Samsung Syncmaster 931BW - No Power

[Glennjamin]

Hi there,

I'm a little of a novice with this kind of thing but I've been doing a lot of reading here and other sites to get up to speed.

Got this monitor from a friend, no power at all when plugged in, no flashing power button light. Nothing! Opened up the monitor, the power board had 3 bulging caps. Replaced them, tested - no change. Replaced all the other caps (not bulging, with exception of the big 100uf 450v one), retested - no change.

Need some advice on what to check next? I'm not even certain if the power button works? What else should I look at? (I have borrowed a hilix DT-830b multimeter.)

Any advice would be great! Thanks

[sam_sam_sam]

Re: Samsung Syncmaster 931BW - No Power

Please post some photo of your monitor power and control boards

Did you check any of the fuses that are on the power board

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

3sam's advice is correct. It's hard to provide advice when you can't see what you are dealing with.

In general, I try 2 quick tests.

1. CAREFULLY!!! measure the DC voltage across the mains filter cap. It should read about 1.4 x the mains voltage - 165 volts if you live in the US or Canada.

2. If the first test gives the correct voltage, measure the voltage from a power supply mounting screw to each of the power supply outputs. Report those voltages with your the pictures.

PlainBill

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Thanks for the replies, pictures attached below (overall image of power board, then two closer pictures).

I live in London in the United Kingdom, PlainBill. Wikipedia says it's 230V here. Is that right?

1. This this the brown cylindrical component next to the mains adapter?

2. I see the mounting screw, but there seems to only be one power output (the white plug, top right corner of pic), is this OK?

Much of this is new to me but I'm enjoying learning, please bare with me!

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Thanks for the replies, pictures attached below (overall image of power board, then two closer pictures).

I live in London in the United Kingdom, PlainBill. Wikipedia says it's 230V here. Is that right?

1. This this the brown cylindrical component next to the mains adapter?

2. I see the mounting screw, but there seems to only be one power output (the white plug, top right corner of pic), is this OK?

Much of this is new to me but I'm enjoying learning, please bare with me!

Oh, this is going to be a training session. Maybe I should bookmark this...

I've labeled a few of the components. The part you had mentioned is the mains input fuse. Hint: There is a system for component identifiers. C101 would be a capacitor, F101 would be a fuse, D is for diode, T is for transformer, CN denotes a connector, R is for resistor, and Q is for Transistor.

The first step would be to set the DMM to the 1000 VDC range and carefully measure the voltage across the leads of the Mains Filter Capacitor. This should be about 320 volts, so be careful. A voltage 10-20 volts higher or lower does not represent a problem, a voltage of less than 10 volts indicates the fuse has blow or the power cord is not plugged in. Report those results

If you measured the proper voltage, reset the DMM to 20VDC. If you notice the output connector, the function of each of the pins is identified. Hold the black lead on one of the pins labeled GND and measure the voltage on the pins labeled (I think) 5.2V and 15V. Report those results.

PlainBill

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Heh, thank you for the quick run down, I do apologise for missing the word 'cap', I thought I had grasped the concept of capacitors. I guess not quite yet.

The first step would be to set the DMM to the 1000 VDC range and carefully measure the voltage across the leads of the Mains Filter Capacitor. This should be about 320 volts, so be careful. A voltage 10-20 volts higher or lower does not represent a problem, a voltage of less than 10 volts indicates the fuse has blow or the power cord is not plugged in. Report those results

OK fine, I shall do that. To check I'm not being ignorant, I do this with the power board unplugged? I'm taking that default action for safety sakes, but I believe I may be wrong.

Hold the black lead on one of the pins labeled GND and measure the voltage on the pins labeled (I think) 5.2V and 15V. Report those results.

PlainBill

Understood. Yes near enough, 5.1V and 15V it says. I'll report back shortly, thanks again.

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Heh, thank you for the quick run down, I do apologise for missing the word 'cap', I thought I had grasped the concept of capacitors. I guess not quite yet.
OK fine, I shall do that. To check I'm not being ignorant, I do this with the power board unplugged? I'm taking that default action for safety sakes, but I believe I may be wrong.

Understood. Yes near enough, 5.1V and 15V it says. I'll report back shortly, thanks again.

You were wrong. Do the tests with the power board on a nonconductive surface, the signal board disconnected, and the power cord plugged in.

PlainBill

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

OK the results for the large cap, tests at about 332V. So I assume that seems fine.

I can't get a reading whatsoever on the output connector. Black on GND, red on 1.5V pin or 5.1V pins (2 of them), nothing whatsoever.

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

OK the results for the large cap, tests at about 332V. So I assume that seems fine.

I can't get a reading whatsoever on the output connector. Black on GND, red on 1.5V pin or 5.1V pins (2 of them), nothing whatsoever.

That's good, it tells us that the power supply is the problem. We can fix most things that go wrong with a power supply. Fixing the signal card can be much harder.

Your next mission is to take a picture of the back of the power supply. When you take the picture, make sure the mains power connector is closest to you, just like the picture of the top. That makes tracing signals easiest. Also, what is the part number of IC101 (it's attached to the heat sink).

PlainBill

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Pictures attached, did my best with artificial light as it's quite late here now. I hope you can make them out otherwise I will do them again in the morning.

RE: IC101, the writing on the side of it is as follows -

F DH15
E
DM0465R

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Pictures attached, did my best with artificial light as it's quite late here now. I hope you can make them out otherwise I will do them again in the morning.

RE: IC101, the writing on the side of it is as follows -

Bingo!!! FSDM0465RB is a Fairchild Power Switch integrated SMPS controller and power FET. The datasheet is here. Use the datasheet to identify the pin numbering scheme, then CAREFULLY measure the voltage from pin 2 to pin 3.

PlainBill

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

10.70V between those two pins (GND and Vcc). Not sure what this means for the FPS.

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

10.70V between those two pins (GND and Vcc). Not sure what this means for the FPS.

Aww, fudge!! It's in a gray area.

Here's a quick explanation. Pin 6 is connected to the filtered mains voltage. Internally there is a constant current source that charges the startup cap - C107 until the voltage on pin 3 rises to 11 to 13 volts. At that point the SMPS controller goes active and starts driving the power FET, which generates the proper output voltages.

This design is used by various manufacturers. There are two failure modes. in one, the cap goes bad. This is usually characterized by a pulsing output - the 5.1 and 15V outputs show short bursts of voltage; often a faint ticking sound can be heard every few seconds. In the second, the IC itself degrades to the point the voltage across the cap does not reach the startup threshold.

My recommendation is to observe the pin 2 - pin 3 voltage carefully. If it appears steady, replace the IC. It is available from a number of sellers on eBay.

If it varies, replace the cap. If you really like this monitor, serious consideration should be given to replacing all the electrolytic caps on the power supply / inverter.

PlainBill

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Right ok, thank you for the explanation. Before I started down this route I listened for ticking and never heard any which makes sense. I measured pin 2 and 3 over time (couple of minutes) and it was hugely consistent, only fluctuating 0.01V here and there. This leads me down the road to replace the IC. Searching "Fairchild Power Switch" on ebay yields varieties with only 4 or 5 legs (mine has 6), am I searching the correct term?

RE: caps, as I said in the first post I have now replaced all the caps on the board with exception of the mains filter cap, which we tested earlier to be good I believe. The inverter board seems to have nothing I can replace! Image attached, thanks.

edit: Starting to find some success on ebay with the 6 legged version. Does it have to be the exact same model, DM0465R?

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Right ok, thank you for the explanation. Before I started down this route I listened for ticking and never heard any which makes sense. I measured pin 2 and 3 over time (couple of minutes) and it was hugely consistent, only fluctuating 0.01V here and there. This leads me down the road to replace the IC. Searching "Fairchild Power Switch" on ebay yields varieties with only 4 or 5 legs (mine has 6), am I searching the correct term?

RE: caps, as I said in the first post I have now replaced all the caps on the board with exception of the mains filter cap, which we tested earlier to be good I believe. The inverter board seems to have nothing I can replace! Image attached, thanks.

edit: Starting to find some success on ebay with the 6 legged version. Does it have to be the exact same model, DM0465R?

The full part number is FSDM0465RB. Many times it is abbreviated to the numbers on the IC, DM0465R. There are several auctions in Great Britain. This auction also looks good, you get two, but shipping could take a while; I'm not sure about import duties. There are also several higher current variations, I don't think it is worthwhile to upgrade.

PlainBill

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Searching DM0465R seems to have been more fruitful, I'll order one of these and post back to update the thread in the near future. Your help has been much appreciated!

[renard-ad]

Re: Samsung Syncmaster 931BW - No Power

Dear Glennjamin, I'm new in this forum and I would like to thank you for your usefull post. I would also like to say you're not alone to face this problem

Dear PlainBill, I'm really impressed by all your technical advices. Thanks a lot for sharing your knowledge !

I'm looking forward to have some news from Glennjamin with the idea of changing the DM0465R.

In the meantime, I dare to share my similar problem. I'm not sure of the case I facing to (according to the following citation from PlainBill).

This design is used by various manufacturers. There are two failure modes. in one, the cap goes bad. This is usually characterized by a pulsing output - the 5.1 and 15V outputs show short bursts of voltage; often a faint ticking sound can be heard every few seconds. In the second, the IC itself degrades to the point the voltage across the cap does not reach the startup threshold.

When I measure the 5V pin or 15V pin on my (very old) oscilloscope, they seem to be flat. When I measure them with a DC multimeter, they are 5V and 18V. And when I use AC multimeter, 5V pin is 0V fluctuation also 15V pin has 31V bursts (about 2 or 3 by second). So I thought I was in the first case : "pulsing output : cap goes bad" (but which one ?). Moreover, there is a "zzz" sound (the inductance ?) a first time and 15s after (and then, seems not to happen again). During this buzzz, the 18V goes down to 15V. When the monitor is off, it is 15V.

But, on the other side, I observed the voltage between pins 2 and 3 of the DM0465 with DC multimeter (hard to use oscilloscope due to ground referencing). It is 14.5V (but 11.3V when monitor is off) which seems to be too high (according to "11 to 13V"). With AC multimeter it is very fluctuating.

The voltage is not steady but maybe not the good value in DC too. I understood that PlainBill advised an IC changing. Indeed, I changed some caps and it didn't change anything (apparently).

Well, I don't know if in that case I should change IC and/or caps, and which ones. It seems to be a failure when current is asked only (monitor on) because otherwise (monitor off) it seems ok. Adding extra caps, for an eventual current transition, didn't help.

Please note the version of my PCB is quite different (I hope I can post photos soon). I apparently have no "C107" cap. Which one would it be on the datasheet's first page ("typical flyback application") ?

Thanks a lot,

renArD
PS : sorry for poor English :-(

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Dear Glennjamin, I'm new in this forum and I would like to thank you for your usefull post. I would also like to say you're not alone to face this problem

Dear PlainBill, I'm really impressed by all your technical advices. Thanks a lot for sharing your knowledge !

I'm looking forward to have some news from Glennjamin with the idea of changing the DM0465R.

In the meantime, I dare to share my similar problem. I'm not sure of the case I facing to (according to the following citation from PlainBill).

When I measure the 5V pin or 15V pin on my (very old) oscilloscope, they seem to be flat. When I measure them with a DC multimeter, they are 5V and 18V. And when I use AC multimeter, 5V pin is 0V fluctuation also 15V pin has 31V bursts (about 2 or 3 by second). So I thought I was in the first case : "pulsing output : cap goes bad" (but which one ?). Moreover, there is a "zzz" sound (the inductance ?) a first time and 15s after (and then, seems not to happen again). During this buzzz, the 18V goes down to 15V. When the monitor is off, it is 15V.

But, on the other side, I observed the voltage between pins 2 and 3 of the DM0465 with DC multimeter (hard to use oscilloscope due to ground referencing). It is 14.5V (but 11.3V when monitor is off) which seems to be too high (according to "11 to 13V"). With AC multimeter it is very fluctuating.

The voltage is not steady but maybe not the good value in DC too. I understood that PlainBill advised an IC changing. Indeed, I changed some caps and it didn't change anything (apparently).

Well, I don't know if in that case I should change IC and/or caps, and which ones. It seems to be a failure when current is asked only (monitor on) because otherwise (monitor off) it seems ok. Adding extra caps, for an eventual current transition, didn't help.

Please note the version of my PCB is quite different (I hope I can post photos soon). I apparently have no "C107" cap. Which one would it be on the datasheet's first page ("typical flyback application") ?

Thanks a lot,

renArD
PS : sorry for poor English :-(

The voltage reading between pins 2 and 3 indicates the SMPS controller is working. The variation on the 15V line would indicate replacing the filter caps on that power rail would be a good idea. In general, I am of the opinion that if a monitor contains inferior caps (Capxon, Lelon, Elite, and countless other brands), the best procedure is a complete recap.

PlainBill

[renard-ad]

Re: Samsung Syncmaster 931BW - No Power

Thanks ! I'll try and let you know (unfortunately not immediately but within a few weeks I guess).

renArD

[renard-ad]

Re: Samsung Syncmaster 931BW - No Power

If it can help anyone :
- I upload two photos of the version I have
- This version of the board (PWI1904SJ A Rev 1.0) seems to be also used in the Samsung Syncmaster 940NW.
- Here is the list of the original caps :
* "100uF 450V" for C101
* 3x "470uF 25V 105°C brand JH" for C31, C202, C201
* "1000uF 16V 105°C brand JH" for C205
* 2x "330uF 25V 105°C brand JH" for C203, C206
* "1uF 50V 105°C brand JH" for C204

Regards