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LCD Monitor Power Supply board connections (Samsung IP-35155A)

 
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The backstory:

We had a "power issue" here a few days ago and now our Samsung SyncMaster 931b is not working. The blue power light around the button flashes and every second or so the display will flicker with light and you can briefly (for 200ms or so, I'd guess) see the display.

From what I gather, this is due to a voltage flicker through the transistors in the power supply tricking the monitor into thinking it's being shut down so I take it apart and notice three swollen caps on the power supply board (Samsung IP-35155A, components C113, C112, C316, 470uF 25V, 820uF 25V and 820uF 25V, respectively). I figure those are what are feeding the transistors and they're hosed and it's screwing with the operation of the monitor. A capacitance check of each shows about 16uF. Bad caps; I'll get some more from DigiKey and replace them and hopefully that fixes the flicker problem.

The new issue:

I guess I wasn't paying too much attention when I took it apart so I'm wondering where everything goes. I think C113 is the 470uF and the other two are the 820uF caps, but I'm not sure. Can anyone verify that?

Also, I wasn't paying attention to where the connectors for CN301, CN302, CN0303 and C304 went. They all have the same wire colors, are all the same keying, etc. and they are grouped into sets of two which have heat shrink around them so I can't tell where they go. The picture here shows a simple diagram with the connectors marked with a red box. What are these connectors for and how should they be hooked up? Is it just lamp power? Does it make a difference if CN301 and CN302 are switched and/or CN303 and CN304 are switched?

 
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Donald,
your problem sounds exactly the same as what happened to me. Don't even tell me that the cause was wires falling from poles in a neighbors back yard. OK the reason I'm posting:
1. C113 is the 470uf C112 and C313 are the 820uf caps.
2. Were you able to repair the problem?
Tom Cook

The backstory:

We had a "power issue" here a few days ago and now our Samsung SyncMaster 931b is not working. The blue power light around the button flashes and every second or so the display will flicker with light and you can briefly (for 200ms or so, I'd guess) see the display.

From what I gather, this is due to a voltage flicker through the transistors in the power supply tricking the monitor into thinking it's being shut down so I take it apart and notice three swollen caps on the power supply board (Samsung IP-35155A, components C113, C112, C316, 470uF 25V, 820uF 25V and 820uF 25V, respectively). I figure those are what are feeding the transistors and they're hosed and it's screwing with the operation of the monitor. A capacitance check of each shows about 16uF. Bad caps; I'll get some more from DigiKey and replace them and hopefully that fixes the flicker problem.

The new issue:

I guess I wasn't paying too much attention when I took it apart so I'm wondering where everything goes. I think C113 is the 470uF and the other two are the 820uF caps, but I'm not sure. Can anyone verify that?

Also, I wasn't paying attention to where the connectors for CN301, CN302, CN0303 and C304 went. They all have the same wire colors, are all the same keying, etc. and they are grouped into sets of two which have heat shrink around them so I can't tell where they go. The picture here shows a simple diagram with the connectors marked with a red box. What are these connectors for and how should they be hooked up? Is it just lamp power? Does it make a difference if CN301 and CN302 are switched and/or CN303 and CN304 are switched?

 
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Also the Pairs with the pink wires go toward the center of the board (CN302 & CN304)
The pairs with the blue wires go to the outside plugs (CN301 & CN303)
Tom Cook

 
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Donald,
your problem sounds exactly the same as what happened to me. Don't even tell me that the cause was wires falling from poles in a neighbors back yard. OK the reason I'm posting:
1. C113 is the 470uf C112 and C313 are the 820uf caps.
2. Were you able to repair the problem?
Tom Cook

Tom, thanks for clearing up the cap locations. Did you mean C316 rather than 313 though? You almost nailed the power situation: All of this is going on at work and we had a car hit a power pole down the street and it knocked out one of the phases for a while so we were half-a**ed operating on single-phase electricity for a while, which is what I think caused the problem, then the power was out totally for a while, then when it came back on the monitor had the flicker thing going on. I'm pretty disappointed that it even happened as most/all of our equipment is attached through APC ES550s.

We haven't got the new caps in from DigiKey yet, so I haven't repaired it. I tried cobbling up caps with similar capacitance from ones we had here in series/parallel, but I think my some of my EE know-how must have escaped me because that didn't work out. Did you manage to fix yours?

Any idea on what connectors CN301,CN302, CN303 and CN304 are, how they are hooked up or if it matters if they are switched around?

ETA: Saw post regarding these connections. Thanks!

 
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Oops, I may have spoken too soon about the connectors at CN***. I don't have pink vs blue wires. All four connectors have one fat light-blue conductor and one skinny black conductor running to them. :-O

 
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Donald,
I guess we're talking about different but very similar power hits. I overlooked the tops of the caps being pushed up, but the same three are up on my board. I ordered them from a local supplier, they will be in in about a week. Thanks for focusing me on what I overlooked!
Tom

 
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Donald,
I guess they must use this board on a wide variety of monitors. I was just looking at the other google results (that's how I got here). There is a seller on E-Bay that has 10 of these boards for sale for $40 + $15 shipping a copy. If this doesn't work that may be a possible solution.
Tom Cook

 
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Donald,
I guess they must use this board on a wide variety of monitors. I was just looking at the other google results (that's how I got here). There is a seller on E-Bay that has 10 of these boards for sale for $40 + $15 shipping a copy. If this doesn't work that may be a possible solution.
Tom Cook

I found quite a few IP boards on eBay as well as a number of Asian electronics retailers that had the same model number as the one I have but when you look at the board layout it's in a totally different configuration. I'm not sure if the different layouts would still work since they have the same model number but the main differences that I saw were the addition/lack of several capacitors, resistors and heatsinks. From what I could tell though, it looked like the connections to the board were the similar, if not the same.

 
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Well, I replaced the caps today and put the thing back together (correctly? fingers crossed).

Still not functioning correctly. The blue power light stays on steadily now, but the backlight doesn't come on. The signal is still there (as seen by shining a bright flashlight on the screen and looking closely). Brightness is at 100%, so it's not that. I tried to read the voltages at those four headers I had questions about (guessing that they may be backlight power?) and they seemed to be in the .25-.36 mV range. Since I have no idea what they are or what voltage they should be, that's pretty useless information, I guess. FWIW, I do still read continuity across the fuse, so that isn't blown.

I'll poke around a bit for what to do regarding dead backlights, but I don't know how much further I can chase this thing. Let me know how yours turns out.

 
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donald,
No caps yet, probably tomorrow. Those connectors are to the backlight. Don't know what to do next. I'll keep in touch.
Tom

 
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Thanks for the schematic, Tom.

No luck though. I think that replacing the caps was good progress, as now the power button light stays lit solidly, but the backlight still is not coming up; which I think is a separate problem. It looks like the IP board is functioning properly as it has the correct voltages going to the main board and some voltage going to the lamps.

I really tore into it today, taking apart pretty much everything there is to take apart. I got the bulbs off and they're kind of dark at one end like regular fluorescent bulbs are when they go bad and they don't light up with voltage applied to them. This thing's been through a lot between my experiments and the power situation, so it's hard to tell why they are bad.

I think that the monitor thinks it's working though after the capacitor replacement since the power button light stays lit steadily and there is a picture on the screen (as seen under bright light), but the backlight bulbs just aren't coming on. Hopefully the cap switchout works for you. Keep us posted.

Maybe I'll try THIS cool trick I found online. :D

 
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Don.
sounds encouraging to my situation. We both need to keep in mind the price of repair vs. a new monitor! Good luck, keep in touch. BTW did you get the e-mail?
Tom

 
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Yeah, I got it; thanks again. With regard to the price of repair vs replacement, that's what I was thinking. It's a work monitor and I don't think that we can afford to have me spend many (if any) more hours messing around with it. I'm fairly confident that new bulbs would bring it back to life, but with them costing $10-20 for the bulbs (and there are four of them), the time it would take to put them in, the parts and labor cost of replacing the caps and the time I've already spent poking around it I'm not sure it makes a lot of sense to keep going with it.

If it were my personal display (and it may soon be :icon_wink:), I'd probably keep plugging away at it just for something to do. It's been pretty neat tearing into it and seeing how it works though.

 
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Don,
I picked up the caps this morning and installed them. IT WORKS!!!!. I want to thank you for your help, and wish you luck with yours. Did you get my e-mail with the attachment? If not e-mail me again and I'll try again.
Tom

 
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Don,
I picked up the caps this morning and installed them. IT WORKS!!!!. I want to thank you for your help, and wish you luck with yours. Did you get my e-mail with the attachment? If not e-mail me again and I'll try again.
Tom

Great news, Tom! Glad you got it squared away. Yes, I got your email and attachment. Thanks again for that. I think I'm giving up on mine, at least for now, since I think it needs new CCFL bulbs for the backlight. I'll stick it on a shelf until someone starts asking questions, then we can let the ones who write the checks see if they want to sink any more time/money into it.

Until then, since the capacitor swap seems to have worked and I now have a different problem, I'm going to go ahead and mark this thread as solved.

Question Answered as of 4 Years Ago by Tomcook
 
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I know what you mean, sounds like a plan.

 
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Hello, guys! Please let me enter this discussion. I live in Brazil, so, forgive me for the rough English! Right now I am facing the same problem. I have just disassembled a Samsung 761BF monitor, whose power blue light only blinks but no image is shown on screen. The power supply shows the same blown caps, which differs only in the value for C113 (in my case, 820uF, the same as for C112 and C316). Also blown are C109 and C110, both 1000uF x 10V. I am going to replace all of them and tell later what I have found! If you have any news from this issue, please let me know! Thanks and best regards! Max.

 
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Hi, Max. No news from me; my monitor is still sitting on a bench collecting dust even after replacing the three capacitors. I wonder if something else might have gotten toasted when I tried hooking up my home-brew capacitors. I can, however, still see images in the LCD when shining a light on it or manually backlighting the screen, but the built-in backlight does not work at all.

Hope to hear some favorable results from you and Good Luck!

 
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I used extreme restraint and waited until I had the right components and I am still using the monitor. good luck!

 
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Hello, my friends! Well, I've done some dirty work here: I associated some capacitors to reach the necessary capacitance and voltage. From junk motherboards I got some 1500uF 16V caps and put in series to achieve the 25V and 820uF specs. Also two 470uF 25V in parallel did the job in place of one of them. For the 1000uF 10V caps I used two 1500 uF 16V standing alone. And it worked fine, as their goal was just filtering (some of them are put in parallel in the circuit!). I thank you for the valuable information. 'Till next time!

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