Samsung Syncmaster 245BW

[pegasus5334]

Re: Samsung Syncmaster 245BW

THANK YOU ALL

[dbinokc]

Re: Samsung Syncmaster 245BW

I have a 245BW that shows no display, but the blue power switch lights up.
I have already pulled the monitor apart and started checking some voltages.
There is no 24V out. No obvious bulging caps or blown components.

At first I thought I had found a clue when I connected my multimeter to look at VCC of ICB801S. I saw about 15V AC. To get a closer look I connected my scope and I am seeing see -150VAC rectified which makes absolutely no sense. Every component in this part of the circuit should be blown to bits! Not sure why I was seeing 15V AC except maybe because it was not a pure sine wave was throwing off my cheapie meter.
Are the power supplies running a floating ground?

[PlainBill]

Re: Samsung Syncmaster 245BW

I have a 245BW that shows no display, but the blue power switch lights up.
I have already pulled the monitor apart and started checking some voltages.
There is no 24V out. No obvious bulging caps or blown components.

At first I thought I had found a clue when I connected my multimeter to look at VCC of ICB801S. I saw about 15V AC. To get a closer look I connected my scope and I am seeing see -150VAC rectified which makes absolutely no sense. Every component in this part of the circuit should be blown to bits! Not sure why I was seeing 15V AC except maybe because it was not a pure sine wave was throwing off my cheapie meter.
Are the power supplies running a floating ground?

Look at the schematic of almost any SMPS. The AC input goes through a multi-stage noise filter, then to a bridge rectifier. The output of the bridge goes to a filter cap. Each side of the filter cap is swinging about 166 volts with respect to chassis ground - the positive side swings from 0 volts to +166 volts; the negative side swings from -166 volts to 0 volts. That is why that portion of the power supply board is labeled HOT.

If you are going to use a scope to check anything on the hot portion of the board, use an isolation transformer.

PlainBill

[Toasty]

Re: Samsung Syncmaster 245BW

Pull the connector between the video board and the inverter -at- the video board. Try powering up. If 24v can be measured there, the problem is in the inverter.

[danweil]

Re: Samsung Syncmaster 245BW

I have a 245B . This week it started making a constant clicking sound as if a fan was running badly, clicking multiple times second. Otherwise it works fine (except for a loud crack every now and then as if plastic is expanding but it has been doing that ever since I bought it). I called Samsung but it is over 3 years old, and they told me it is most likely the power supply. I have opened it up and found no fan or obvious problem on the PSU and then found this forum and read through 19 pages without finding any similar problem. is it the beginning of the one of the problems in this forum or has anybody and other idea what is could be

[dbinokc]

Re: Samsung Syncmaster 245BW

I did a little more checking last night before the replies were posted. I checked a few components. At first I thought the problem was at DB871. I pulled the component and the diode tested good. I suppose it could have problems with breakdown Next I pulled ICB801S thinking maybe the 292V going in at pins 4 and 5 had blow through the chip somehow and was making it to pin 7. Looking at pin 7 showed the same waveforms as before.
I saw the comments about RB807,RB806 and RB805 sometimes failing. I ohmed out those resistors. I did find one open. (Never seen an open resistor before. They usually burn or blow up) I replaced that one, but still no change. I will recheck the other two this evening in case they opened up while I was replacing the first one.

Based on the -150VAC, I started thinking maybe I had a bad diode further up stream. and started probing. I could not find anything definitive.

Plain Bill,
Are you suggesting using the isolation transformer for safety reasons or to eliminate the -160VAC ?

Danweil,
I will try your suggestions this evening.

[PlainBill]

Re: Samsung Syncmaster 245BW

I have a 245B . This week it started making a constant clicking sound as if a fan was running badly, clicking multiple times second. Otherwise it works fine (except for a loud crack every now and then as if plastic is expanding but it has been doing that ever since I bought it). I called Samsung but it is over 3 years old, and they told me it is most likely the power supply. I have opened it up and found no fan or obvious problem on the PSU and then found this forum and read through 19 pages without finding any similar problem. is it the beginning of the one of the problems in this forum or has anybody and other idea what is could be

I'd suspect a problem with the backlights, but that's really only a guess.

The best idea would be to open it up and use a cardboard tube - such as the center from a roll of paper towels - as a crude stethoscope to determine where the sound is coming from. After that, attach pictures and we can make suggestions that have a better chance of being correct.

PlainBill

[dbinokc]

Re: Samsung Syncmaster 245BW

Danweil,
I will try your suggestions this evening.

Sorry, I meant Toasty, not Danweil

[Toasty]

Re: Samsung Syncmaster 245BW

Dbinokc & Danweil - the BN44- # of the power supply please.

[danweil]

Re: Samsung Syncmaster 245BW

I took a photo before rebuilding it. unfortunately I haven't got a perfect picture of the BN but reads like BN44-00173A, whereby the 4-00173A is readable, ( the 00 and 3A in this string are clearly visible)

[Toasty]

Re: Samsung Syncmaster 245BW

Then yours is the one with the 3 resistor problem.

[danweil]

Re: Samsung Syncmaster 245BW

.. and thanks PlainBill for the suggestion with the stethoscope. I'll try that . the sound seems to be coming from the PSU but I couldn't see how to isolate the noise (which is louder when a PC picture signal is on, relative to just power on). I guess photos are required of the component side of the PSU board ? I have tried recording the sound but the transformer sound swamps the clicking sound on the recording, it's clicking about 10 times a second or more

[Toasty]

Re: Samsung Syncmaster 245BW

It's the PSU trying to start and failing. If the caps are bad and/or the resistors, it will do that. I think someone on eBay sells the repair kit for that model PSU.

[dbinokc]

Re: Samsung Syncmaster 245BW

The number on mine is BN44-0173A as well.

[Toasty]

Re: Samsung Syncmaster 245BW

Found it:

http://www.ebay.com/itm/330582684088

Repair Kit, Samsung SyncMaster 245BW, LCD Monitor, Caps

$16.95 and includes the 3 resistors

Seller: sghill99

Not a recommendation of the seller. Just what I found.

[danweil]

Re: Samsung Syncmaster 245BW

Thanks for all the suggestions. Note the monitor works but just makes this annoying fan type noise

I opened up box again, took a number of pictures, and got it up and working with the whole thing dismantled. We took a cardboard tube and listed. 2 of us couldn't really locate the noise, only generally. Using a a doctors stethoscope we concurred that it seems to be the white "2J 6843, SIC 460S (on the board is written CP801)" but we could have been mistaken and our next bet was one of the blue units in the direction of the fuses

written on the S/n sticker is written Rev 1.1, BN44-00173A. and I attach pictures.

I should try just replacing the 3resistors first I assume rather than all the potential damaged parts. 68 ohm 2watt (or 5 watt)

[dbinokc]

Re: Samsung Syncmaster 245BW

I found one bad resistor in the 3 on my board. Before removing and/or ordering you may want want to check them on the board with a multimeter first. They should each read 68 ohms. The bad one on my board read as an open.

[PlainBill]

Re: Samsung Syncmaster 245BW

Thanks for all the suggestions. Note the monitor works but just makes this annoying fan type noise

I opened up box again, took a number of pictures, and got it up and working with the whole thing dismantled. We took a cardboard tube and listed. 2 of us couldn't really locate the noise, only generally. Using a a doctors stethoscope we concurred that it seems to be the white "2J 6843, SIC 460S (on the board is written CP801)" but we could have been mistaken and our next bet was one of the blue units in the direction of the fuses

written on the S/n sticker is written Rev 1.1, BN44-00173A. and I attach pictures.

I should try just replacing the 3resistors first I assume rather than all the potential damaged parts. 68 ohm 2watt (or 5 watt)

All three of the components you identified is a capacitor, but they are not electrolytic caps, and are much less likely to fail.

I can do a tentative identification of them.

The white one is a .68uF film cap; I'd guess that the voltage would be 450 volts. A POSSIBLE replacement would be a Panasonic ECW-F2W684JA, Digikey P14204-ND at $.96.

The blue ones are .33uF, 275VAC EMI suppression caps. A possible replacement would be Panasonic ECQ-U2A334ML, Digikey P10733-ND at $.57.

In each case, additional information would be desirable before ordering. The lead spacing is critical, and it would be very nice to know the voltage rating of CP801 (it may be printed on the side).

The three 68 ohm resistors are another issue. They are a common failure on this power supply. If one of them goes open, the supply won't work. I'd agree that replacing them would be a good idea, even though it won't help with the noise problem.

I should note that while it is possible to positively identify proper replacement for the suspect parts, they are only suspect - there is an excellent chance that none of them are the source of the noise.

PlainBill

[Toasty]

Re: Samsung Syncmaster 245BW

@ danweil -
Above the white capacitor you identified, mounted on the aluminum heatsink with the 's on it, are the main switchers for this unit. On the legs of them are ferrite beads. While the unit is running, use a plastic or wooden stick to touch those beads one at a time and see if the noise goes away. The goop that the factory uses may have dried up allowing them to vibrate.

The 10x a second sound does seem to me that the startup caps are beginning to fail however. Before you put it back together, I would invest in the repair kit mentioned, and recap that board. Like changing the tires before they've lost all their tread and now you're on the rainy highway trying to stop...

@ dbinokc -
Any results?

[danweil]

Re: Samsung Syncmaster 245BW

Thanks very much for your insights- I am very impressed . "Toasty" Since we also considered that the noise source was the heatsink on first examination but then thought that it can't generate noise since it is just a heatsink that sounds like it might be the issue. So I'll try the wooden stick approach that next time I take it apart (to replace the 3 resistors)- the ferrite beads are pretty small I assume. If it works I guess I need some goop, e.g non conductive something to stop the movement, what can a layman use, the goop that is used to seal tiles and baths etc or has it got to be some special plastic dip. "Plainbill": I will also try and see if the 2J 6843 (next to the CP801 label) has any additional labeling.

Living in Germany means that I would have to wait some time for the kit so I want to try the simple methods first, the cap heads look really good. Also I surely increase the probability of doing something wrong by replacing all the electrolytic caps

p:s and if I do change loads of components is there any thing I can do to reduce the general noise level. The PSU general background hum is loud in comparison with other monitors

I will write back after trying wooden stick/ 3 resistors approach- won't be for another week or so when I get some time