Samsung Syncmaster 931BW - No Power

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Hello, I'm back with the measures

According to the circles made by Plainbill, I name from "a" at the top left, to "d" at the top right pin. I'm sorry, I can't tell colours apart (I'm partly colour blind). I guess yellows on the left (Rab), and orange on the right (Rcd).

Rab = 3.197k Ohm
Rbc = 221,2k Ohm (parallel to the also noted "R31" on the board)
Rcd = 1.136k Ohm
I could also unsold the transformer if needed.

Obviously, values don't match in the 3% range. So I guess the transformer is bad. I let your wise confirm it !

If you could also explain me why the resistance can change (I would say it is either good or open circuit), I'm also interested in that

Thanks,

renArD

The values are definitely different, one winding is bad. Replace the transformer. The TMS92515CT is available from several sellers on eBay.

There are two possible reasons for a change in resistance. the most common is a short between adjacent layers of windings. This will reduce the resistance. The other is a break in a winding. This results in an increase in the resistance.

PlainBill

[Panther]

Re: Samsung Syncmaster 931BW - No Power

The values are definitely different, one winding is bad. Replace the transformer.
PlainBill

Are you sure? Wouldn't want to go blindly replacing a transformer. That'd be just plain foolish.

The TMS92515CT is available from several sellers on eBay.
PlainBill

Really? Now why didn't anyone else mention eBay? Oh wait...

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Are you sure? Wouldn't want to go blindly replacing a transformer. That'd be just plain foolish.



Really? Now why didn't anyone else mention eBay? Oh wait...

Well, I've found that some people make mistakes when measuring resistances. I note the OP made three resistance measurements while I only asked for two, that does tend to reduce one's confidence slightly. As far as suggesting eBay, I've found that Googling a part number tends to give good results.

Yes, you were right. Why don't you give me your address?? I'll send you a 'Genius' sign that you can wear so you will get the attention you need.

PlainBill

[Panther]

Re: Samsung Syncmaster 931BW - No Power

Yes, you were right. Why don't you give me your address?? I'll send you a 'Genius' sign that you can wear so you will get the attention you need.

PlainBill

From all the great help you've given many people on this forum I'd say you're easily much closer to being a genius than me. You are truly very knowledgable.
Trouble is you can also be very condescending, self righteous and even plain mean to some people. Heaven forbid if they don't use correct punctuation or do something else you deem wrong.

Anyway, you'll be happy to know that you won't be hearing from me on "your" forum any more.

To the OP and renard-ad, I hope you're successful in repairing your respective monitors and I apologise to having resorted to a slinging match in your thread.

[renard-ad]

Re: Samsung Syncmaster 931BW - No Power

Thank you for your replies ! I ordered a new transformer and I'm waiting for it. I'll let you know when there is something new.
Thank you also for the wrong resistance explanation.

Dear Panther, I'm pretty sure that - when quoting you're "it may be the transformer" message - Plainbill didn't want to correct you but he wanted to warn me not to misread what you actually said (it may be). As I'm a newbie, I could have rejoiced too fast. So it wasn't a correction about what you wrote but a delicate attention for me not to fall in the "recipe that works". So thank you Panther for sharing your previous experience on a LCD monitor. You're help is appreciated !
When Plainbill says to replace the transformer and have a look on ebay, you could also personally consider you guessed right and be happy that your solution is the solution. However, giving help on forums is not a race.

In my own experience I've been facing many wrong interpretation of written messages because we lack usual information (that we have in voice and physical expression). Maybe Plainbill is as you said, but maybe he only tries to give advices without being emotionally involved. That may appear like "I don't care, I'm above all that so easy problems" but we'd better notice the patience and perseverance for helping so many people. Indeed, if I understood well, my problem is quite obvious in the LCD field but he took the time to check step by step what is the real cause in order not to needlessly change all components (this would have been easier for him to advice to change all !).

At all events, I'm thankful for both of you for taking time to give me escape doors to my problem. For now I don't know if replacing the transformer will be enough, but we walk side by side to the solution. Thanks all for sharing your knowledge !

renArD

[renard-ad]

Re: Samsung Syncmaster 931BW - No Power

Dear all,

I finally received the transformer ! And it works well :-D

Thanks a lot for all your personalized help and your patience !

I hope this thread may help someone else.

renArD

[aliens]

Re: Samsung Syncmaster 931BW - No Power

Hey,

I have a very similar problem as Glennjamin, only it's with a 931C instead of 931BW. The electric boards are 99% the same.

My problem started with slow starts, led button flickering for like 10 minutes (longer if I system was shut down over night) before starting up. My bad was not fixing the issue right away, and instead I waited like 2 months until a few days ago, when the led button wouldn't light up at all, as it would be unplugged. I opened it, replaced the bad caps (2 820u and 1 470u), which would probably fix the flickering issue, but I still have no power at the led button.

I got my multimeter and traced the steps Glennjamin did here, and I have his exact same values up until his last post. Anywhere to go from there? I wish I knew if he fixed it and how.

Cheers!
Mike

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Hi Mike,

I got an automatic email saying someone had replied to this thread. Just so you know I still have the monitor in pieces under my bed, I couldn't resolve the problem despite getting the power board up and working.

Not sure what similarities the 931C and 931BW have but possibly we could possibly be looking at an identical problem.

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Hey,

I have a very similar problem as Glennjamin, only it's with a 931C instead of 931BW. The electric boards are 99% the same.

My problem started with slow starts, led button flickering for like 10 minutes (longer if I system was shut down over night) before starting up. My bad was not fixing the issue right away, and instead I waited like 2 months until a few days ago, when the led button wouldn't light up at all, as it would be unplugged. I opened it, replaced the bad caps (2 820u and 1 470u), which would probably fix the flickering issue, but I still have no power at the led button.

I got my multimeter and traced the steps Glennjamin did here, and I have his exact same values up until his last post. Anywhere to go from there? I wish I knew if he fixed it and how.

Cheers!
Mike

There is come confusing terminology in your post. Do you have the correct voltages out of the power supply? If you do, I'd like to see a good picture of the signal board. One possibility is the contents of the program EEPROM became corrupted by the unstable voltages.

PlainBill

[aliens]

Re: Samsung Syncmaster 931BW - No Power

There is come confusing terminology in your post. Do you have the correct voltages out of the power supply? If you do, I'd like to see a good picture of the signal board. One possibility is the contents of the program EEPROM became corrupted by the unstable voltages.

PlainBill

Here are some pics. First is the whole assembly ip board -> main board -> function PCB/power button. The following are the ip board, main board and function pcb with measurements done as Glennjamin did. Last is with the bad caps I replaced.

I also found the service manual here:

http://www.givemefile.net/smanuals/m...ile/37458.html

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Here are some pics. First is the whole assembly ip board -> main board -> function PCB/power button. The following are the ip board, main board and function pcb with measurements done as Glennjamin did. Last is with the bad caps I replaced.

I also found the service manual here:

http://www.givemefile.net/smanuals/m...ile/37458.html

I'm not sure what the problem is.You have established that the LDO regulators are working properly. There are three 8 pin ICs, one has write enable held off, that would be the program memory, so the chances it is corrupt are greatly reduced. The is no reset controller, so we can eliminate that possibility. Remember that the power LED is controlled by the GPU.

The best advice I have at this point is trying to reinitialize the monitor. I haven't found any information for this monitor, but the process goes something like this. Unplug the monitor, hold down several of the control buttons (I don't know which ones) plug in AC power, wait 3 seconds and release the buttons. Most monitors have 5 buttons - that yields 31 possible combinations.

PlainBill

[aliens]

Re: Samsung Syncmaster 931BW - No Power

I'm not sure what the problem is.You have established that the LDO regulators are working properly. There are three 8 pin ICs, one has write enable held off, that would be the program memory, so the chances it is corrupt are greatly reduced. The is no reset controller, so we can eliminate that possibility. Remember that the power LED is controlled by the GPU.

The best advice I have at this point is trying to reinitialize the monitor. I haven't found any information for this monitor, but the process goes something like this. Unplug the monitor, hold down several of the control buttons (I don't know which ones) plug in AC power, wait 3 seconds and release the buttons. Most monitors have 5 buttons - that yields 31 possible combinations.

PlainBill

Tried all combinations, no joy. I noticed that, when the monitor is plugged in, there's a very faint voltage sound coming from the ipboard/logic board. When I press the menu/brightness/etc buttons the sound slightly shifts higher or lower, which I guess it means that the buttons should be working, yet there's still no(t enough?) power.

Cheers

[aliens]

Re: Samsung Syncmaster 931BW - No Power

One thing though, the service manual (pdf 7) says I should have 5V on the 9th pin on the ip board -> logic board connectors, yet somewhere else it says that 0V should be for the ON status. I have 0V as well, (though as I mentioned, I do have 15V on pin 2 and 5V on pin 6 and 7). Would this be an issue?

[alexanna]

Re: Samsung Syncmaster 931BW - No Power

One thing though, the service manual (pdf 7) says I should have 5V on the 9th pin on the ip board -> logic board connectors, yet somewhere else it says that 0V should be for the ON status. I have 0V as well, (though as I mentioned, I do have 15V on pin 2 and 5V on pin 6 and 7). Would this be an issue?

Samsung power supplies are usually very good about listing pin voltages going to the signal board. What are they listed as, and what do you read?
Are the voltages you are reading on pins 2,6 and 7 steady ?

[aliens]

Re: Samsung Syncmaster 931BW - No Power

Samsung power supplies are usually very good about listing pin voltages going to the signal board. What are they listed as, and what do you read?
Are the voltages you are reading on pins 2,6 and 7 steady ?

I'm not home right now to make a print of the troubleshooting page of the manual (but you can see it in pdf 931C[7] from the service manual archive I linked in one of my previous posts), but in it it states that, on CN600 (the connector on the logic board that connects to the IP board), pin 2 should be 15V, pin 7,9 should be 5V. My tests show 15V on pin 2, 5V on pin 7 (and 6), but 0V on pin 9.

The second picture attached in my previous post shows this (although that is the IP board).

[aliens]

Re: Samsung Syncmaster 931BW - No Power

Here's the PDF that includes the "No Power" troubleshooting guide.

[aliens]

Re: Samsung Syncmaster 931BW - No Power

After a bit more testing, the 5V on pin 6&7 and 15V on pin 2 are solid (no fluctuations). On pin 9 there's 0.141V constantly. Next to it it says On/Off, and the manual says that On is 0V (but as I mentioned, it says that during testing it should be 5V).

[alexanna]

Re: Samsung Syncmaster 931BW - No Power

I suspect a misprint in the manual,Usually at least all I have noticed the on/off voltage 3 volts or higher when the logic board requests back lights.
Would you mind re-testing the voltage regulators,they can cause problems. And they must be within 1% of the rated specification.

[aliens]

Re: Samsung Syncmaster 931BW - No Power

I suspect a misprint in the manual,Usually at least all I have noticed the on/off voltage 3 volts or higher when the logic board requests back lights.
Would you mind re-testing the voltage regulators,they can cause problems. And they must be within 1% of the rated specification.

As seen in the picture (from left to right):

IC602: 3.8V 1.8V 0V and 1.8V on the bottom
IC601: 5.15V 3.3V 0V and 3.3V on the bottom

[alexanna]

Re: Samsung Syncmaster 931BW - No Power

Those voltages are some common voltages we see.
One thing to think about the flow chart you're looking at is for no power, you actually have power.
The front power LED is not turning on and 0 volts on the Back light on pin indicates that the logic board is not asking for back lights to be on.
One other simple test would be to verify that on/off pin on the front panel switch changes state as the power button is pushed. Usually this starts out as a high voltage and goes low when the power button is pushed.