Power Supply from LCD Monitor help

Discussion in 'General Electronics Chat' started by nickmind, Oct 12, 2010.

  1. nickmind

    Thread Starter New Member

    Oct 12, 2010
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    Hello all,

    Last month, my “just under 2 year old” HP 22" w2207h monitor started blacking out, meaning the picture would disappear for a few seconds. Then it started getting worst, as the picture would go out for minutes, after just being power on for a few minutes. So I was about to junk it, after HP telling me there is nothing they can do. But I started to search on repairing it myself, after looking at testing capacitors, and other things. I open the bad boy up.

    That’s why I’m posting. I getting reading that have me questioning if I’m doing something wrong or my multimeter is off. I’m using a Fluke 79 III RMS multimeter and have it set to capacitance.

    I started with the power supply, thinking that is most likely to be the problem. All the caps on the SP look normal. So I started floating leads and testing away. On the first cap, its 680 uF 25V, after floating and discharging the leads I’m getting ~650 to 655 uF on the meter. The on a second cap, it’s a 470 uF 25V, and on the meter I’m getting ~450 uF. Either I’m good at picking caps or something is off. So I start testing more, the third cap, is a 470 uF 16V, im getting 445 to 450 uF. Then a fourth and firth, all caps I tested on the SP are below their rate. Is this normal? Are these caps good? Or is that normal that all the caps are reporting under their rate and need to be replaced? I did test the multimeter on a 100 uF cap from something else, and got 108 to 110 reading.

    Am I doing something wrong?
    Attached a pic of the SP? Were should I start testing? Thanks for your time and help,

    Nick
     
  2. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Hi Nick, Is the powersupply faulty? you have chacked the voltages coming out of it? For checking SMPS capacitors i have found checking there ESR ( series resis) with a ESR meter more acurate than using a capacitance test. Have Pic of A kit I built of an ESR meter u can use to check capacitors in circuit (Power Off) This i have found invaluable. Daryl
     
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Frrst thing to do is look very closely at the circuit board for suspicious solder connection, especially around any component that carries power.
     
  4. nickmind

    Thread Starter New Member

    Oct 12, 2010
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    I have been reading that ESR meters are more accurate then testing the capacitance using a multimeter, but the question is, since i don't have a ESR at the moment, can i test these caps using this current method? And if i can, what are these reads telling me? Are the good or are the bad? Or is something else wrong.

    Trust me i did, fine tooth comb. Nothing jump out at me as bad. Tho, im a network engineer, with every little experience with this.

    I do thank you guys for your replies.
    Nick
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    The tolerances of electrolytic capacitors are often specified as -20%/+80% so their value can be 20% lower than specified or 80% more even when new.

    Does your capacitors testing result meet this criteria?
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,750
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    See the caps top for bulging, even for the slightest bulge will create problem.

    See the big one too.

    If no bulges, I doubt that they are the problem.

    U need to go for voltage measurements, Are up to this task?
     
  7. nickmind

    Thread Starter New Member

    Oct 12, 2010
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    I think so, how do I run this measurement? Give I have a 680 μF 25V cap, how do i run the test and what reading should i get?


    THANKS ALL, for your help and support.
    Nick
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Measurements means tht u connect the Monitor and Measure DC voltage.
    For this job I will need lot's of pictures to guide u. that is why I asked u if u are up to it.
     
  9. nickmind

    Thread Starter New Member

    Oct 12, 2010
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    Sure, I can take pics, if you have the time. I don't want to put you out.

    Thanks,
    Nick
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Ahh, wait a minute - see all those little triangles over on the right side with "DANGER!" next to them? That means high voltage.

    Those black rectangles towards the right are HV transformers to fire the CCFL backlight tube (CCFL = Cold Cathode Fluorescent). The starting voltage for CCFL's can easily exceed 1KV during start-up, and once the tubes light, the typical operating voltage range is between 300v-600v.

    These are dangerous voltage levels, and you don't want to be working near there unless you know what you are doing, and have proper test equipment and a proper work environment.
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    God !! I love u Sgt. U sure do remember to warn us abt the dangers involving HV :p

    I was about to get to tht part. but as usaul u have beaten me again. :)

    To OP..
    Now the warning and thread locking part is dealt with, are ready to tackle the trouble shooting.
    U will need a DMM, Temperature controlled Iron, 60/40 or eutectic solder, a sucker or braids. a Camera , A PC to Log in to AAC ;) and patience plus u must have the courage to hold ur self from making any changes or tests or checking parts from ideas tht wiz thru tht had of ur's from time to time during this journey.

    Acknowledge. :D

    {ed}
    Update ur profile, add location and GMT timing will help
     
  12. nickmind

    Thread Starter New Member

    Oct 12, 2010
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    I hope DMM is Digital MultiMeter? If so, I'm good to go. I got a fluke, Iron up to 800 with solder and braids, kick ass cam and ... Ahhh, i need a PC to get on AAC... :) Lets blow some **** up. LOL

    Nick
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,750
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    OK then..assemble the monitor completely as it was before. But without the back cover.

    Get a good closeup of the boards/ back layout. I like to see what I am repairing.

    From these pics I will guide u to fix ur monitor. Just follow my lead and I promise u tht this will teach u a lot.
    Pictures need be well lit and high resolution so I can zoom in to see the details.

    I don't need to tell u the HV involved and how fragile a LCD panel can be since u already have dismantled it. So I will skip these.
    But keep the monitor face down on a towel or something, this prevents un-intentional scratches.
    U will be plugging & unplugging the cables a lot, so always try to do this gently.

    Never apply power unless I say so. Period
    Read and double read the post.

    Now I assume u have the monitor assembled. Give power, observe the screen and power led as u switch on.
    Post every single detail u see and hear.

    Please update ur profile and ur working time.
     
  14. nickmind

    Thread Starter New Member

    Oct 12, 2010
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    I'm uploading full res pics to photobucket at the moment, I will send a link once it is complete.

    But I have a bit of a problem with putting the monitor back together. If I do, i have to use the case, which will hide both boards. Between the lcd panel and the case.

    But I can explain exactly what happens. When I press the monitor's power button, both the led light for the power button, and the monitor will turn on. A few secs later the picture will show, when cold, it will remain this way (working monitor) for about 1 to 8 minutes. After that, the monitor blacks out for a few secs (like the monitor lost video sig) then the picture will show again, then blacks out again. It will do this for hand full of times, then remain black. During this whole time the power button's led remains lit. During the black out times, not even the OSD will display. Meaning if I was setting some settings on the OSD, and the monitor blacks out, everything goes black. No sounds that i can hear.

    That is why I think its the PS.

    Other then that, lets do this thing and I would like to thank you for guiding me. I'm in the US on the west coast, but im up 20 hrs a day.
     
  15. nickmind

    Thread Starter New Member

    Oct 12, 2010
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  16. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U are exactly 12Hrs different from me.

    Ur problem seems to be a CCFL related fault.

    Let me check the picks.

    Update me with what u have done so far
     
  17. nickmind

    Thread Starter New Member

    Oct 12, 2010
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    Took out some caps to see if they were good using a DMM, but all readings are showing 20-30 μF lower then their rates, but all of the caps show this same reading.

    That is it, i was wondering if i was doing something wrong.

    Do you mean the Panel is fault?
     
  18. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    From all of the pics, only 1 is close to my likin :D.
    Don't worry you'll get there.

    I see this is quite a big one, and In order to trouble shoot the boards need to be connected. Since the back shield is used to mount the boards, things are going to be a bit difficult to do the testing, U might need a buddy on this to help u..

    [​IMG]

    See the PIC.
    1,2 & 3 are the parts tht we will be working with.
    Part 4 is the back cover / shield, which will be left out

    Connect the boards to the LCD accordingly in such a way tht solder side is facing up. Put a hard cover book or any Insulating material in between the boards and the LCD.
    This is to prevent the heat sinks from touching the back metal plate of the LCD.
    See tht the two boards are completely isolated from the LCD back.
    U can swap the CCFL cable, it does not matter which one goes to which.
    CCFL are the two lamp connectors ( white, Pink) protruding from the corners of the LCD. It's OK to swap these connectors as they are the same identical lamps inside. But keep in mind tht the jack is firmly seated in to the CCFL connector. If they are loose. U will see sparks from those PCB connectors and is not good for the board.

    Interconnect the two boards and the LVDS cable too. Connect the power code, But do not power up yet.

    But before all these I want you to take Pictures of the two boards. exactly from top, not side ways. Both the component and solder side.
    Avoid flash glare and get good closeup single shot. I do not need multiple shots. 1 complete Good shot of each from top is all I need.

    Now after the connection is set up. Snap a PIC and show me.
    Then I can tell u the measurement points and the works
     
    Last edited: Oct 14, 2010
  19. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,750
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    The caps reading are way off too much. U are doing something wrong

    U said All readings, which tells me u are mistaken. All the caps will never go bad

    If U can see a good picture than the panel is AA OK, CCFL related means, Lamp OR inverter fault
     
    Last edited: Oct 14, 2010
  20. nickmind

    Thread Starter New Member

    Oct 12, 2010
    11
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    How are these?
    http://s206.photobucket.com/albums/bb282/nickmind/HP 22 monitor w2207h/Take two/

    I am uploading videos of how I test the caps, the first is DMM settings. The second is the testing, bad video with zero editing. I got to get to bed soon.

    Tomorrow morning, i will solder back on the caps, then connect the monitor back up, then take some pics to show you how i connected them.

    Thanks again for your help
     
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