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Old 01-08-2011, 05:02 AM   #41
PlainBill
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by reneg View Post
* bump *

Is anyone able to get any meaning out of the measurements I've made? Does it tell you anything?
You have to take a two pronged approach at this point. Trace the line from the power button to the main chip on the logic board. Does the input pin toggle? Similarly, trace the BL_ON pin from the connector to the power supply back to the output pin of the main chip on the logic board. Does the output pin toggle? (This would be easier if a schematic were available). Unfortunately, the most likely problem is the main chip.

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Old 01-08-2011, 09:07 AM   #42
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Sorry for the delay, but I had pretty much run out of ideas. Glad PlainBill stepped in and provided some fresh ideas.
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Old 01-08-2011, 10:14 AM   #43
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

One more thing - better pictures of the top and bottom of the logic card would be helpful.

Also what is the part number of the square chip to the left of the large processor (U3?). That MIGHT actually be the standby controller.

OK, that's two things.

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Old 01-08-2011, 07:10 PM   #44
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Thank you for your replies!

PlainBill, do you mean the IC I've taken a macro shot of? It's a Realtek RTD2120L. I found the data sheet and have attached it. The main IC is a Realtek RTD2549T. I couldn't find any data sheet on it, but I managed to find one for a RTD2523. I thought it would be better than nothing as they do look similiar. The data sheet is available here: http://cnpdf.alldatasheet.com/datash...2/RTD2523.html

The two IC's to the right of the main IC is SDRAM. The part number is ESMT M12L64322A. I found the data sheet in case it's of any help and attached it.

About tracing the pins, I'll get on it but it'll probably take some time for me. Also I'm not really sure how to trace the power signal from the power button. When I look at the diagram I made, where does the signal from the power button go? Please excuse my ignorance here, but I don't understand where the signal goes out when all the pins are connected to eachother through resistors.
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File Type: jpg 006 (2)_s.JPG (143.5 KB, 30 views)
File Type: jpg 009 (2)_s.JPG (376.0 KB, 23 views)
File Type: jpg 010 (3)_s.JPG (362.1 KB, 20 views)
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File Type: pdf M12L64322 (1).pdf (821.1 KB, 43 views)

Last edited by reneg; 01-08-2011 at 07:17 PM..
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Old 01-09-2011, 06:16 AM   #45
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by reneg View Post
Thank you for your replies!

PlainBill, do you mean the IC I've taken a macro shot of? It's a Realtek RTD2120L. I found the data sheet and have attached it. The main IC is a Realtek RTD2549T. I couldn't find any data sheet on it, but I managed to find one for a RTD2523. I thought it would be better than nothing as they do look similiar. The data sheet is available here: http://cnpdf.alldatasheet.com/datash...2/RTD2523.html

The two IC's to the right of the main IC is SDRAM. The part number is ESMT M12L64322A. I found the data sheet in case it's of any help and attached it.

About tracing the pins, I'll get on it but it'll probably take some time for me. Also I'm not really sure how to trace the power signal from the power button. When I look at the diagram I made, where does the signal from the power button go? Please excuse my ignorance here, but I don't understand where the signal goes out when all the pins are connected to eachother through resistors.
Bingo!!! It seems very likely the RTD2120L is the standby controller. I'm not going to have the free time to assist you for a few days, but here is the approach I would take. Examine the datasheet and identify which package you have. Verify you have Vcc at the power pins of the IC. Verify the voltage on the reset input. Then see if you can identify which of the 44 pins on the IC changes level when you push the power button.

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Old 01-09-2011, 09:17 AM   #46
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

I measured the voltage on all of the pins on the IC (Whew! Glad I had a magnifying glass!) and wrote down my results. I wrote them on the diagram of the IC from the data sheet. The only pins that changed voltage when I pressed the power button was pin 10 and (maybe) pin 29. It seems pin 10 is the one receiving the input from the power button. When I'm not touching the power button, the voltage was 3.12V and when I pressed the power button, the voltage decreased to 0.55V.
Pin 29 had 3.13V when I was not touching the power button, but when I pressed the power button it decreased to 3.12V (Difference is 0.01V). However, I'm not 100% certain because of the error margin, but the voltage did seem to react when I pressed the power button.

But I'm a bit puzzled as the data sheet says that pin 29 and pin 32 is "NC" and should not be connected to anything other than ground. So there shouldn't be any voltage, should there?

Regarding the RESET pin (Pin 4) the measured voltage was 1.79V. I don't know if that's enough or if it should be 3.12V? And what is the RESET pin used for? (Well, for resetting obviously, but what does that mean in this context?)
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Old 01-09-2011, 02:06 PM   #47
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by reneg View Post
I measured the voltage on all of the pins on the IC (Whew! Glad I had a magnifying glass!) and wrote down my results. I wrote them on the diagram of the IC from the data sheet. The only pins that changed voltage when I pressed the power button was pin 10 and (maybe) pin 29. It seems pin 10 is the one receiving the input from the power button. When I'm not touching the power button, the voltage was 3.12V and when I pressed the power button, the voltage decreased to 0.55V.
Pin 29 had 3.13V when I was not touching the power button, but when I pressed the power button it decreased to 3.12V (Difference is 0.01V). However, I'm not 100% certain because of the error margin, but the voltage did seem to react when I pressed the power button.

But I'm a bit puzzled as the data sheet says that pin 29 and pin 32 is "NC" and should not be connected to anything other than ground. So there shouldn't be any voltage, should there?

Regarding the RESET pin (Pin 4) the measured voltage was 1.79V. I don't know if that's enough or if it should be 3.12V? And what is the RESET pin used for? (Well, for resetting obviously, but what does that mean in this context?)

Try tracing what's connected to the reset pin (pin 4). It may be fed by 3.3V through diodes, resistors, transistors, etc. Test these components for shorts.
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Old 01-09-2011, 03:12 PM   #48
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by jetadm123 View Post
Try tracing what's connected to the reset pin (pin 4). It may be fed by 3.3V through diodes, resistors, transistors, etc. Test these components for shorts.
A few comments:

1. Reset appears to be generated internally, still the voltage is strange. I'd expect either less than .4 volts or more than 2.5 volts.

2. Pins marked 'NC' are often connected internally.

3. This chip contains internal flash memory. If that is corrupted the chip will not work.

While additional testing can be done, I'm not optimistic about having any success.

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Old 01-10-2011, 01:30 AM   #49
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

reneg: It looks like you have been very thorough in your work. The front panel buttons and circuitry is probably good. Hard to say if the RTD2120 is working properly, but in my opinion this type of digital logic chip is unlikely to fail.

I'm guessing there is some major fault somewhere. To narrow this down I would try disconnecting the major circuit assemblies. For example, what happens if you disconnect the LCD panel from the video/logic board. Does it power on and light the backlight? What if you disconnect the backlight and leave the LCD panel connected? Can it display a very dim image on the LCD? Do the front panel LEDs stay on? What if you disconnect the backlight and LCD panel? (If you disconnect the backlights, unplug the low voltage input cable only.) Powering the monitor with these circuits disconnected should be safe. I've done it on monitors before. But it is an unusual thing to do.

Also. It might be worth mapping out the power supply circuitry. Like, which supply powers each circuit block? I think you found the voltage regulator U7 was working, with an output of 3.3 volts. The DC-DC converter U8 AOZ1010 should be investigated further. Also, I noticed some small transistors Q4 and Q5 on the video/logic board. These *might* be power supply switching transistors.

Once you understand all of the main power wiring you can start to test the main component blocks. Are they getting power? Do they get power at the right time? Do they get power when you press the power-on? Are they getting power intermittently? Of course if the manufacturer could send you a schematic........

An oscilloscope would be useful if you could get one.
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Old 01-11-2011, 05:39 PM   #50
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

PlainBill, Jetadm123 > Thank you both for sticking with me and still suggesting things I can try.

Ken256 > Thank you, that sounds like a good idea to try! I'll do that ASAP.

However, my wife and I are going on vacation for 14 days starting this thursday, so I have to pause this project. I will post back in this thread when I'm back and I've tried your suggestions.

Best regards
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Old 03-02-2017, 06:26 PM   #51
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

On the off chance that reneg gets notified when a post is made, I was hoping he could tell me how he opened the Sun Monitor. I have one myself with what I think is a burnt out bulb, but I haven't been able to nicely open the case. I've removed all visible screws. I'm guessing there are clips, but I don't know how to disengage them without bending the crap out of the frame.
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Old 12-17-2017, 08:25 AM   #52
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

I'm wrestling with one of these myself, wondering if I should open another thread...?

Anyway, to the last poster, Luke, opening up the case is one of the hardest I've come across, the clips hold it together quite tightly. Anyway, there are two easy screws on the bottom edge, and a clip exactly in the middle between the two screw positions. There are two more clips along the bottom edge, about the same distance either side of the screws, as the centre clip is from the screws. You need to be quite forceful as there are additional "stays" that help prevent the bezel bending out as you try to pop it out, but start with the middle one, and keep working out towards the corners slowly (left, right, left, right, etc.), and it should eventually yield. I broke a couple of plastic spudgers trying, and eventually had to use a stiff knife and flathead screwdriver to work it off. Hard not to damage, but once the bottom edge is released and then the first corner going up, it works off easier up along the sides. First clips up along the sides are almost in the corner, so be careful with those ones, then it should be plain sailing after that.

Regarding my problem with my monitor, mine is the exact same model as the OP. However, mine does come on. DVI is working, and I initally thought VGA wasn't working with a desktop PC, but plugging in a laptop to VGA out, and I get a picture.

The problem with mine is that 3 of the 5 buttons along the bottom edge of the monitor don't do anything. The buttons are, left to right, <, >, POWER, MENU and SOURCE. Only < and POWER seem to work, < brings up a brightness menu, and pressing it again will reduce the brightness, but > does nothing. POWER will turn the monitor on and off. And MENU and SOURCE don't do anything either.

I've tested the actual buttons, and they do work (continuity test at the button contacts, on and off), and they also work all the way back to the logic board (continuity all the way back from each of the buttons). So it looks like an issue at the logic board.

I roughly tested all the resistors on the logic board where the buttons are connect to, and didn't find any shorts. No visible damage anywhere on the board.

Where do I go from here?
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Old 01-04-2019, 05:05 PM   #53
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

To tmcw:

Greetings! I know this thread is a year old, but I was wondering if you had any luck with your Sun monitor?

The symptoms you are showing (only Power and <- button working) are exactly the same symptoms I have. In fact, I just acquired several of these and of the 3 I've tested so far, they ALL show this issue. So, I'm kind of desperate to see if it's fixable. I was thinking maybe it was a panel / button lock of some kind, but I've tried various key combinations to try and unlock it, but had no success.

Did you ever get yours working?

Thanks!
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Old 01-05-2019, 12:36 AM   #54
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

regarding tmcw and timbered's posts above: I've seen a very similar issue on a Dell monitor. Forgot what model it was. But the issue it had was that some buttons would stop working / stop responding when hot, while others would trigger the menu. From what I was able to track down (couldn't manage to fix it in time), the issue was bad implementation of the logic of the buttons, which over time, became sensitive to values drifting of components (particularly the main chip) and mis-interpreting the button signals.

Not sure if this would be the issue here. But very good close-up pictures of the logic board and button board might help.
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Old 01-05-2019, 03:45 AM   #55
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Thank for the suggestion. But my mystery is deepening.

Here's some further info.

I have a bunch of these. I took three, plugged them into my desktop DVI cable, and got the only-two-buttons-are-working-no-onscreen-menu issue.

So, I then took one of those over to my workbench, plugged it into the laptop there with an analog VGA cable, and Lo and Behold, all the buttons were working! I was able to reset it back to the factory settings, turned it off, and tried a second one. Same thing - buttons were now all working. Third one, again, all working on my laptop with analog VGA. Pulled a fourth out of the pile, one I hadn't tried on my desktop system, plugged it onto the laptop, same way as the other three. And oops! Only two buttons work! Just like the others on my desktop system. Wtf?

I take one of the three that I've already is verified working and had reset, plugged it back into my laptop. Ugh! It's back to only two buttons again, no OSD, no menus, nothing! I wiggle cables, reverse ends, turn my laptop off / on, try different resolution and clock settings, still can't get it back to having the menu buttons working.

So, something very strange is going on, and I'm now about 60/40 for it being a firmware issue and not a hardware issue. But I've spent another hour or so trying different combinations trying to recreate what I did to get them working, and haven't hit upon it.

I'm calling it a day for now, and will try again tomorrow.

Thanks again for your input, and I welcome any ideas of what I should try.

T.
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Old 01-05-2019, 08:36 PM   #56
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Greetings again!

I thought I would let the perhaps only two other people on the planet who actually may care about this issue know that I have solved it.

Apparently, if you tilt the monitor back more than about 45 degrees, it dims the screen and shuts off access to the on-screen menu - the symptoms that I had described where only the screen dimming button worked.

I suppose this is a safety "feature" to keep the heat from the 6 CFL lamps, PS, circuit boards, etc. from turning the thing into a frying pan and cooking the LCD panel. Which makes sense if you think about it.

However, it would have been nice if this was mentioned in the manual

That would have saved me hours of aggravation...

Anyway, thanks for the suggestions!

So, here's to fixing by accident!
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Old 01-09-2019, 01:50 AM   #57
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Have just seen the extra posts here, and the PMs from timbered, thanks for following up on this and posting a possible fix.

I still have the monitor, but didn't get any further with it. I was hoping at the least that I might be able to use it with a Dreamcast console, for playing the odd vertical shooter, but the picture size through VGA was only about 1/4 of the total size, so I shelved the monitor, not being able to access the menus to see if I could change resolution or frequency. So I did put the monitor into a vertical position, the buttons still didn't work, but I don't think I put the monitor back to a horizontal position to recheck if the buttons worked.

I'm away from the monitor for about 2-3 weeks, but will check it again then, and will post back my findings. I didn't notice a mercury switch you mentioned on your PM. I presume it protects the screen to only allow it to be used in a horizontal, fairly upright position, may be it can be adjusted so that it can be used in a vertical position, though if it works properly in horizontal, it might be more value running it as intended, as a PC monitor.

Anyway, thanks again for posting your fix.
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Old 01-09-2019, 12:36 PM   #58
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

Quote:
Originally Posted by timbered View Post
Apparently, if you tilt the monitor back more than about 45 degrees, it dims the screen and shuts off access to the on-screen menu - the symptoms that I had described where only the screen dimming button worked.
Interesting. But I find this rather strange, as I don't see a tilt switch on any of the boards in any of the pictures that people posted here. Perhaps there is one on the T-con board (a long board on top of the LCD monitor, typically under a separate metal shield). Otherwise, I don't see how the monitor would detect the tilting.

In any case, I also noticed that the pictures of the logic board uploaded here by reneg and others indicate that the board has CapXon capacitors. In which case, I recommend doing a recap of the logic board, even if this may not seem to have anything to do with the issue. I've seen too many CapXon caps go bad over the years that I just don't allow myself to leave them anymore - they almost always fail.
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Old 01-21-2019, 03:49 AM   #59
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

With the monitor off, I can actually hear something click when I tilt it back and forth.

I was actually joking about the mercury switch, since when I sent that, I hadn't discovered the clicking. It's towards the right side as you're facing the screen, about halfway between top and bottom. I'm assuming this is the tilt switch, and it's mounted somewhere within the steel frame and not on the boards.

I haven't gotten to one that isn't working yet, so I don't have one to tear apart. If / when I do, I'll let you know if I find it.

Thanks!

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Old 01-21-2019, 04:01 AM   #60
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Default Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)

I figured you were joking about the mercury switch, but it's possible there is a switch that detects the orientation of the panel.

I'll be back at mine later this week, Friday or Saturday, and mine still has the bezel off, so it will be easy to get back into it to have a look and take some photos.
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