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Thread: Commodore 1084 monitor high pitched noise

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    Amiga tweaker Amibayer! Buzzfuzz's Avatar
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    Default Commodore 1084 monitor high pitched noise

    Well one of my 1084 monitors went dead and this is the second one with the same problem.

    Now researching this problem I found out trough the Big Book Of Amiga Hardware: http://www.amiga-hardware.com/showha...cgi?HARDID=849

    A loud whistling noise indicates a bad flyback transformer (also known as an LOPT). Some 1084 monitors also have digital RGB (PC clone CGA) inputs, and there was such a profusion of minor or major variations that any 1084 might have any combination of analog RGB, digital RGB, and composite inputs.
    Doing a bit more reading on EAB: http://eab.abime.net/showthread.php?t=49876

    So the flyback transformer is HR 7506 , right ?
    This is what needs replacing and BU508A.

    Have I done my homework right ?
    Wonderful Indonesia

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    Hi

    From my experience, before you invest in a flyback, please try the following:

    - Replace the HOT.
    - Look for dry/open solder joints in the high-voltage circuit area, go over everything that looks suspicious (I usually go over everything, better safe than sorry!).

    Only if that doesnt help, or the HOT gets killed again, replace the flyback.

    Btw, my experience with replacement (not original) flybacks for C= monitors has not been good so far but I cant remember if I tried HR units.

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    Amiga tweaker Amibayer! Buzzfuzz's Avatar
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    Quote Originally Posted by UberFreak View Post
    Hi
    - Replace the HOT.
    And what exactly is that ?
    Wonderful Indonesia

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    @Uberfreak: replacing the Horizontal Output Transistor will not help without replacing the flyback.

    If the HOT is dead, it take the LOPT with it.

    But from my experience the best is replace both at the same time. The transistor is indecently cheap and may save a lot of headaches salvaging the monitor.

    @Buzz: the HR7506 is the one for Daewoo monitors. Did you checked if yours are Daewoo or Philips?
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    Quote Originally Posted by rkauer View Post
    @Buzz: the HR7506 is the one for Daewoo monitors. Did you checked if yours are Daewoo or Philips?
    No, not yet, but I guess they are Philips, since these are the old 1084 versions.
    Wonderful Indonesia

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    Amibayer! UberFreak's Avatar
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    @rkauer:

    I have 2 previously repaired 1084s units which only had the HOT replaced.
    One had open solder joints on the LOPT, the other had completely dry heat-sink compound on the HOT.
    In both cases, the HOT died alone

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    But then the monitor will not make a whistle, it just sit there doing nothing with the power LED lit. Like a pc computer with windows installed.

    High pitch noise clearly indicates that a high current is passing by the primary coil of the flyback.
    David Bradley made Ctrl+Alt+Del, Gates turn it mandatory
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    Quote Originally Posted by rkauer View Post
    High pitch noise clearly indicates that a high current is passing by the primary coil of the flyback.
    Or the Chopper Transformer in the PSU being overloaded due to a short circuit Line output Transistor (HOT).

    The transistors are dirt cheap so worth trying before replacing the LOPT (flyback)

    TC
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    MAte, the problem is when the transistor goes short-circuited, it let the total DC current pass on the primary of the flyback. Much more current than the transformer can cope.

    I can say: the flyback can be cracked inside (open circuit) without damaging the transistor.

    But if the transistor is shot, then the chances are it takes the flyback with it.

    Oh, when replacing the high voltage circuit on those irreplaceable monitors, let yourself go nuts and swap the chopper transistor & high voltage capacitor on the PSU section, too. Few money to assure a long life for the repaired monitor.
    David Bradley made Ctrl+Alt+Del, Gates turn it mandatory
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    Any for anybody reading this thread, remember, you should only open a monitor if you know how to safely discharge it, as there is a danger of electric shock and death from residual charge.

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