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Need Schematic for Dell/Sony P991 19" CRT Monitor

Discussion in 'Electronic Repair' started by Bob Shuman, Jan 16, 2006.

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  1. Bob Shuman

    Bob Shuman Guest

    My 4-year old 19" Dell (Sony) monitor is having some HV problems. Yesterday
    my 12-year old daughter said it "popped" a couple times and the screen
    flashed/changed size along with the pop and then returned to normal. She
    came to get me immediately and when I got there it seemed to be fine for
    about 5 minutes, then popped once and lost the image completely. I turned
    off the monitor right away at the switch, waited a few minutes, then tried
    to power it back up. It turned on, lost the picture within a fraction of a
    second, and began emitting a new barely audible sound. This sounded to me
    like a high voltage discharge so I disconnected the unit from the computer
    and carried it down to my bench for further analysis.

    I opened up the monitor case, removed the right (looking from the rear)
    metal HV shield and then plugged in and turned on the monitor without a
    video input signal under a low light situation to see if I could identify a
    flash/spark that was accompanying the sound. This proved to be very easy
    since it was a glass discharge protector located at designation SG901. (It
    lit up pretty much like a neon bulb...) I kept it powered up just long
    enough to verify that none of the other protectors on the CRT socket board
    were lit and that the sound was coming from only the one device. I saw no
    obvious arcing or shorts anywhere. My assumption here is that the HV output
    has drifted high and the discharge is the protection which was designed to
    kick in working as expected.

    I have removed the main board, but do not have a schematic. I'd like to
    start with the assumption that the protector is working as designed and
    check the values of the critical components in this circuit against their
    specified values. Unfortunately, I do not have a schematic to identify
    which ones they would be. I'm hoping that someone can send me the schematic
    and/or their recommendation on fixing the problem.

    Prior to encountering this issue, the monitor had worked flawlessly and I
    would prefer not to have to purchase a replacement. Thanks in advance for
    your assistance and thoughts.

  2. kip

    kip Guest

    First try cleaning the spark gap..
    Second disconnect the base assembly an see if it arcs whilst disconnected
  3. Bob Shuman

    Bob Shuman Guest


    Thanks for the reply. The device that is sparking is a sealed glass bulb.
    It most closely resembles a neon bulb. It has two soldered in leads and the
    "spark gap" appears to be inside a gas filled glass cavity. My guess here
    is that the electrode distance is fixed and that the distance coupled with
    the type of gas inside the bulb probably determines the breakdown voltage.

    As such there is no way to clean the spark gap as you have recommended. I
    could certainly remove the device and see what happens, or find a
    replacement. I may even be able to swap it with one of the other devices on
    the CRT socket board which appear to be the same. I am leery of doing this
    though right away. I would prefer to test the critical devices first to see
    is any has drifted out of spec over time. I also would appreciate getting
    the schematic so that I can confirm the other devices are in fact the same
    value so could be swapped.

    Thanks again. Let me know if you have additional feedback or thoughts.
    Sorry for not being more clear on the type of voltage surge device being

  4. Guest

    Cleaning the spark gap isn't going to fix it.
    Those monitors are notorious for failing focus dividers on the flyback
    and capacitors going high esr in the power supply, both of which can
    cause the focus voltage to go too high and the spark gap to arc over.

    In addition the simple check is to make sure the ground pins on the
    flyback are all good. Rarely on some monitors if the divider resistor
    ground pin solder connection breaks loose the focus voltage also will
    go way high.
  5. Bob Shuman

    Bob Shuman Guest

    Thanks. I have visually inspected all the flyback pins and the solder does
    look good. I can retouch all of them as this is fairly simple with the
    board out. On the high ESR elecrolytics, which component numbers or do you
    suggest I check them all? A quick visual inspection did not yield any that
    appeared to be bulging and I did begin to test ESR on the largest PSU
    section capacitors, but they checked out low in circuit with the Dick Smith
    ESR meter.

    What I really need is the schematic so I can see what would cause the
    voltage to be high on that particular protection device. I could then
    remove leads of suspected resistors, caps, and diodes to test them correctly
    with my DMM and the ESR meter.

    But, unfortunately without the schematic I can only hunt and peck based on
    tracing the conductor paths and this is extremely difficult due to the
    density and physical layout (there are several large heat sinks obstructing
    view/access). This group has always come through for me in the past ... so
    I remain optimistic that someone will be able to help me out.

  6. kip

    kip Guest

    Ok Fine the reason I suggested clean the gap was because
    I just had one similar on an RCA TV that was in a sort of damp
    location and cleaning did the trick.Best of luck trouble shooting
    the Monitor .Most probably a bad IHVT or Focus Network if it has one.


  7. Bob Shuman

    Bob Shuman Guest

    Thanks again for the response. Just wish I had the schematic!

  8. Guest

    You don't need a schematic to troubleshoot a bad focus resistor

    This might be the info you want:

    Hopefully will help with any other potential issues.
    Be aware that if something happens to corrupt the eeprom that holds the
    alignment data, you will have to send it off for repair as hte computer
    interface and software to perform an alignment is not cost effective to
    buy for only one monitor.
  9. Bob Shuman

    Bob Shuman Guest

    Thanks ... I found my monitor, the Dell P991, on the list and successfully
    downloaded three .rar files. What application opens these? I thought they
    would be .pdf and could be read with Adobe Acrobat, but I do not think I
    have seen a .rar file before. If I can get these open then I can read what
    is there and see if this is what I need.

    Sorry to be such a pain... I do appreciate directing me here. This site did
    not come up when I did a Google search. It appears to have a lot of info
    and be from Bulgaria!

  10. Sjouke Burry

    Sjouke Burry Guest

    I just plonk rar files into winzip and that works
    for me -)-)-)
  11. kip

    kip Guest

    You need winrar to open them..
  12. Bob Shuman

    Bob Shuman Guest

    Thanks. I'll try Winzip first as was suggested, then see if I can find this
    other app if needed.

  13. Bob Shuman

    Bob Shuman Guest


    Thanks again. I downloaded winrar and also winDJview to open the .DJVU file
    that was inside the .rar archive. This contained the full service manual
    and a schematic as well so I think I am good for now.

    It never ceases to amaze me how this group always comes through.

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