Samsung 2253bw

[tscott33]

Hi, first time post. First of all, this is an awesome forum. I've used the information here to repair several LCD monitors. However, I'm stumped on this latest one (2253bw). It has the familiar problem of coming on for a second and then going dim. I've already recapped it but there's no change in behavior. What should I check next? Transistors? Xfmrs? CCFL? I searched the forum but couldn't find a service manual or schematic. It has the SEM2006 inverter. The blue power light stays lit steady.

The picture looks good for the second or so that it's on.

Thanks,
Scott

[PlainBill]

Re: Samsung 2253bw

Hi, first time post. First of all, this is an awesome forum. I've used the information here to repair several LCD monitors. However, I'm stumped on this latest one (2253bw). It has the familiar problem of coming on for a second and then going dim. I've already recapped it but there's no change in behavior. What should I check next? Transistors? Xfmrs? CCFL? I searched the forum but couldn't find a service manual or schematic. It has the SEM2006 inverter. The blue power light stays lit steady.

The picture looks good for the second or so that it's on.

Thanks,
Scott

Yes. Classic two seconds to black; use the classic tests.

PlainBill

[tscott33]

Re: Samsung 2253bw

Sorry for my ignorance but I'm not sure what you mean by classic tests. My experience fixing LCD monitors is limited to recapping them.

I was able to measure voltages at the inverter with the backlights unplugged:
VCC: 17V
UVLO: 6.8V
EN: 1.8V
FAIL: 0V
OVP: 0V
Vref Out: 5V

[cadillacman]

Re: Samsung 2253bw

Power it up. Look at the picture.

do the whites have a pink tinto to them ( before the backlights die out)?

if so you might have bad ccfls.

[tscott33]

Re: Samsung 2253bw

Thanks for the reply. No pink tint that I can see. No vertical lines either.

On the component side of the power supply board there is some discoloration like something got hot. It was like that when I got it. I'll post a pic later.

[jetadm123]

Re: Samsung 2253bw

Please post some photos of the entire power board front and back per PlainBill's links above. Power boards from different suppliers are used on Samsung monitors and your voltage readings are nice, but with no photos, we're all going to spend (waste) time second guessing each other. With photos, members can direct you to test specific items.

[tscott33]

Re: Samsung 2253bw

Best pics I could get of it...

[jetadm123]

Re: Samsung 2253bw

Okay, it looks like you're using some Lelon caps that are not the low-esr caps that are usually recommended here. Don't know the brand of the other ones that are being used. This can cause possible problems.

Sounds like you're getting 5V because of the solid power light. And it sounds like the CCFL's are trying to light.

At this point you might have one of the following problems:

1) Bad CCFL lamp(s).

2) Bad/damaged CCFL wiring from power board to CCFL lamps.

3) Bad inverter transformer.

4) Failed part in the CCFL error sense circuit causing the supply to shut down.

Do you have a spare CCFL lamp or LCD panel that you can use? You have 4 CCFL lamps, with power off, connect them all except for one and substitue a known good lamp. Turn the power on and see what happens. If the one you substitute causes all lamps to light, then you've found the bad lamp. When you disconnect and reconnect the CCFL connectors, make sure you power the monitor OFF because of the HIGH VOLTAGES!

I can't make it out on you second photo, but with power off, you will have to measure the secondary resistance of each inverter secodary. The secondary is what feeds the CCFL lamps. The difference between the two inverters should be 3% or less.


On post #3, were you measuring the CCFL controller chip to get those voltages?

[retiredcaps]

Re: Samsung 2253bw

Everything jetadm123 talks about is explained in more detail starting with post 13 and continued in 14 at

https://www.badcaps.net/forum/showthread.php?t=10419

[tscott33]

Re: Samsung 2253bw

I substituted a good backlight in each of the 4 backlight connectors (with the remaining 3 backlights still connected) and it lit up for 2 secs in each position.

I removed the 2 transistors and ohmed them and they were both the same:
pin 1 to 2: open
pin 1 to 3: open
pin 2 to 3: 5.1 kOhms

From the enclosed pic it looks like one of the stm8309 ICs smoked. It's the 8 pin IC on the right.

[PlainBill]

Re: Samsung 2253bw

Your test has effectively eliminated the CCLFs as the cause.

What caps did you use as replacements? jetadm123 refers to them as Lelon, I suspect they are Xicon. In either case, they are the most likely suspect. Replace them with low ESR caps such as Panasonic FR, FM, or FC series.

PlainBill

[jetadm123]

Re: Samsung 2253bw

Looks like the STM8309 overheated. Should be replaced in pairs. Only place I see them is on eBay.

[Scenic]

Re: Samsung 2253bw

black ones -> EPCOS (a.k.a. Siemens)
green ones -> Lelon
one brown one next to the wire harness -> chemicon
startup cap (to the right of the yellow transformer) -> *?*
blue one at the bottom also looks like a lelon

[retiredcaps]

Re: Samsung 2253bw

I circled what I think are the secondary inverter transformer pins. Set your multimeter to 2000 ohms (if manual). Measure the resistance between the yellow dots. Report readings. Do the same for the red dots.

[tscott33]

Re: Samsung 2253bw

I got 900 ohms for both transformers.

Looks like I can get a pair of stm8309 ICs for $11.90 on eBay or the entire board for $24.50.

And yes, I blew it on the re-cap

[retiredcaps]

Re: Samsung 2253bw

I got 900 ohms for both transformers.

Those readings suggest the inverter transformer is likely okay.