3 secs and so on.

Thanks

 

[tpetar]

When monitor is Off power led is on with any color on monitor ?

 

[betwixt]

Sounds like the lack of signal detection is kicking in and putting it into standby mode.

Firstly, check that video is reaching the input socket and your computer is producing a picture in a mode the monitor can display. For example, if the computer is producing 1920x1080 video, the monitor will shut down in the manner you describe anyway.

Next check is to see what is on the screen for those 3 seconds. Is it only the "check signal cable" message or is there some computer video as well?

Then, try the menu buttons and see if the menu stays on the screen or whether it also goes off after 3 seconds. This will establish whether you have a display fault or a video fault, it seems more likely to be a video fault than a power supply problem to me.

Brian.

 

[jmadaleno]

Sounds like the lack of signal detection is kicking in and putting it into standby mode.

Firstly, check that video is reaching the input socket and your computer is producing a picture in a mode the monitor can display. For example, if the computer is producing 1920x1080 video, the monitor will shut down in the manner you describe anyway.

Next check is to see what is on the screen for those 3 seconds. Is it only the "check signal cable" message or is there some computer video as well?

Then, try the menu buttons and see if the menu stays on the screen or whether it also goes off after 3 seconds. This will establish whether you have a display fault or a video fault, it seems more likely to be a video fault than a power supply problem to me.

Brian.

It happens both with the computer connected to it and without.
For what i've seen on some youtube videos the "check signal cable" OSD msg should stay on it for a lot more time than just 3 secs.
Tried using the buttons but apparently there's no time for the menu to appear before it turns off.

Thanks for your replies, i'm testing as i'm reading

 

[betwixt]

Next checks:

1. unplug the video cable from the monitor. With the power switched off, measure the resistance from the middle pin of D101, D102,D103 and D105 to the other two pins. By middle pin I mean the one alone on one side of the package.

2. measure the resistance across the pins of ZD101, ZD102, ZD103, ZD104 and ZD105. Any of these shorted out might cause the symptoms.

3. With the monitor powered up and connected to a computer (so it would normally be working) measure the voltage at the junction of Q101 and R126.

4. under the same conditions, measure the voltage across C124.

All of these parts are on the main board. Let me know what the readings are.

Brian.

 

[jmadaleno]

i don't have any of those numbers in the board... all are 500+ and i can't find any ZD anywhere... i'll post a pic of the back of the board here in a bit...
here is the photo of the back of the board:

 

[betwixt]

Wrong board!

That's the power supply, all the components I mentioned are on the main board.

Brian.

 

[jmadaleno]

thanks for the heads up betwixt, i'll check it first thing in the morning and put values here.