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Old 12-31-2010, 07:27 AM   #1
reneg
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Default Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Hello all!

This is my first post here, so please allow me to briefly introduce myself. My name is René and I live on the Faroe Islands and work as a computer programmer. I'm 26 summers old and I like to fix things myself. That's of course also why I happened to find this forum. :-)

I found this wonderful forum as I was searching the web for information on a specific inverter board, namely a TDK XAD306LR. I got this thread as a result: http://www.badcaps.net/forum/showthread.php?t=12454
I have been studying it, but unfortunately (Or luckily?) it's not the same problem I have. But I'm getting a bit ahead of myself here. First, what monitor are we talking about?

It's a 24.1" Sun monitor. It seems the product number is 365-1434-01. (It's called SunPN) The panel is a samsung LTM240M2 L02 which I found a specification sheet on from Samsung themselves. (I have attached this document)

The symptoms I'm experiencing is that the screen is totally dead. When I flip the switch on the power supply board, nothing happens. The screen power LED doesn't turn on or even blink, and neither does the CCFL lamps it seems. There is no flash or anything on the screen when it's turned on. There is of course a power button on the front of the screen itself, and I've tried pressing it, but nothing happens. The power button on the front of the monitor has a small LED to indicate what state the screen is in: Green = on, orange = standby. But the LED doesn't turn on at all.

I thought it was the power supply board (Which by the way is a FSP100-3P01, see attached photo) so I ordered a new one and replaced it. Unfortunately the screen reacted the exact same way as before. Nothing happens when I flip the switch on the back side of the monitor, and the power button on the front of the screen doesn't do anything either. And the power LED still doesn't turn neither green nor orange.

That was a bit disappointing, but I still hope I can fix it. The next thing I'm planning on doing is testing each CCFL lamp individually with a lamp tester (One of my friends works at a small consumer electronics store where they have a small repair shop. And he offered me to borrow a lamp tester).

But if any of you have any suggestions on other things I can test, I would really like to hear from you.

Also, do you think it sounds plausible that if a lamp was broken, the power LED doesn't turn on at all?

Any suggestions are really appreciated! Thank you!

Best regards
René
Attached Images
File Type: jpg Skærm 002_s.JPG (171.0 KB, 150 views)
File Type: jpg Skærm 003_s.JPG (203.9 KB, 87 views)
File Type: jpg Skærm 005_s.JPG (53.0 KB, 62 views)
File Type: jpg Skærm 006_s.JPG (60.6 KB, 68 views)
File Type: jpg Skærm 007_s.JPG (60.4 KB, 65 views)
File Type: jpg Skærm 011_s.JPG (143.8 KB, 64 views)
File Type: jpg Skærm 013_s.JPG (238.9 KB, 76 views)
File Type: jpg Skærm 014_s.JPG (192.8 KB, 43 views)
File Type: jpg Skærm 016_s.JPG (270.0 KB, 55 views)
File Type: jpg Skærm 017_s.JPG (255.9 KB, 68 views)
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File Type: pdf LTM240M2-L02.pdf (585.3 KB, 91 views)
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Old 12-31-2010, 09:38 AM   #2
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

I'm sorry, it seems I have placed my thread the wrong place. I believe it should be placed under "Troubleshoting Computer Displays". Is there a nice moderator who will move my thread? Thanks. :-)
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Old 12-31-2010, 09:38 AM   #3
retiredcaps
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by reneg View Post
Also, do you think it sounds plausible that if a lamp was broken, the power LED doesn't turn on at all?
Welcome.

First, great pictures and a description of the problem.

If the power LED does not come on at all, it usually means that there is no power going to the logic board (one with all VGA connector).

To verify this, you will need a multimeter to the DC voltages. On the left hand side of your power board there is a connector clearly marked with the voltages 5.3V, GND, and 5V sb. The 5V sb is your standby voltage. It should always be on and read 5V DC.

If you haven't used a multimeter before, please say so and we can guide you. Otherwise, check the voltages on that connector and report back.

edit: the mods are at http://www.badcaps.net/forum/showgroups.php. Send them a PM and anyone can move it.

Last edited by retiredcaps; 12-31-2010 at 09:40 AM..
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Old 12-31-2010, 10:39 AM   #4
jetadm123
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Since it looks like power passes through the middle board (usb board), I would also suggest that you look at this board for a blown fuse. A blown fuse might be telling the power board not to power on.
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Old 12-31-2010, 12:35 PM   #5
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Sounds like something with the logic board. If the logic board is dead, it will not turn on the power supply board. Check for any bloated/leaking caps and also check any fuses you find for continuity (they are typically labeled with F1, F2, F3... or something similar).

And as mentioned above, be sure to inspect the USB board as well.

The power board should also be putting out +5V standby power, which should be reaching the logic board. If there is no voltage reaching the board, you will know there is open circuit somewhere between it and the power board.
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Old 01-01-2011, 07:55 AM   #6
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Thank you so much for your replies!

I'm sorry my photo gave the impression that the power is going through the USB board. This is not the case, as can be seen on my attached photo. The wires are just bent so it looked like it. :-) The power is going straight to the logic board, and on the logic board is a small connector that is connected to the USB board.

I have used a multimeter a few times, but not really in regards to electronics and PCBs. So any hints, tips and warnings are much appreciated!

However, I measured the DC voltage on the connector as suggested and found 5V. However, due to the small schematic right next to the connector, I would have expected to find the voltage between a pin on the top and a pin on the bottom. But I didn't. There was no voltage between any of the pins this way. So I'm not sure then how to read the schematic, ie. which pin is which. But I tried measuring a pin and it's neighbor instead, and here I found 5V 2 places, as I've indicated on the attached photo. I measured this when almost everything was connected. The only thing not connected was the connector to the buttons on the front of the monitor. I can't access the boards when this is connected, otherwise I'll stress this cable too much and it shouldn't make a difference, should it?

Regarding fuses, I have tested the large fuse on the power supply board, right next to the switch and inlet. This fuse had a resistance of 0 or close to 0 ohm, so that should be fine. And I also tested the 3 small greenish fuses I could find on the inverter board, and they also had 0 ohm in resistance.
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File Type: jpg 012B_s.jpg (68.9 KB, 46 views)
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Old 01-01-2011, 08:35 AM   #7
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

I've been doing a little reading in some other threads and learned that I used an incorrect way of measuring the voltage. I read I should connect minus (-) to the frame or ground, and then put the plus probe on the pins on the connector. Also, it was mentioned that absolutely everything should be connected in order to be able to trust the readings 100%. So I connected everything and redid my measurements, and here are my readings.

5V standby: Both pins have 5V from the frame to the pin.
5.3V: Both pins have 0 - 0.05V. (Probably inside the error margin for my cheap multimeter)

I measured these voltages on the logic board, on the soldering joints where the connector is soldered on.
Also, I added a photo of my workbench so you could see how I connected the multimeter.
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File Type: jpg 010 (2)_s.JPG (138.8 KB, 62 views)

Last edited by reneg; 01-01-2011 at 08:43 AM.. Reason: Added photo of workbench + clarification
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Old 01-01-2011, 08:49 AM   #8
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

At the 5V and 5.3V connector you tested, on the right, there looks to be 2 fuses, FS2 and FS3. Test those and any other fuses on the power board (other than the one you already checked).
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Old 01-01-2011, 09:43 AM   #9
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

I've just tested those two, and they have between 0.03 - 0.05 ohm.
I looked around but couldn't find any other fuses on the board.
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Old 01-01-2011, 10:03 AM   #10
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by reneg View Post
I read I should connect minus (-) to the frame or ground, and then put the plus probe on the pins on the connector.
I usually use a ground screw closest to my test point for GND.

PS. I noticed that you have a red test lead with clip probe. That is, but I prefer to use a black so I know it is GND or COM. You may in the future get the 2 red leads confused and get a nasty surprise?
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Old 01-01-2011, 10:05 AM   #11
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

U7 on the logic board (top left hand corner in your pic) looks like a voltage regulator.

To test a voltage regulator, put your black probe on a ground screw and your red probe on pin 1. Then move the red to pin 2 and finally pin 3.

For a part number like AS1117-33, the 33 indicates an output voltage of 3.3V DC. An AS1117-18 would output 1.8V DC.

So list, measure, and report the results here.
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Old 01-01-2011, 11:29 AM   #12
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by reneg View Post
I've been doing a little reading in some other threads and learned that I used an incorrect way of measuring the voltage. I read I should connect minus (-) to the frame or ground, and then put the plus probe on the pins on the connector. Also, it was mentioned that absolutely everything should be connected in order to be able to trust the readings 100%. So I connected everything and redid my measurements, and here are my readings.

5V standby: Both pins have 5V from the frame to the pin.
5.3V: Both pins have 0 - 0.05V. (Probably inside the error margin for my cheap multimeter)

I measured these voltages on the logic board, on the soldering joints where the connector is soldered on.
Also, I added a photo of my workbench so you could see how I connected the multimeter.
This is a dual power supply. There are two sections; a standby 5V supply, and a main supply with 5.3 and 12? 24? volts for the inverter.

Those numbers indicate you have 5V standby, but the main power supply is not working. One of the lines from the logic board controls the main part of the power supply. That line should change state when you hit the power button on the monitor.

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Old 01-01-2011, 01:28 PM   #13
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by retiredcaps View Post
U7 on the logic board (top left hand corner in your pic) looks like a voltage regulator.

To test a voltage regulator, put your black probe on a ground screw and your red probe on pin 1. Then move the red to pin 2 and finally pin 3.

For a part number like AS1117-33, the 33 indicates an output voltage of 3.3V DC. An AS1117-18 would output 1.8V DC.

So list, measure, and report the results here.
I took a closer look at the component and the part number says "1084 0706AL". It's really hard to measure when the PCB is screwed onto the frame with the power supply, as the component is almost inaccessible and there is no soldering point on the opposite side of the PCB. How would you advise me to proceed; should I unmount the PCB and manuelly connect the 4 screwholes in the PCB with the frame using a wire? Or can I measure this without the PCB being grounded, as long as just my black probe is grounded?
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Old 01-01-2011, 02:16 PM   #14
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

You measure without the PCB grounded and wire your black probe to one of the ground screw holes on the PCB, not to the case since you just lifted the board out of it.
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Old 01-01-2011, 02:26 PM   #15
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

What is the part number of the chip circled in red? And the connector circled in yellow, is that connected to the pushbutton board?
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Old 01-01-2011, 02:58 PM   #16
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by Th3_uN1Qu3 View Post
You measure without the PCB grounded and wire your black probe to one of the ground screw holes on the PCB, not to the case since you just lifted the board out of it.
Great, thanks for the tip! I measured the 3 pins (Even though the middle one is not connected to anything) and got the following results:

Pin 1: 4.99V
Pin 2: 3.30V
Pin 3: 2.05V

(I've numbered the pins in the attached image)

Jetadm123 > The part number is "Z1010AI ZD7P14". Yes, you're right, the connector circled yellow is for the buttons on the front, and to the USB board. (There's 2 wires going from the USB board power connector to this connector)
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Old 01-01-2011, 03:45 PM   #17
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

On the Z1010AI can you tell if pin 2 is connected to the 5V or the 5.3V standby from the 8-pin connector to the power board? If you can't, just measure the voltage at pin 2.
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Old 01-01-2011, 04:29 PM   #18
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by jetadm123 View Post
On the Z1010AI can you tell if pin 2 is connected to the 5V or the 5.3V standby from the 8-pin connector to the power board? If you can't, just measure the voltage at pin 2.
When you say pin 2, where do you start counting? I don't think I can trace the pin on the board, as it seems some of the 'lanes' are inside the PCB. But I will measure it.

Thank you so much for your help and patience, jetadm123!
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Old 01-01-2011, 04:37 PM   #19
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by reneg View Post
When you say pin 2, where do you start counting? I don't think I can trace the pin on the board, as it seems some of the 'lanes' are inside the PCB. But I will measure it.

Thank you so much for your help and patience, jetadm123!


You follow a "U" pattern where pin 1 is at the small indentation (upper left) to pin 8 at the upper right.
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Old 01-01-2011, 04:56 PM   #20
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Okay, pin 2 has 5V.
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