Samsung Syncmaster 245BW

[stewart710]

Hi, I'm a longtime lurker around here and have fixed a few lcd's with the help of some of these threads, so thank you in advance. I can't find much info on common issues with this 24" LCD. I ran across a couple of websites with people mentioning my exact problem, but no solution. The monitor powers on, the blue power Led comes on, but there is no image displayed. I have tried shining a light at it, but cannot see any image. I tried this with a DVI cable and VGA cable hooked up to my computer, no dice. The only thing I did notice is that my computer can detect the monitor and knows what resolutions it supports. Also after the computer goes to standby the blue Led on the monitor starts blinking. It comes back on when I wake the computer. This suggests that the lcd motherboard is functioning properly.

So I popped open the case, kind of annoying design, no screws just those pop tabs around the edges. I couldn't find any evidence of bulging caps, even though they are CapXon on the inverter and SamWha on the power board. The motherboard (or whatever it's called) has only polymer caps, so nothing obvious there. I replaced the 4 Capxon 220uf 35v (with Elna RJH caps, I know someone is gonna ask) guys on the inverter, but it didn't help. I then moved onto the power board. Both glass fuses are working. I replaced a couple of SamWha 100uf 35v with 2 100uf 25v caps (KY series, forgot the manufacturer). The transformer handles up to 24v, so I figured this was ok temporarily. No change. I looked at the power board and noticed a little evidence of heat on one of the diodes (FCH20A10). I removed it and it tests out OK. There is a slight bit of voltage getting through but it is like .002v difference when I put the + on the cathode and the black on the outer legs of the diode. I am kind of stumped here. Anyone have any suggestions?

[PlainBill]

Originally Posted by stewart710

Hi, I'm a longtime lurker around here and have fixed a few lcd's with the help of some of these threads, so thank you in advance. I can't find much info on common issues with this 24" LCD. I ran across a couple of websites with people mentioning my exact problem, but no solution. The monitor powers on, the blue power Led comes on, but there is no image displayed. I have tried shining a light at it, but cannot see any image. I tried this with a DVI cable and VGA cable hooked up to my computer, no dice. The only thing I did notice is that my computer can detect the monitor and knows what resolutions it supports. Also after the computer goes to standby the blue Led on the monitor starts blinking. It comes back on when I wake the computer. This suggests that the lcd motherboard is functioning properly.

So I popped open the case, kind of annoying design, no screws just those pop tabs around the edges. I couldn't find any evidence of bulging caps, even though they are CapXon on the inverter and SamWha on the power board. The motherboard (or whatever it's called) has only polymer caps, so nothing obvious there. I replaced the 4 Capxon 220uf 35v (with Elna RJH caps, I know someone is gonna ask) guys on the inverter, but it didn't help. I then moved onto the power board. Both glass fuses are working. I replaced a couple of SamWha 100uf 35v with 2 100uf 25v caps (KY series, forgot the manufacturer). The transformer handles up to 24v, so I figured this was ok temporarily. No change. I looked at the power board and noticed a little evidence of heat on one of the diodes (FCH20A10). I removed it and it tests out OK. There is a slight bit of voltage getting through but it is like .002v difference when I put the + on the cathode and the black on the outer legs of the diode. I am kind of stumped here. Anyone have any suggestions?

Quite a few. The flashlight trick sometimes works, sometimes doesn't. It seems to depend on the characteristics of the panel. The symptoms you describe suggest a non-functioning inverter.

I'd like two more pictures, and you can make one test. I'd like better pictures of the bottom of the board, covering the area around the connector to the inverter, and another covering the connector to the logic card. There are labels there that I can't read.

Also, there is a fuse on the inverter. Have you checked that?

PlainBill

[stewart710]

Hi Bill, thanks for taking the time to look at this. I checked what I believe is the fuse on the inverter and it is OK. It is labeled 125v 6.3A and it is a white rectangular surface mount chip. Here are some pics of the logic board and the back of the power board that you asked for.

[PlainBill]

Originally Posted by stewart710

Hi Bill, thanks for taking the time to look at this. I checked what I believe is the fuse on the inverter and it is OK. It is labeled 125v 6.3A and it is a white rectangular surface mount chip. Here are some pics of the logic board and the back of the power board that you asked for.

OK, a couple of points. One is that I am pretty good at reading legends on PC boards. I also can read upside down. Combine the two - I'm not so good.

On the connector to the inverter there are sections labeled +24V, GND, SOS(?), BL, A_DIM, and ST/P DIM Check for the presence of +24 volts, and the BL pin should toggle when you hit the power button on the monitor. I don't have a clue what SOS means other than something inedible served in the high school cafeteria.

On the power connector to the logic card, please verify the voltages are present.

PlainBill

[stewart710]

I'm an idiot, sorry I didn't even notice I did that. Here are the power boards right side up. I checked the voltage going to the inverter board: the +24v are putting out .229v and the BL is toggling from .18v (off) to ~.2v then back down to ~0v when switched on. I just realized you asked for the logic board side, not the inverter, I'll have to try again tomorrow. The way this thing is put together is very strange. The only way I could test it with everything still plugged in was to use the terminals on the connector on the inverter coming form the cabling that goes to the power board. I'm heading to bed for the night, but I'll be back at it tomorrow evening. Thanks again.

[PlainBill]

Originally Posted by stewart710

I'm an idiot, sorry I didn't even notice I did that. Here are the power boards right side up. I checked the voltage going to the inverter board: the +24v are putting out .229v and the BL is toggling from .18v (off) to ~.2v then back down to ~0v when switched on. I just realized you asked for the logic board side, not the inverter, I'll have to try again tomorrow. The way this thing is put together is very strange. The only way I could test it with everything still plugged in was to use the terminals on the connector on the inverter coming form the cabling that goes to the power board. I'm heading to bed for the night, but I'll be back at it tomorrow evening. Thanks again.

Sounds like this may be a case of no +24 Volts out of the power supply.

PlainBill

[stewart710]

I guess I need to test the transformer and see if I can replace it.

[Radio Fox]

Originally Posted by stewart710

...I then moved onto the power board. Both glass fuses are working. I replaced a couple of SamWha 100uf 35v with 2 100uf 25v caps (KY series, forgot the manufacturer). The transformer handles up to 24v, so I figured this was ok temporarily...

I am wondering why you chose the 100uF caps to replace? The more likely candidates to go faulty would be the higher value caps, such as 1000uF.

[PlainBill]

Originally Posted by Radio Fox

I am wondering why you chose the 100uF caps to replace? The more likely candidates to go faulty would be the higher value caps, such as 1000uF.

Most SMPS controllers use one or two electrolytic caps in the 22 - 100 µF range. These provide filtering for start-up and run power. When these fail they do not provide any visual sign. As a matter of routine, it is prudent to replace them. It is elating to replace $9.00 in caps and bring back a monitor from the dead. It is much less delightful to open the monitor up two months later to replace $.50 in caps.

PlainBill

[PlainBill]

Originally Posted by stewart710

I guess I need to test the transformer and see if I can replace it.

Probably not the transformer. I haven't studied the power supply design. First you verify the +24 volt supply is dead, then we find the cause.

PlainBill

[stewart710]

Originally Posted by Radio Fox

I am wondering why you chose the 100uF caps to replace? The more likely candidates to go faulty would be the higher value caps, such as 1000uF.

You're right, it was a typo. They were 1000uF caps which was part of the reason I chose, also because I had replacements handy.

[Radio Fox]

Originally Posted by PlainBill

Most SMPS controllers use one or two electrolytic caps in the 22 - 100 µF range. These provide filtering for start-up and run power. When these fail they do not provide any visual sign. As a matter of routine, it is prudent to replace them. It is elating to replace $9.00 in caps and bring back a monitor from the dead. It is much less delightful to open the monitor up two months later to replace $.50 in caps.

PlainBill

Yep. I agree entirely.

Only a couple of weeks ago I replaced 9 capacitors in a faulty Hyundai N91W. 5 of them were bulging, but I thought I would replace the other 4 large ones in the general area of the others (all Samxon). I replaced them with Panasonic FM's. There was only 1 other electrolytic on the board that I left. It was a small Samxon 47uF 25v.

After just 2 weeks the monitor failed again! Yep, it was the 47uF. The only elctrolytic that I didn't change! It was reading 6 Ohms on the ESR meter. Changed it yesterday for a Panasonic. Working again...so far.

Anyway, I was wondering why stewart710 changed those 2 only, when there are 14 electrolytics on the board, but as he has now said, it was a typo, & it was the 1000uF caps that were changed.

[stewart710]

Originally Posted by Radio Fox

Yep. I agree entirely.

Only a couple of weeks ago I replaced 9 capacitors in a faulty Hyundai N91W. 5 of them were bulging, but I thought I would replace the other 4 large ones in the general area of the others (all Samxon). I replaced them with Panasonic FM's. There was only 1 other electrolytic on the board that I left. It was a small Samxon 47uF 25v.

After just 2 weeks the monitor failed again! Yep, it was the 47uF. The only elctrolytic that I didn't change! It was reading 6 Ohms on the ESR meter. Changed it yesterday for a Panasonic. Working again...so far.

Anyway, I was wondering why stewart710 changed those 2 only, when there are 14 electrolytics on the board, but as he has now said, it was a typo, & it was the 1000uF caps that were changed.

Thanks for catching my mistake. In the stuff I have fixed successfully, it seems there are normally multiple caps with problems and at least one of them has visible signs. So I normally replace all the caps of a given size/brand that show any signs of failing or ones that are known to cause problems. If it works, then I would go back and order the correct parts to replace them all. If I had the correct sizes of caps for the rest of the board on hand, I would replace them as well. I just wanted to make sure that I wasn't barking up the wrong tree before I ordered anything. If the best course of action to replace every cap on the power board now before proceeding, I would. I just wanted to get some help before I go blindly ordering parts that may not fix the problem.

[stewart710]

Bill,
So the 24V is only connected to the inverter side, not the logic board, which reads ~0.225v. the Logic board gets a connection labeled PSON which reads ~3.2v and 5.2v Standby which reads 5.2v. It also has 3x connections that are supposed to supply 5.3v, but they all read -0.001v.

[PlainBill]

Originally Posted by stewart710

Bill,
So the 24V is only connected to the inverter side, not the logic board, which reads ~0.225v. the Logic board gets a connection labeled PSON which reads ~3.2v and 5.2v Standby which reads 5.2v. It also has 3x connections that are supposed to supply 5.3v, but they all read -0.001v.

OK, this is getting complicated. Looking at the power supply board, it is obvious there are two SMPS transformers, plus what appears to be a PFC stage. Unfortunately, I can't read the labels. I've marked up what I can identify.

PlainBill

[stewart710]

Bill, here is another picture of the whole board, there are also closeups in post #5 of the sections of the board that are marked as hard to read. I checked the fuse you pointed out and there is a connection across it. Does this mean there are two separate problems: one with the 5.3v supply and one with the 24v supply?

[PlainBill]

Originally Posted by stewart710

Bill, here is another picture of the whole board, there are also closeups in post #5 of the sections of the board that are marked as hard to read. I checked the fuse you pointed out and there is a connection across it. Does this mean there are two separate problems: one with the 5.3v supply and one with the 24v supply?

This one had me puzzled; it turns out it was a misconception on my part. I had you confused with someone who had an image visible on the screen when a flashlight was used. I reread the first post and the problem it is much clearer.

As I stated in the earlier post, this power supply appears to contain a PFC 'front end', and two power supplies, the standby supply, and the main supply.
The main supply has 5.3 and 24 volt outputs, derived from a single transformer.

The symptoms you describe would indicate the main supply is either not instructed to turn on, or fails to turn on. The behavior of the power LED leads me to believe it is the latter problem. Unfortunately, I can't identify the control line on the photos!!

PlainBill

[PlainBill]

I've decided to take a different approach. I've marked what appears to be the power supply controller. What is the part number? I've also circled a couple of caps that are prime suspects.

PlainBill

[stewart710]

The part has an FE P on the top line (probably the manufacturer). Then F9222L, then 6N330 on the lower line. The caps look OK even though my picture suggests leaking. The tops are flat and shiny, not sure where the reddish-brown reflection came from in the photo. They are 47uf 50v and 10uf 50v. SamWha RD series rated for 105C. I have a low-esr replacement for the 10uf, but all I have for the 47uf is a 100v 47uf SMG series rated for 85C, I don't know what brand, assuming it's not low ESR. Should I use it?

[PlainBill]

Originally Posted by stewart710

The part has an FE P on the top line (probably the manufacturer). Then F9222L, then 6N330 on the lower line. The caps look OK even though my picture suggests leaking. The tops are flat and shiny, not sure where the reddish-brown reflection came from in the photo. They are 47uf 50v and 10uf 50v. SamWha RD series rated for 105C. I have a low-esr replacement for the 10uf, but all I have for the 47uf is a 100v 47uf SMG series rated for 85C, I don't know what brand, assuming it's not low ESR. Should I use it?

The first step would be to locate the data sheet and verify power is reaching the IC, and the control signal is in it's proper state. A quick search for a data sheet didn't turn it up.

The caps are a second possibility. Given you have replacement caps, I'd give them a try. I don't believe the ESR rating is critical on these parts.

PlainBill