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TTX 19" Monitor

Discussion in 'Electronic Repair' started by ral, Jan 2, 2004.

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  1. ral

    ral Guest

    Hello,
    I have a 4.5 year old monitor (original owner) that has no
    display/raster, power LED is good and I hear a clicking sound on power
    up. Swapped to different workstation same problem. Cleaned the dust
    out and checked for blown fuses and burned components and obvious
    arching around the flyback transformer and yoke/CRT. Scoped the
    flyback (10-pin) on the motherboard pins 1 & 2 and 5 & 6 are signals
    pins 3 & 4 are ground pins 7,8,9,10 no voltages. Noticed the horizonal
    output tansistor on heat sink not even getting a little bit warm. The
    repair facililty is within an hour of my location. The repair costs
    are $97 labor plus parts if it is not the flyback tranformer or
    tube[$35 plus tax for diagnostics].
    My question is it worth the risk to run to the repair or dump it in
    the garbage and purchase another monitor. I like the monitor and don't
    have alot of money at this time to purchase a good replacement. I was
    running the monitor on a 2-port kvm switch. The other question is
    does anybody think I have a bad flyback or CRT.

    Best regards,
    ral
     
  2. Jerry G.

    Jerry G. Guest

    With a monitor of that make and age, I would get a new one, rather than sink
    good money in to it. In a few months something else can go wrong with it.
    At least with a new monitor you will have a warranty.

    --

    Greetings,

    Jerry Greenberg GLG Technologies GLG
    =========================================
    WebPage http://www.zoom-one.com
    Electronics http://www.zoom-one.com/electron.htm
    =========================================


    Hello,
    I have a 4.5 year old monitor (original owner) that has no
    display/raster, power LED is good and I hear a clicking sound on power
    up. Swapped to different workstation same problem. Cleaned the dust
    out and checked for blown fuses and burned components and obvious
    arching around the flyback transformer and yoke/CRT. Scoped the
    flyback (10-pin) on the motherboard pins 1 & 2 and 5 & 6 are signals
    pins 3 & 4 are ground pins 7,8,9,10 no voltages. Noticed the horizonal
    output tansistor on heat sink not even getting a little bit warm. The
    repair facililty is within an hour of my location. The repair costs
    are $97 labor plus parts if it is not the flyback tranformer or
    tube[$35 plus tax for diagnostics].
    My question is it worth the risk to run to the repair or dump it in
    the garbage and purchase another monitor. I like the monitor and don't
    have alot of money at this time to purchase a good replacement. I was
    running the monitor on a 2-port kvm switch. The other question is
    does anybody think I have a bad flyback or CRT.

    Best regards,
    ral
     
  3. GPG

    GPG Guest

    Check voltages on CRT board and tell us
     
  4. John Gill

    John Gill Guest

    ral:
    The clicking usually means that the switching power supply is trying to
    start, it then detects an over-current situation (short), shuts down,
    then trys all over again.
    Have you checked the Horizontal Output Transistor (HOT) for shorts ?
    You can check this using the diode-check on your meter.

    Are you getting any secondary voltages from the power supply ?
    Any voltage on the collector of the HOT ?
    John
     
  5. ral

    ral Guest

    Hi John,

    Thanks for the reply.
    Okay I have checked the HOT in-circuit with my ohm meter. I'm reading
    shorted. The part number is (C5521.96). There is a flat pack diode on
    the same heat sink with the cathode going to the collector of the HOT
    it reads short as well. Part number 1G123S15

    ral
     
  6. ral

    ral Guest

    ral wrote:

    <snip>

    The HOT part number is 2SC5521 and I just ordered one for $17.50 If
    this doesn't fix it. I'll move the monitor to the garbage. I'll keep
    the newsgroup posted on the final resolution.


    Thx's
    ral
     
  7. John Gill

    John Gill Guest

    Ral:
    I would have taken the HOT transistor and dual-diode out of the circuit and
    tested it agin if it checked shorted in circuit. I find the diode-check
    function on my meter to be more accurate at finding shorted transistors.
    Many HOT transistors will check base-to-emitter short while in circuit.
    I usually check both combinations of base-collector and collector-emitter
    with the diode-check.
    John
     
  8. John Gill

    John Gill Guest

    ral:
    Another thought:
    Many monitors use a Field Effect transistor (FET), a capacitor, and sometimes
    a diode in a regulator circuit that supplies the primary of the flyback
    with its operating voltage. This voltage, when it leaves the primary,
    flows through the collector of the HOT. It is fairly common for the FET
    or capacitor to go bad which causes the voltage to go up and also blow
    the HOT. Check it out before you install the new HOT transistor.
    John
     
  9. ral

    ral Guest

    Good point, John I'll check everything out of circuit when the part
    gets here. I did check collector to emitter (ground) shorted on the
    HOT. Another tidbit from the OP is a closer look at the HOT showed
    burn marks on the component side of the HOT at the base, collector
    leads. I received the tracking number on the part should be 5 days.

    Thx's again
    ral
     
  10. ral

    ral Guest

    <snip>

    I received the replacement HOT and removed the bad HOT checked the
    diode and cap in the circuit good with an ohm meter. Installed the new
    HOT and tested and still no raster/display. Rechecked the HOT/diode
    with an ohm meter after power test in-circuit and still tested good.
    The electronics appeared to be working because of blinking amber led
    when video input signal removed. With power on and cover off visually
    checked heater on CRT neck and nothing. Suspect bad tube or flyback.
    Thanks to all who helped and commented.

    ral
     
  11. John Gill

    John Gill Guest

    ral:
    If the heater within the picture tube is not glowing, check the voltage
    on the heater pins of the CRT socket. Should be about 6.3 VDC.
    If not, try to follow the heater lines down into the main board. Look
    for a bad capacitor or diode.

    Are you getting any high-voltage ? Do you hear the crackle when the
    high-voltage comes up ? If not:
    1. Check the resistance between the CRT anode wire (heavy red to top of
    picture tube) and ground. Should read open circuit (greater than
    200 Meg ohm).
    2. Check the capactance between anode wire and ground. Should read about
    2.75 nano-farads. Flyback is bad if less than 1 nano-farads.
    3. I usually check the primary flyback winding with a flyback ring tester.
    But you probably do not have one.
    John
     
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