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Dell 2408WFPb - What to replace?

Discussion in 'Troubleshooting and Repair' started by jeffshead, Jul 4, 2019.

  1. jeffshead

    jeffshead

    7
    1
    Jul 4, 2019
    I have a Dell 2408WFPb that is giving me the issue depicted in the images below:

    [​IMG]
    [​IMG]
    [​IMG]

    Sometimes the screen is completely blank when I power it on. I get only that thin, blue dotted line at the top of the screen (as depicted in the second image) when I use the input option button to cycle through the inputs.
    The monitor functioned properly, a couple of times, when I unplugged the power cord and held the power button in for 10 seconds, released the power button and then reattached the power cord.

    I love this monitor and would like to repair it but my soldering equipment and soldering skills stink!

    Is it possible to tell which component (i.e., power supply, main PCB) is causing this issue instead of just throwing parts at it?

    This happened after a power outage. What really ticks me off is the fact that the monitor was plugged into a fairly expensive UPS with sine wave output. The monitor was fine when the power went out and it was running on battery. The issue occurred when the power was restored. I don't know what the freakin UPS did to cause this.
     
    Last edited: Jul 4, 2019
  2. davenn

    davenn Moderator

    13,212
    1,730
    Sep 5, 2009

    As in, you tried the monitor on another PC ??

    That bottom pic ... what are the words in the blue part ? ( your pics were not up close enuf to read)

    If monitor works OK on another PC, then try a different video card in the PC
    if that doesn't work, then it's something deeper and most likely wont be fixed

    Have you checked the power rails from the PC power supply ?
    + and -12V and 5V, maybe a 3.3V rail as well
     
  3. jeffshead

    jeffshead

    7
    1
    Jul 4, 2019
    Thanks for responding!

    All three pics in the original post are simply showing you the same box that slowly glides across the screen when nothing is connected to whichever of the monitor's inputs (e.g.,VGA, DVI, HDMI) that is indicated within that blue box. The third image is what it should look like.

    This is a monitor issue so it does not matter what PC it is connected to or which input is used. The issue is the same with a PC connected or disconnected regardless of the input used. When connected to a PC, whatever is on the screen is just as screwed up as what's depicted in the first two images in my original post.
     
    Last edited: Jul 4, 2019
  4. 73's de Edd

    73's de Edd

    2,613
    1,065
    Aug 21, 2015
    No DVI #1 cable. . . . . . . . . .input.. . . . .is what is read.
     
  5. jeffshead

    jeffshead

    7
    1
    Jul 4, 2019
    For clarification, please read Post #3 :) I know there is nothing connected to DVI input #1. That is not the problem.
     
    Last edited: Jul 4, 2019
  6. 73's de Edd

    73's de Edd

    2,613
    1,065
    Aug 21, 2015
    Sir jeffhead . . . .

    I was merely commenting that " No DVI #1 Cable " was what I was reading as per Dave's comment that he could NOT read it.

    Now I realize that with no input that you are only going to get that simple small logo on the screen and possibly after a length of time it reverts to a time shifting into a floating across the screen, mode . . .a . . la. . . .screensaver.
    Soooooooooooo . . . . . if I look at just the DVI connector as you show, I see it being distorted and with MULTI distorted jagged abberations imparted into that logo, instead of the normally clear and distinct logo. Sort of an UBER_UBER DISTORTED X 10 . . . moire pattern as you experienced in your photo . . .with electronic video frequencies intermixing.

    Now what I am submitting for techno referencing, is being a like situation, with your same unit, but with this person having a FULL normal HOME screen size, with its logos being shown.
    BUT what I do now equally seem to see, is the WHOLE screen is being full of minor small abberations, such as it seems as is occurring to your very small logo of a DVI connector.

    He keeps plugging and pausing and unplugging the unit into the AC outlet and finally he gets lucky in the respect that he gets a good, steady undistorted normal display.

    In one of the bottom comments , one of the more technically learned audience, is suspicious of a deteriorated / ineffective filter capacitor in the systems power supply. The innefectiveness of degree of filtering is imparting a modulation upon the video display . . . . creating the harsh video abberrations..

    I would think of the same situation in your case . . . . . .try it and see if that is your like situation.
    If you happen to luck out, then we see what info is floating about on a like DELL power supply schematic.

    HOWEVER . . . . .Don't overlook the possibility of the same effect being introduced by your UPS unit, if you haven't already done so.
    So initiall . . . . . .y try the Dell with it being plugged into the normal AC OUTLET for a test.

    What say ye ?



    73's de Edd . . . .

    If at first you don't succeed, go back and destroy all evidence that you even tried !
     
    Last edited: Jul 5, 2019
    davenn likes this.
  7. jeffshead

    jeffshead

    7
    1
    Jul 4, 2019
    Thanks!

    I already tried different outlets on different circuits; same results.
    Yes, if I remove and replace the power cord several times, I do sometimes get lucky and the monitor works until the power source is disconnected again.

    So it would seem I have the same issue as demonstrated in that video. How can I be sure a cap is the culprit and how will I know which one(s) to replace?
     
  8. 73's de Edd

    73's de Edd

    2,613
    1,065
    Aug 21, 2015
    Sir jeffshead . . . .

    Ohhhhhhhh-Tayyyyyyyy . . . . . . now take a look at your first photo submitted and my illustrations frame, and see if you don't think that they might have had the same mama ?

    Now, as for that references power supply photo content . . . despite its focus and dimensional parallax shortcomings.
    If you take apart your monitors clamshell case *** and its snap together fastening you shoud be able to compare my reference to that units power board.
    Major points of comparison will be the top left corners string of E-caps and the larger heat sink, located just below them. Then the YELLOW kaptan tape surrounded, MAIN switch mode power transformer.
    Then drop down to a minor heat sink.
    Pass across the board to past center for the MAIN line derived DC power for the system, coming from the side mounted large black E-cap.
    To its right, taking on an upside down L route, is being all of the lined up ancillary components associated with AC line power processing.
    That ends up with the back of the IEC line connector at bottom right corner..
    Last significant item, is being the units smaller STANDBY power transformer in its YELLOW wrapping.
    If this is being your units power supply, then we have three options.

    ZF7TbmG.jpg


    Come back to me . . . . .

    *** It snaps together . . ." REEEEEEEAL " easy. . . . but your initially getting / peeling it apart, is difficult! . . . BECAUSE . . . . it is always wanting to snap back TOGETHER, within an instant.
    Inserting in and and taping down round toothpicks as you progress with opening an initial section , by using an inserted . . . . mar avoiding . . . hard polypropylene orange peeler tool /or/ plastic spatula.

    If you have thin bamboo skewers, they work even better than toothpicks in having them stay in place, with their long length.
    Once you get > 50% of the back spread apart . . . . wheeeeeeeeeee . . . you're home free !

    TECHNO ILLUSTRATION . . . . . of suspect DELL unit being utilized


    73's de Edd . . . . .



    TWO BLONDES GO FLYING!

    Two blonde pilots are trying to land an airplane.
    They start descending and as they touch the ground the one blonde screams
    to the other blonde, "Bambi, pull up, the runaway is ending!"
    She swiftly gets the plane back up in the air.
    They make a big turn and start descending again.
    The moment they touch the ground, the first blonde screams again, "Get the
    plane up, Bambi, the runaway is ending!"
    The second blonde swiftly gets the plane back up in the air. They make a
    big turn and start descending again. This goes on again and again...
    During their fourth descent the second pilot says,
    "This is so dumb, Candi, they build this huge and expensive airport but with
    it having such a short runaway."

    "I know," answers Candi, "But look how W I I I I DE they made it!"
     
    Last edited by a moderator: Jul 13, 2019
  9. jeffshead

    jeffshead

    7
    1
    Jul 4, 2019
    Here is what I have:
    [​IMG]

    I didn't see any bulging or leaking caps.
     
  10. jeffshead

    jeffshead

    7
    1
    Jul 4, 2019
    Just to be clear, the panel is not completely blank, the power button always works & turns green & stays on when pushed so it doesn't appear to be the same issue that so many others have reported on different forums.

    I did check voltage on the connectors coming from the power supply that are going to the inverter and main logic boards. I do get 23.xVdc. The voltage of the big capacitor on the power supply is 165Vdc in stand-by mode and 293Vdc in operating mode. Those voltage readings of that big capacitor are the same when the monitor is functioning properly and when the problem occurs.
     
    Last edited: Jul 5, 2019
  11. 73's de Edd

    73's de Edd

    2,613
    1,065
    Aug 21, 2015
    Sir jeffshead . . . . .

    Well now . . .aren't you one well motivated, electro-mechanically inclined, actual DOER with the unit now being fully exposed and ready for analysis.

    Seems like the initial suspicioned board, as being compared to this used boards layout, has its parts being altered around in their placement.
    With your separate little AC line input board , having all of its fusing and Electro Magnetic Interference - Radio Frequency Interference - Additional Crap type of supression circuitry, all lined up vertically at the left side and running up and outputting at the RED WHITE wired 2 pin connector as its top connection.
    This initial board has a two way operation, in its supression of the unwanted coming in from the AC line and keeping any internally generated interference from getting fed back into the AC line.

    I have the newer pic of the actual board initially marked up in case later referencing to parts need to be made to it.
    I can imagine that the larger right side of the board power transformer [ K ] is creating a HEFTY 24 volt supply with the power diodes mounted on [ M ] and the cluster of all shunting [ N ] E-capacitors and then their output routes up to the boards top LEFT corners 12 or so pins connector that feeds the LCD backlight driver board hidden behind the left sides metal shield.
    Sooooooooo . . . I really don't see there being enough E-caps on the actual PS board to account for all of the units sub supplies involved .
    So I rea l l l l l y think that those supplies origins on this board are being routed down via the boards top RIGHT hand corner connector and down to the main pcb.
    There you see an inset that I have placed on the end of the photo reference; where you see at least 4 supplies [ O ] toroidal filter inductors and associated E- capacitor clusters being around them. I am seeing 2 major E-caps 10 minor ones and 2- 4 smaller sub ones.

    ALSO . . . . being covered in my photo in the mid inset . . . . I can now additionally see that on the MAIN board are 2 or more possibilities.
    I now point them out physically, as item [ 1 ] appearing to be a linear regulator and it has input and output E-capacitors surrounding it.
    To the right is a complete stand alone switching regulator item [ 2 ] with its RED ringing inductor and associated E-caps surrounding it.

    Check out all of the E-caps cans within all of these mentioned locations and just HOPE that merely one . . . or more might show a degreee of upward doming of its top of can.
    Secondarily let the unit run for multiple hours of run time . . . . . . either bad or good display condition, basically, you're just wanting to warm up the set.
    Do index fingers tests to two tops of caps at a time to see if you find warm ones, failing units run a bit on the warm side, on their temperature. . . . on up to . . . . . " EWWWW ! . . . . .thats hot !
    (Or should you be so blessed as to already own a laser based thermal spot temperature thermometer . . .or can borrow one from someone.)

    You say . . .
    Just to be clear, the panel is not completely blank, the power button always works & turns green & stays on when pushed so it doesn't appear to be the same issue that so many others have reported on different forums.

    Right . . . . . so now our consideration is being the PROBABILITY of the unit displaying that highly abberated type of graphics display.
    And . . TRUE . . . that you did not find that . . . . "HOLE, dead center in the forehead, for certain clue . . . . . like others encounter in their finding of a canned electrolytic cap with its top outwardly domed to the extent that the weakening X crossing depressions in the can have fractured. That then lets developed gas pressure out and detrimentally, starts a decline in letting the decreased internal damp electrolyte totally dry out, from its newly opened exposure to the atmosphere..

    BUT now, what are the chances that if you turn on the unit, from a totally cold start up , that the corrupted display will appear?
    AND if it does appear in its abberated state, is there any chance that after 15-30 minutes of run time, that its thermal effect might cause the screen to instantly " pop " into a good display, on its own ?

    On the other hand, I suspicion that if you initially turn on the unit and it gives a good display, with continuing run time and warm up, that the display would HOLD with a good display, and be totally fault free for 3 - 6 - 9 - 12 hours.

    All in all, I am wondering what are the chances of the display coming on with an abberated graphics condition . . . . so that we can evaluate parts, with it staying in that condition.

    Waiting for those findings and I might need help in your inspecting some parts for their part number ID's.


    PHOTO SNIPPET REFERENCING . . . . .

    [​IMG]

    https://i.postimg.cc/Z4JtFszY/DELL-2408-s-Power-Supply.png



    73's de Edd . . . . .


    FULL NAME . . . . . . what a mother calls her child when she's hopping mad at him / her. . . . . . and, usually its a boy.




     
    Last edited: Jul 9, 2019
  12. jeffshead

    jeffshead

    7
    1
    Jul 4, 2019
    I left the unit on for a few hours in each state and the display never changed from good to bad or vice versa. Unfortunately, I do not own a laser based thermal spot temperature thermometer nor do I know anyone that I could borrow one from. I did not find any warm or hot caps by touch.

    I could no longer deal with the tiny monitor I was using as a temporary replacement so I ordered both a power supply and the main board for the monitor. The main board was the culprit. No issues since I swapped it out. No visible damage on the top or bottom of the bad board. I checked the voltages with the new board installed and everything is the same as with the old board. Even the voltage on that large cap on the power supply. It does not go above 293Vdc in operating mode.

    Thanks so much for helping me. Much a appreciated! I don't know what is wrong with the bad board. I wish I did because I would like to fix it and keep it as a spare. I do not own an ESR meter so I guess I'm out of luck.
     
    Last edited: Jul 12, 2019
    davenn likes this.
  13. caps

    caps

    155
    8
    Jul 29, 2018
    This is not necessary. Maybe the ESR will increase, very little. But this is enough to create problems.
    A lot of trouble is caused by leakage of capacitors. You can check with an analog multimeter. But in many cases, the leakage manifests itself at an operating voltage.
    You can independently make a very simple scheme for checking capacitors for leakage or buy a ready-made device. This will be useful to you in further work.
     
  14. caps

    caps

    155
    8
    Jul 29, 2018
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