Sun 24.1 LCD / Samsung 244T

[roadstir]

Hello, This is my first time on here and am greatly relieved to have a "go to" forum with so many knowledgable and generous contributors.

Ok, I saved up to finally purchase a 24.1" Sun monitor x7203a LTM240M2 L03I've always left it on and let it go into sleep mode when not in use. Then I read an article advising to turn it off at night. (beginning of the end) So I turned it off before bed and Voila...it would not turn on in the morning! There's usually a reassuring blue light on in the lower right corner. No more light of any kind. So, I found several bloated caps and sent it off to a gent on ebay who replaced the caps (hugheric, if anyones used him) However, I was greatly disapointed to find the light was still out along with my excitement.

1. Is there a way to bypass the 6 wire plug that goes to the frontpanel switches to see if the actual buttons/switch might be bad?

2. There are 5 white wires with a dark blue one on one end. Which wires would I jump?

3. When the power switch (on back of panel) is on I get no voltage running across the white replaceable fuse.

Thank you for any help you care to give.

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

21 views and no help? I should have made my title more interesting. lol
Can anyone offer me some assistance with this problem? This is a beautiful monitor and I hate to see it go down without a fight.

[Mr Bill]

Re: Sun 24.1 LCD / Samsung 244T

Have you tested the fuse since your not getting any voltage on the fuse? Did the Ebay seller test the power supply after repairing it?

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

Thanks for the reply, Mr. Bill!

I tested the fuse with a continuity tester and it's good. I also get 119.8 at each end of the fuse when power on. (After reading your email I realized I tried to test the voltage by putting a lead on each end, NOT putting the black on a ground and red on one end. )Yes, the repair person reaffirmed he tested they board before it left the shop.

[jetadm123]

Re: Sun 24.1 LCD / Samsung 244T

Suggest you plug in the power supply (leave the other boards disconnected from it) and measure the DC voltage at each wire of the wiring harness (the connector with the black wires coming out of it). Report the voltages you see.

If you see no voltages at the wiring harness, then measure the DC voltage across the large cap (100uf 450V). It should be around 390V.

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

Jet,

I have no voltage to the large wiring harness. When I checked the three wire harness I got 2.3v where it's marked 6.2v. The three nodes read on/off, gnd, and 6.2. When I checked the large capacitor it reads 166.2v.

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

What's odd is if I touch the ground at the corner lug and then red lead to the 6.2 node I get nothing. But if I connect the red and black to the side-by-side nodes (gnd & 6.2v) I get 2.3v?

[jetadm123]

Re: Sun 24.1 LCD / Samsung 244T

I'm not sure what the person "checked" to verify that the board is working. It doesn't even look like the power supply is starting up. You should at least have a standby voltage of 5 Volts, usually indicated on the board by something like 5_STBY or 5_SB.

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

Where can I find that 5_standby or 5s_b? On the top or bottom side? Would you have a photo where I can see this? My vision isn't the greatest and I can't seem to find these check points. What was the large cap reading off 166 indicative of?

Thank you for the help!

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

Large cap reads 374 when I touch red and black leads to both wires. Sorry, but I'm a novice at this and must have misread it before.

[jetadm123]

Re: Sun 24.1 LCD / Samsung 244T

The voltage output for each wire should be stamped onto the board itself near the wiring harness. Also, look underneath the board to see if anything is stamped there. If you see nothing, then it just adds to the hardship of trying to troubleshoot an already complex board.

Since you had trouble measuring the voltage across the cap, then I suggest you try measuring the voltages at the wiring harness again. If the wiring harness is labeled then list the expected voltage versus what you measured.

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

Jet,

Ok, here it is-

24 shows 0
24 shows 0
24 shows 0
24 shows 0
gnd
gnd
gnd
gnd
6.4 shows 0
6.4 shows 0
13 shows 0
13 shows 0
gnd
gnd

And the 3 wire harness shows

6.2 shows 2.23
gnd
on/off

[jetadm123]

Re: Sun 24.1 LCD / Samsung 244T

On your first photo, to the left of the large 100uf 450v cap is a metal shield. Directly above that shield appears to be a fuse. It's green in color and shaped like the resistor above it. Unplug your monitor and let it sit for a minute or two to let the large cap discharge. Check the fuse for contiunuity.

[jetadm123]

Re: Sun 24.1 LCD / Samsung 244T

Also, read this link as it looks like the problem may be similar to yours:

https://www.badcaps.net/forum/showth...highlight=244t

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

Jet,

Ok, that's the all green vs the banded one next to it, right? My meter buzzed happily when I touched the red and black on the ends. The case you kindly send the link to does sound very similar, though I'm no accomplished techie to quickly duplicate everything.

Plain Bill said that it is a two part power board- primary and secondary and that the secondary is always on. How do I tell the two sections apart? What should I check next?

Thank you for you patience and help.

[budm]

Re: Sun 24.1 LCD / Samsung 244T

Since you are getting about 374vdc on the large cap, it means that the PS_ON is OK, same for the PFC Voltage booster circuits. Can I get good clear pictures of the bottom side of the board, and four 1/4 section of the board so I can clearly see the trace, I need to see how the 24V power supply is made. Do the same for the top side also.
If you look at the picture of the power supply board in post 1 you will see large thick black line drawn on the board, the area in the left of the line is the deadly Primary side (the negative leg of that large cap is the ground ref point for the Primary side), the area to the right of the black line is the secondary side (cold side), the ground ref point for this section is tied to the chassis ground.

[jetadm123]

Re: Sun 24.1 LCD / Samsung 244T

The main thing that caught my attention in that link I sent you was the fact that not all the caps were replaced. Looking at your board, I noticed that one of the caps had a black mark (from a marking pen) on top of it. Typically, this is something done at the factory and leads me to believe that not all the smaller caps were replaced. What brand is this cap? CapXon? Sounds like the repair person used Nichicon caps. Other than the large 100uf CapXon cap, are there other non-Nichicon caps? I'm thinking especially the smaller caps. Hopefully it's something as simple as the startup cap for the 24V section that needs replacing.

As mentioned above, the PFC section is functioning and it looks like the secondary section for generating the voltages at the wiring harness is not working. The 24V section of the supply is what the other voltages are derived from.

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

Bud,

Here are the pictures you requested. Let me know if you need any redone. And thanks for explaining the Hot & Cold side for me.

Jet, good eyes. Yes, it looks as though he replaced the cold side caps with Nichicon (5 of them), but nothing on the hot side.

When I asked the cap repair person if he checked the board after replacing the caps this was his reply: "We do just replace the caps and check those components to ensure they are installed and working properly. As for the power supply itself...that board is the power, and it does get power, so the board is working properly..."

Thanks,

David

[roadstir]

Re: Sun 24.1 LCD / Samsung 244T

Photos of both sides.

[budm]

Re: Sun 24.1 LCD / Samsung 244T

Check RM801 (see picture number 2, 10) to see if it is open.
Check those 3 caps, and need P/N of that IC (mounted on the heatsink) for driving the 12v/24v transformer, I have a feeing that the IC is bad.