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Sceptre X9G Komodo monitor - Identifying a transistor

Discussion in 'Electronic Repair' started by [email protected], Sep 24, 2009.

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  1. Guest

    I'm developing a love / hate relationship with SMD devices. I love
    them when they work, and even when a parts list is available. When
    they don't, and one isn't, they cause a lot of grief.

    This particular project is a Sceptre X9g Komodo VII A monitor. This
    is a 19" LCD monitor. I'm the second person on the project. The
    first earned my admiration by reassembling the monitor after pulling
    the power supply / inverter. He even left all the screws in the
    appropriate holes!!

    After reassembling the monitor for test purposes I discovered it
    briefly (about 1 second) dimly flashed something on the screen, then
    blanked it. After some exploration, I located a bad solder joint on a
    film capacitor in the inverter. Resoldering this didn't fix it, it
    seems two transistors are shorted base-emitter. For what it's worth,
    this design is similar to the inverter used on Dell E172FPb and
    E173FPb monitors. A significant difference, the Dell uses through
    hole transistors (2SC5707), the Sceptre uses SMD devices.

    The transistors are in a package equivalent to a Sanyo PCP
    http://datasheet.digchip.com/413/413-01319-0-2SD2099.pdf The
    transistors have identification that looks somethng like this:

    DK
    o_
    QH

    I suspect that these markings identify the manufacturer, the
    manufacturer's code for the particular component, and possibly a date
    code. Needless to say, none of the SMD identification lists show a
    device using either of these codes in a similar package. I started
    with Sanyo because they make the transistors used in the Dell monitors
    mentioned above. Unfortunately, while Sanyo DOES use the DK code on
    their PCP package, the datadheet indicates this is a recent addition
    to their product line; this monitor was built in 2005.

    Using the 2SC5707 I have been able to make an approximate
    determination of the characteristics I am looking for, but searches
    are handicapped by the myriad packages used by various manufacturers.

    Any suggestions would be much appreciated.

    PlainBill
     
  2. Franc Zabkar

    Franc Zabkar Guest

  3. Guest

    Frank,

    Thanks, I'd already found that information. There are reasons to
    believe that is not the proper part.

    1. The power supply / inverter circuit board has a 12/01/2003 date on
    it; the monitor was built in May, 2005. Sanyo indicates the PCP1201
    has a status of 'New'.

    2. AFTER posting this appeal I found pictures of two inverters from
    Compaq TFT5010 monitors. These use the identical circuit (but a
    different layout). One of the inverters has 4 transistors labeled DK
    QH. The other has 4 transistors labeled DK QG. My initial conclusion
    was the QG / QH is a date code. The QG is used on the same package
    for the 2SC6096

    Wahoo!!! The package is SOT89. Mouser Electronics' search engine
    shows tiny pictures of the components that match your parameters. I
    found a PBSS4480X is available in the proper package and appears to
    have (superficially) the proper specs. Now to see if the package
    markings match.

    Thanks,

    PlainBill
     
  4. Franc Zabkar

    Franc Zabkar Guest

    It could be a Sanyo 2SD1628:
    http://www.datasheetcatalog.org/datasheet/sanyo/ds_pdf_e/2SD1628.pdf

    - Franc Zabkar
     
  5. Guest

    Franc,

    That seems VERY likely. Thank you very much!!! This is turning into
    a great day!!!

    Replace spark plugs in Wife's van (saving $150 over the dealer's
    price)

    Minnesota beats Northwestern 35 - 24

    Find the correct replacement part to repair a monitor.

    Thank you very much

    PlainBill
     
  6. Guest

    Frank,

    Well, another problem has raised it's ugly head, and I've finally
    firmly established the source of these transistors. The Sanyo part
    you tentatively identified was unavailable from my US sources. After
    some research, I decided a dxt3150-13 would be an acc3eptable
    substitute, so I ordered some. Since the original caps in the monitor
    were Elite brand (a known 'bad' manufacturer), I ordered replacements
    for them from the same distributor. Before placing the order, I
    established the monitor would behave in the expected way with the
    shorted transistors removed. I also tested the transformer to ensure
    it was not defective.

    With the shorted transistors installed, the screen would flash dimly
    for a few seconds, then go blank. After they were removed, the screen
    would come on for a few seconds, then blank. (This is the normal
    result of the protection circuits shutting down the inverter because
    of insuffficient output). When the replacements arrived, I soldered
    in the new transistors and tested it. It worked perfectly for a few
    minutes, so I shut it down and began to replace the questionable caps.

    After recapping, the intermittent dim flashes returned!!! However,
    neither the original nor the replacement transistors are shorted. It
    is a puzzlement; I'll be using a scope to see if I can figure out the
    problem.

    In the meantime, I had received a Viewsonic VX910 monitor. The owner
    indicated it was having difficulty turning on, but would eventually
    start. Rather than try to verify this, I simply opened up the
    monitor, and found three obviously bad caps. These were Capxon, also
    notorious for premature failures. And while I was at it, I replaced a
    fourth Capxon capacitor, in the inverter circuit. When I turned it
    on, it gave the smae symptoms as the Sceptre monitor. And the
    transistors were not shorted.

    Researching the Viewsonic, I found it was sold in Germany as a
    Belinea, and a complete service manual (including schematic and parts
    list) was available for download. What's more, both the Sceptre and
    Viewsonic used the same design for the inverter!! Browsing the parts
    list, it turns out the transistor in question is a Rohm 2SC4672. DK
    is the part identifier, Q indicates the gain range, and K appears to
    be some sort of production or date code.

    PlainBill
     
  7. Guest

    There is a tenedency to say that because two events (no display on two
    monitors) occured after a pair of similar events (replacing the caps
    on the power supply / inverter boards for the monitors), there must be
    a common cause. Well, there was, but it was biological in nature, not
    electronic. The scientific term would be 'incompetent technician'.

    On the Sceptre monitor, reseating the connections for the CCFLs solved
    the problem. It is currently undergoing a 'burn in' phase prior to
    being reassembled.

    On the Viewsonic monitor, testing the transistors showed that a pair
    of them are shorted. And since there were none of the characteristic
    probe marks on them, the logical conclusoin is that I INTENDED to test
    them, but neglected to.

    PlainBill
     
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