Question about NEC MultiSync LCD1830 18.1" LCD Monitor

4 Answers

Backlight does not light

After we drove this monitor 100 miles, it no longer has a working light. how can I determine if the fault lies with the inverter or with the bulb itself? would you please email me your answer at roger@rogergrafstein.com. I asked a question earlier and something came back in a file format that my PC can't handle. thanks in advance, roger

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  • RGrafstein Dec 27, 2007

    Thanks for your interest and prompt reply. I have already turned it on and off several times. I don't understand what you mean by "make sure it gets enough power. The monitor worked until it was transported 100 miles to a new location and now the screen is black but using a flashlight I have determined that its getting the signal from my PC.
    Seems to me that its most likely a failed inverter or failed bulb. do you agree? how can I test for which one of these parts is at fault?
    Now that I have the whole thing taken apart, I want to be able to inspect the bulb in order to rule-out or rule-in that part. I think I could check the continuity in the bulb if I find it and if the filament appears intact.
    If the bulb tests out OK, I would think its the inverter that's at fault.

    Thanks in advance for your reply, Roger

  • RGrafstein Dec 27, 2007

    As stated in my earlier posts, this NEC monitor has a black screen, even though the green light is on and I can see my PC desktop image in the monitor by using a flashlight. I read on line that the inverter often fails on these. I have disassembled that monitor to the point where I could replace the inverter ($70), BUT what if its just a problem of a burnt-out backlight bulb? How do I find that bulb in order to inspect it and check continuity? (I currently have all the printed circuit boards exposed, but I haven't tried to get any further into the innards without good guidance.
    Thanks in advance for you help, Roger

  • RGrafstein Dec 27, 2007

    So far two different "experts" have provided me with absolutely no help at all! I need an expert who can follow my train of thought, which I have layed out in detail in my previous posts. And I need an expert who is really familiar with LCD monitors, like those made by NEC. Please help,
    Roger

  • RGrafstein Dec 27, 2007

    Skippy, I'm home again and I could work with you anytime in the next hour and a half (to 11:30 PST) if it would be convenient for you. If not, could we do it any time after 10 hours from now (8 a.m. PST).
    I tried a suggestion from the previous expert to check for inverter's high voltage output and there seems to be none at all. so I guess its either a fuse, like you suggested or some problem in the powersupply to the inverter. I looked over the printed circuit boards for a loose wire or plug and found none.
    I'll try to add an image - monitor innards - to this posting.
    thanks,
    roger

  • RGrafstein Dec 27, 2007




    here it is.

  • RGrafstein Dec 27, 2007

    Thanks for you continued interest. I see white and pink wire, But there is a pair of these at Each of the two ends of this board (is this the inverter?). Also each pink wire has a black wire with it (smaller size than the pink wire) and each white wire has a smaller white wire running side-by-side with it. I am assuming that each set of pink/black/whhite/white wires goes to a different bulb.
    I think I see the transformers that you refer to: there is one near each end and they are the biggest components on the board (they are each numbered 0053 1711S). Have I got it right so far?
    Now, I don't recognize any other transformers and I don't see anythings that look like yellow or orange fuses. Please send me more detailed instructions on how to find them.

  • RGrafstein Dec 27, 2007

    let me know if it would help for me to send a more detailed photo of one end of the inverter.

  • RGrafstein Dec 27, 2007

    I found on fuse marked F1 right next to a little (1/4 " tall) can marked *1UY 330 16V. (the * stands for a tiny box at the beginning of the part number.) Resistance measures 0.0!
    Is there a second F1 fuse that I need to find and check? I can't seem to find it.

  • RGrafstein Dec 27, 2007

    I didn't mention this before, but maybe it will be helpful. I found that the inverter IS getting power from the main board. there are 7 terminals where 6 blue wires and one white connect to the middle of the inverter. I touched a few of them with my voltmeter and read 12v in some cases and something less than that in other cases. Let me know if you want me to do more measuring there.

    (by the way, when I tried to find a high voltage output from the inverter, I used the contact points on the inboard sides of the two ivory colored connectors at each end.

  • RGrafstein Dec 27, 2007

    I'm sorry to be so dense or blind. Still can't find it. I have to leave now for dentist appt. When I return, I will post a photo that shows the "other side" of the board in detail. thanks for your patience, Roger

  • RGrafstein Dec 28, 2007


    1. I found an F1 in the upper right, but I can't find the second F1. Can you point it out to me please? Thanks, Roger

  • RGrafstein Dec 28, 2007

    here's the middle board

  • RGrafstein Dec 28, 2007


    1. here's 3rd board

  • RGrafstein Dec 28, 2007

    Skippy101 I'm counting on you to guide me to a solution to my problem! Please don 't let me down!

    I believe the log of some previous monitor problem troubleshooting that you just posted is useless to me.

    What I need from you at this point, in order to follow through with your promising ideas earlier today:
    1) Are you certain that my inverter has a 2nd fuse labeled F1?
    2) If so, exactly where is it? (could it be mis-labeled on my board?)
    2.5) If not, what do I do next?
    3) If I do find the other F1 and it's resistance is greater than zero, what would the solution be?
    4) If its resistance does = zero, what would I do next?
    5) why did you ask me to post photos of the other two boards?

    We both have put in a lot of time on this. Hours. Will you stick with me and see this thing through?

    Roger

    p.s. if you need me to measure any voltages or resistances, just tell me where.

  • RGrafstein Dec 28, 2007

    If we can be SURE that the entire problem is located on the inverter board, then I would spend the $70 for a new one and just replace the one thats there. If I was retired, I might want to get a tiny soldering iron and multimeter w/ diode checker; but I'm not retired yet. Actually, my son is paying me to fix his monitor and he doesn't want to spend much over $100.
    Also, I don't see any "brown" or "burnt" areas on the inverter board.
    So, are you sure its an inverter board problem? Why do you think so? are there any other simple tests we can do to confirm that and also that the bulbs are OK and that the other two boards are working well?
    I very much appreciate your time. I'm going to bed now, but look forward to seeing your reply in the morning. Good night, Roger

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4 Answers

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Hi,

If I may add:
1. Your PC & display are both OK;
2. You need to determine which is at fault, the CCFLamp or the Inverter:
2.1 If the inverter is working, you would be able to read a high frequency high voltage at the terminal connector that goes to the lamp, if yes then it is the lamp (use a DVM set to AC 1K);
2.2 If no, then you need to check if the inverter is getting +12. If yes, inverter is defective, if no then power supply is in question.

Offhand, I would suspect simply a loose connection somewhere (considering that it was transported. Wiggle all connectors to make sure they are snug and tight.). The next suspect would be the lamp. They have a tendency to burn their ends/connectors or develop corrosion over time which would manifest when jarred.

Hope that this be of additional help/idea. Pls post back how things turned out or should you need additional information.

Good luck and kind regards.

Posted on Dec 27, 2007

  • Louie  Role
    Louie Role Dec 27, 2007

    Hi again,

    A friendly reminder pls., the inverter's output as said is high freq/high v, it has a tendency to arc across terminals or test prod. Please exercise extreme care. It is almost like a miniaturized FBT of a CRT monitor.

    Cheers.

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  • 143 Answers

Sorry you are having this trouble these lcd monitors when you can still see your desck top but no light comes on then you might have blown a fuse inside the monitor the inverter is fine you have problems in the dc to ac converter in the monitor it self . how long have you had this monitor. you can take it apart and check for your self it is very easy all lcds no mater how big or small have a ac-dc converter in them small serface mount fuses that look like resistors go out also bad connections . when you take it apart you will see that the lamps are built in to the screen it is more costly to replace the lamps than to replace the monitor. get back to me and ill give you step by step to find the fusess. good luck

Posted on Dec 27, 2007

  • 6 more comments 
  • marco amezcua
    marco amezcua Dec 27, 2007

    ok on theboard that is to the most left if you are looking at your screen you will see were the lamps connect to the board it should be a pink and white wire andthere will be 4 sets next to them you will see on each side two trans formers small ones next to them you will see on each side one small orange looking or yellowish looking resistor this is a fuse messure it with a dvm or digital volt meter in ohms it should read 0 ohms if anything else it is bad replace it it should be like 1.5amp or 2amp fusse this will fix your problem

  • marco amezcua
    marco amezcua Dec 27, 2007

    the fusses im talking about should be labled f1right next to the trans formers

  • marco amezcua
    marco amezcua Dec 27, 2007

    you will havanother fuse on the other side looks just like the first one you checked

  • marco amezcua
    marco amezcua Dec 28, 2007

    that is a great pic can you post all three boards like that make sure they are complete k thanks

  • marco amezcua
    marco amezcua Dec 28, 2007


    Symptom: Backlight flashes short after start and then shut down.
    I've invested several hours:
    power board
    - checked out power supply capacitors
    - fuse 25V / 2.5A
    inverterboard
    - replaced C11 and C12 = 180nF / 250V
    - check fuse F1

    When the monitor was warm > 25° - it works
    Next day - dark screen.

    replaced the whole inverter board --> the same
    Then I found your schematic:
    CN1 / 7: 250 Hz square 8Vss = duty cycle for brightness

    The protection circuit causes shut down the backlight.

    Each lamp connector CN2 – CN5 has a feedback with a rectifier. The DC voltage is measured above C13, C22, C24 and C25 and should be about 5V.
    The comparator U1C and U1D compare this voltage against 1.55V (Pin 8,10 – C16).

    The feedback of CN5.2 ( C25) had only 1V in cold condition. So the backlight shut down.
    Next try only with power OFF / ON.
    I change the connector CN5 and CN4 and also CN2 an CN3 – oh, oh – this fault moves to C24.
    Okay, the backlight has a little problem. This is okay, because it has plenty of hours on duty every working day the last five years.

    Change R28 from 680Ohm to 1kOhm, and increase C16 from 1µF to 220µF

    Now the backlight turns on for 10sec. ignoring the protection circuit.
    Backlight warm up and turns to normal operation.

    Attention: This modification is no general repairing method for the dark backlight.
    You’ve carefully checkout the behaviour with an oscilloscope before your change the components. Check the power consumption on the 12V CN1 / 1 (1.2A @brightness=50%; 2.2A @ brightness= 100%).
    In case of disabling the protection circuit even for 10 seconds you might destroy the power circuit or the high voltage inverter.
    This case: more or less weakness of the backlight bulb.

  • marco amezcua
    marco amezcua Dec 28, 2007

    i found that at one of my sister sites good luck

  • marco amezcua
    marco amezcua Dec 28, 2007

    yes i will help you ok looks like there is only one fuse hummm ok on that long board that the bulbs plug into you will see that the board gets discolored like a brown this is were most of the heat is generated do you have good soldering skills here we go solder all the conections around that look brown next we are going to check some transistors do you have a volt meter that has diode checker you will need this ok when you are ready let me know k

  • marco amezcua
    marco amezcua Dec 29, 2007

    ok so i did more research on this and found that on this model if the fuse is still goog remove the skinny board flip it around and solder any connections that might look bad loose or that might have gotten hot check all transistors with a dvm and solder them as well if you find one that might be shorted from emitter to collector or to base then replace this will be time consumming for beginers you might wat to replace the board yes this is your problemthe little board or inverter sorry i didnt get back to you sooner just want this to be right foryou good luck my freind and feel free to call on me any time

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  • Master
  • 790 Answers

Hey

Your guess is right its the back light bulb which has gone wrong ... And as i know warranty covers for the back light too which u can get replaced free of cost ...

Posted on Dec 27, 2007

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  • 209 Answers

I'm not sure but maybe try ..turning it on and off a couple times, make sure it gets enough power.

Did the monitor work before ?
are you hooking it up to your pc or as a tv ?

Posted on Dec 27, 2007

  • 1 more comment 
  • Simon Zwaan
    Simon Zwaan Dec 27, 2007

    I thought the problem may lie in how many other devices are plugged in the same outlet.



    It sounds like you know your way around Tv's. so yes, i would recommend seeing if the filament in the bulb is still intact, since this would be easier[make sure you unplug it though :p]

  • Simon Zwaan
    Simon Zwaan Dec 27, 2007

    Can you see the bulb ? and see if its intact still ?

    maybe you can test it somehow...but dont turn the tv on with some parts removed, that will most likely burn some fuses.

  • Simon Zwaan
    Simon Zwaan Dec 27, 2007

    I would say contact support and get them to repair it, they should do it for free if its under warranty.

    and if you complain enough they might do it cheap to keep their good name.



    That's all I got, sorry

    hope it helped.

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