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CRT monitor modeswitching

Discussion in 'Misc Electronics' started by Halfgaar, Apr 15, 2004.

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  1. Halfgaar

    Halfgaar Guest

    I was wondering, is modeswitching harmful for a CRT monitor? And when I say
    harmful, I mean that when you mode switch about a dozen times an hour, that
    an average second-hand monitor will only last a month? I ask, because I
    friend of mine switches back and forth from Linux textmode to GUI-mode, and
    he has destroyed two second hand monitors in a relatively short time; the
    second within a month, the first I don't know. I asked if he had grounded
    them to an earth, and he had.

    And another thing; in some monitors, you can hear relays switching when the
    monitor switches mode. What is this, and why do some monitors do this, and
    others don't? Someone once told me that a when a monitor has such a relay,
    that it is a sign of quality. Is there any truth to that?

    TIA
     
  2. Myron Samila

    Myron Samila Guest



    I remember seeing old MAG monitors with an LED display (digits) telling you what mode it
    is in currently, it could save 10 modes I believe for various resolutions.

    It had a relay.

    Well you figure, when you turn on your computer at POST, it is in a different resolution,
    when I boot up Winslows, it changes resolution again, when I play my favorite games, it
    changes to an even higher resolution. My monitor was made in 1994!!!!!! (archaic piece
    of junk, pre Energy saver), and it is still kicking!!! (on this machine, which is used
    daily)

    Could be just coincidence.

    I suppose resolution modes can be switched via "soft" switching, or relays, mine uses soft
    switching and hasn't ever failed (Daewoo near flat CRT)
     
  3. Jerry G.

    Jerry G. Guest

    Some models use a relay to switch some component configurations in the scan
    circuits for the different scan rates. There is nothing wrong with this. The
    newer monitors use electronic switching.

    In a properly designed monitor, there is no excessive wear by changing
    modes. The fact is, that since you are using older monitors that are used in
    the first place, the failure rate is probably higher because of age, not how
    they are being used.

    It is a fact that these monitors will run for only a certain amount of hours
    in their lifespan. There is something called MTBF "Mean Time Between
    Failure". In the lower end of the monitors, this factor is not published.
    Usually manufactures will not make a determination of this spec, because
    there is an added R&D cost involved. They are only interested that the
    monitor will last a bit more than the warranty period.

    The MTBF for most of the CRT's (picture tubes) is about 30,000 to 40,000
    hours. Under normal use, this is about 4 to 6 years. The life span of the
    electronics to keep up their performance is about the same. This is why
    after about 4 years, if the monitor is still working properly, it is a good
    idea to sell it while it is still working. This is how you can find
    so-called good deals on monitors, which in reality it is not a good deal,
    because it has reached its MTBF factor.

    If you were to buy a new monitor, you will find that you can run it for a
    bit more than 4 years with reasonable reliability. After that period the CRT
    may be a bit soft, and the scan accuracy may not be the same as when new.

    --

    Greetings,

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


    I was wondering, is modeswitching harmful for a CRT monitor? And when I say
    harmful, I mean that when you mode switch about a dozen times an hour, that
    an average second-hand monitor will only last a month? I ask, because I
    friend of mine switches back and forth from Linux textmode to GUI-mode, and
    he has destroyed two second hand monitors in a relatively short time; the
    second within a month, the first I don't know. I asked if he had grounded
    them to an earth, and he had.

    And another thing; in some monitors, you can hear relays switching when the
    monitor switches mode. What is this, and why do some monitors do this, and
    others don't? Someone once told me that a when a monitor has such a relay,
    that it is a sign of quality. Is there any truth to that?

    TIA
     
  4. Halfgaar

    Halfgaar Guest

    My few months old Eizo T766 19" CRT also uses a relay. At least, I hear
    something ticking when switching mode. But, not always. Only when switching
    from certain modes to certain others.
    It was not about my monitor(s), but a friend's.
    I know of the MTBF rating. The MTBF of a Philips 109P40 I used for a year
    (long story) had one of, I qoute, ">75000 (CRT excluded)". Strangly enough,
    I can't find anything about an MTBF rating of this Eizo model, even though
    I remember having seen it somehwere, but perhaps I'm confused with the
    109p40. Anyway, one cannot say that this is because Eizo is lower end and I
    excpect it to last as long or longer than a Philips 109P40. Both of them
    BTW have a automatic color calibration to compensate for wear of the CRT.
    And as for the loss of scan-rate precision; isn't it so that when a CRT
    starts to loose scan-rate precision, it'll be dead soon?

    My Eizo BTW has a Sony Trinitron CRT, do you know anything about it's MTBF?
    I can't find it anywhere.

    And as for the failings of my friends monitors, I'll tell him what you said.
     
  5. Bob Myers

    Bob Myers Guest

    Not without a special cathode, it isn't. With a standard
    cathode of the type typically seen in monitor CRTs, the
    mean-time-to-half-bright (the tube itself generally is spec'ed
    in MTHB, since aging of the cathode/phosphor is the
    dominant wearout mechanism, once the "infant mortalities"
    are out of the picture) is about 10-15k hours. However,
    with average use (call it about 2,000-2,500 hours per
    year), you're still in the 4-6 year ballpark. A tube left
    on round-the-clock, of course, doesn't make it that
    long.

    Most often, the relays you hear are switching components
    in and out of the horizontal deflection circuits, to set up
    for different sweep frequency ranges. More recent monitors
    tend to do that sort of switching electronically, but it makes
    little difference one way or another. There IS a bit more stress
    on the monitor when switching modes, but the effect on the
    overall life expectancy is generally insignificant. If you're
    just switching a half-dozen times an hour, I wouldn't worry
    too much about it.

    Bob M.
     
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