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KDS AV-195TF No Raster

Discussion in 'Electronic Repair' started by Kirk S., Oct 12, 2004.

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  1. Kirk S.

    Kirk S. Guest

    Hi,

    Got this monitor for free and am poking arounnd inside of it.

    Power supply outputs check good.

    Unit powers up.

    Using an isolation transformer for testing, I have voltage on the HOT and
    deflection yokes. Removed HOT and it tests fine.

    No B+ at the flyback. All voltages on the flyback are null and void.

    The heater pins glow however I get no raster on the screen at all. I
    thought I had HV at first however I believe the static was from the degauss
    coil.

    Of course, I have no schematic or service literature.

    Ideas?

    Kirk S.
     
  2. Jerry G.

    Jerry G. Guest

    Do you have the proper supply voltage to the HOT?
    Is the collector of the HOT, not having an open bias?
    Are all the outputs of the power supply properly verified?
    Are there horiz scan drive pulses reaching the HOT from the scan gen?

    --

    Jerry G.
    ======

    Hi,

    Got this monitor for free and am poking arounnd inside of it.

    Power supply outputs check good.

    Unit powers up.

    Using an isolation transformer for testing, I have voltage on the HOT
    and
    deflection yokes. Removed HOT and it tests fine.

    No B+ at the flyback. All voltages on the flyback are null and void.

    The heater pins glow however I get no raster on the screen at all. I
    thought I had HV at first however I believe the static was from the
    degauss
    coil.

    Of course, I have no schematic or service literature.

    Ideas?

    Kirk S.
     
  3. Kirk S.

    Kirk S. Guest

    Jerry,

    I'm a novice, so bear with me please...

    One hand in pocket, one lead clipped to cold ground, isolation transformer
    in use, all but tip of other lead taped for insulation.

    All outputs from SMPS are clean of AC and DC matches markings on PCB.

    I followed the +210vdc to the HOT (actually a transformer near the NOT).
    Attempting to read voltages at the collector and emitter freak out my meter.
    Makes me believe there is activity. It has a separate damper diode on the
    board which also tests ok. I get a reading on the base of about 0.4 vdc. I
    have a scope however I'm apprehensive to hook it to anything. I've just
    used it to probe digital circuits; never anything with voltage. I should be
    able to hook it to the base of the HOT and see the horizontal pulses,
    correct? I understand that I don't want to connect it to a hot ground (line
    voltage).

    Am I correct in the assumption that manufacturers label different circuits
    with different numbers? ie. IC4xx, R4xx, Q4xx, C4xx is one area
    (Deflection on this monitor) and IC9xx, etc. is another? The flyback is
    T901 and I'm looking around (with monitor off) at the 9xx related components
    to see if I can find something.

    Can I safely look at the yoke voltages with a scope? Or do I need to find
    them before they are amplified?

    Interested in learning yet very respectful of the voltages inside. I also
    have a high voltage probe so I can test the anode voltage if necessary. I
    have fixed a couple arcade monitors however the flyback is connected to the
    HOT on those and this multifrequency monitor is quite a bit more
    complicated.

    Thanks!

    Kirk S.
     
  4. Kirk S.

    Kirk S. Guest

    Jerry,

    I found a bad fusible resistor on the B+ line to the flyback. I just needed
    to look at it differently and follow the path back from the flyback to the
    power supply. Will check other components in the area as well.

    Kirk S.
     
  5. Kirk S.

    Kirk S. Guest

    Update:

    Replaced 1/2 Watt 0.22 Ohm FP resistor and the monitor fires up.

    Two dead monitors: $1 worth of parts, several hours of my spare time and
    help from those here has got me back going again.

    Thanks to all!

    Kirk S.

    P.S. It helps me to look at a monitor like a car; pretty complicated when
    you look at the whole thing however once you break it down into each system,
    it isn't nearly as bad.
     
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