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B&W monitor - dim picture

Discussion in 'Electronic Repair' started by Chris, Jan 23, 2004.

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  1. Chris

    Chris Guest

    I have a 1995 vintage closed circuit television monitor which is
    probably from some kind of a security system.

    It has a very dim picture. The picture looks ok, but I can
    only see it if the contrast and brightness are maxed out
    and the room lights are low.

    I found an adjustment marked "sub bright" and fiddled with
    that. The picture didn't seem to get any brighter overall,
    but the blacks got "white" and the whites got wierd, kind
    of like a photographic solarization look. There are 4 video
    inputs, and the screen can alternate between a single and a
    quad view. It doesn't seem to matter which input I use.
    The subtitle dates, etc. are all dim too.

    My question is: is it likely there is just an out-of-spec
    resistor in there somewhere? or is it a slam dunk
    that the tube is shot? If there is a reasonable chance to
    resurrect the thing I'd like to know before I spend a lot
    of hours on it. Otherwise I'll put it in the pile
    to cannabalize for other projects.

    If it helps, the picture tube says Samsung 440CWB4(Q).
     
  2. Tim Auton

    Tim Auton Guest

    You don't mention any of the history of this screen. If it's been
    switched on for the bulk of the time since 1995 (quite probable for a
    security camera screen) then it's likely the tube is shot. Bin it.


    Tim
     
  3. Sofie

    Sofie Guest

    Chris:
    Based on your description of the symptoms "it is a slam dunk that the tube
    is shot"
     
  4. Jerry G.

    Jerry G. Guest

    You are giving the common description of a tube being warn out. The monitor
    is a bit old. To check the performance, you can take voltage readings and
    measure the waveforms to the elements of the tube and verify them to the
    service manual.

    --

    Greetings,

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


    I have a 1995 vintage closed circuit television monitor which is
    probably from some kind of a security system.

    It has a very dim picture. The picture looks ok, but I can
    only see it if the contrast and brightness are maxed out
    and the room lights are low.

    I found an adjustment marked "sub bright" and fiddled with
    that. The picture didn't seem to get any brighter overall,
    but the blacks got "white" and the whites got wierd, kind
    of like a photographic solarization look. There are 4 video
    inputs, and the screen can alternate between a single and a
    quad view. It doesn't seem to matter which input I use.
    The subtitle dates, etc. are all dim too.

    My question is: is it likely there is just an out-of-spec
    resistor in there somewhere? or is it a slam dunk
    that the tube is shot? If there is a reasonable chance to
    resurrect the thing I'd like to know before I spend a lot
    of hours on it. Otherwise I'll put it in the pile
    to cannabalize for other projects.

    If it helps, the picture tube says Samsung 440CWB4(Q).
     
  5. It's a slam dunk the tube is bad. The classic 1950's textbook
    description of a weak tube is "The whites turn silvery without any
    increase in brightness."

    . Steve .
     
  6. Last resort: boost the CRT filament voltage 10 or 20 percent and see
    if that helps.

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
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    Important: The email address in this message header may no longer work. To
    contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  7. Sofie () wrote:
    : Chris:
    : Based on your description of the symptoms "it is a slam dunk that the tube
    : is shot"

    I wouldn't bet the farm on it.

    Although it's possible the tube is bad, I've worked on a number of cc
    monitors like GBC and the symptoms can point to bad caps.

    Before you toss it, eyeball the chassis and see if there are any caps with
    odd values, like 47uf @350v, not the mylar ones, the electrolytics. Usually
    have high voltages, [email protected] is another one (also [email protected]).

    They have come up with some weird circuits in those things for sync
    separators and video coupling. I'd try to replace the 3 or 4 oddballs and
    cross your fingers.

    Even though they may have been in use for 10 years, those usually aren't
    standard picture tubes in those things. They go bad but not as often as
    regular tv's. Burn-in is far more common than weak tubes.

    One other thought, just for yucks also check the neck assembly for high
    value resistors (270k, 330k), these too, if they open can cause a gassy pix.

    -bruce
     
  8. Chris

    Chris Guest

    Thanks for the info!

    Chris
     
  9. Bob F.

    Bob F. Guest

    The tube is bad, the contrast switch doesn't work, so you MUST sell this on,
    where else?, eBay!
    Here's a possible listing you can try:

    "Vintage, mid-90's, rugged computer monitor, B&W, works good! Useful
    for home or office security systems, camera not included!
    Minimum bid - $40 (not including shipping) OR
    Buy it NOW - $35"

    Damn, now that's marketing!!
     
  10. James Sweet

    James Sweet Guest


    I wouldn't give up completely yet, at least check to see if the contrast
    control circuitry is working, it *could* be just an open resistor, I agree,
    probably the tube, but worth spending a few minutes to find out.
     
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