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case power switch replacement

Discussion in 'PC Hardware' started by Haines Brown, Apr 6, 2008.

  1. Haines Brown

    Haines Brown Guest

    I just purchased a nice Lian Li case and installed into it some spare
    parts to build a system. There was a problem booting the system (see my
    other message). While working on this problem, the front power switch
    ceased to function.

    That is, when I toggle the switch on/off by pressing it, and with the
    wires disconnected from the MB, there is an open circuit in both
    states. However, if I depress the switch half-way, there is a low
    ohm reading.

    So the switch looks bad. It looks easy enough to replace, and a lot less
    expensive and troublesome than trying to find packaging for the case and
    returning it to the vender (NewEgg). I wrote Lian Li to ask for a
    replacement switch or to tell me who makes it, but I'm not optimistic
    I'll hear a reply.

    These switches must be made in great quantity. It is a SPST switch that
    toggles ON/OFF each time you press it. A simple white plastic body is
    inserted through a 32 mm. square hole in the front of the case. They
    probably are called subminiature push-button switches.

    Does anyone have any knowledge of these switches, such as the extent
    they are a standard item and who might make them? Pouring through my
    Allied catalog didn't help.
    Haines Brown, Apr 6, 2008
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  2. Haines Brown

    Arno Wagner Guest

    That would be very surprising and require a modified mainboard.
    These switches are typically on when pressed and off when not
    The plastic cap is usually not part of the switch. For the
    switch you will likely have to get soemthing similar and adapt.

    Arno Wagner, Apr 6, 2008
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  3. Haines Brown

    Haines Brown Guest

    Ahaa! Again my ignorance has betrayed me. You are quite right: When the
    switch is depressed, it closes the circuit; when released, the circuit
    is open.

    So now I'm back to my original - well, not original, but the subsquent
    problem. Originally when I booted, all I got was the MB spash
    screen. Then, after turning the machine on its side, when I pushed the
    start switch, nothing at all happens. The MB LED lights when the power
    line is connected (no matter which position the PS toggle is in), but
    nothing else happens: no fans, etc.

    I guess the next thing would be for me to test power out. I find that
    when I push the on switch, I get no +5/+12 V out from the peripheral
    power connections. I suppose this could be due to a) blown fuse in the
    PS, b) a short causing the supply to shutdown, c) a broken power
    supply. Am I correct to assume that the power to peripherals always
    comes right on whenever the power switch is depressed?

    a) I guess I can't replace the fuse without voiding my warrantee. I
    measured the resistance across the line voltage socket and got only 0.04
    ohms, which strikes me as suspicious.

    b) A short is possible. The power went after I had turned the machine on
    its side. The stand-offs holding the MB seem tall enough and don't
    believe I put any pressure on the MB backplate. I suppose I could
    disconnect everything to eliminate the possibility of a short outside
    the PS and see what happens. I gather to test supply voltages, I have to
    make sure the supply has a load of some kind. Is a connection to power
    the motor of one hard disk enough of a load?
    Haines Brown, Apr 6, 2008
  4. Haines Brown

    Arno Wagner Guest

    Yes, but the swiotch actually runns to the mainboard and the PSU
    is controlled by the MB as well. This allows swicthing off
    under software control.
    Indeed. But unless you have a special low-Ohm meter, you cannot
    measure a resitsance this low. I suspect a wrong meter setting.
    You can test most PSUs without load, if the are on only for a short
    time. A disk motor is quite enough, if you want load.

    Arno Wagner, Apr 6, 2008
  5. Haines Brown

    Haines Brown Guest

    Dunno. The DMM I have switches scales automatically.
    Thanks. If the PS fan doesn't even come on, I'm not very optistic that
    anything much else is working. I'm about to buy a reasonably inexpensive
    duplicate PS so that I can test by substitution.
    Haines Brown, Apr 7, 2008
  6. Haines Brown

    Haines Brown Guest

    W_Tom very kindly passed along a test procedure for a power supply that
    was far in advance of the primitive notions I had been carrying with
    me. His procedure is found at:

    It involved the measurement of the voltage at various pins of the molex
    main board power connector while the system was under full load.

    At all test points, I got zero voltage. There's 117VAC at the power
    cord; the power supply toggle toggle switch is in the 1 vs. 0 position;
    the mainboard LED is lit; no voltage at the front panel power switch.

    I thought the problem was this front panel switch, and contacted the
    case manufacturer about it. I'm happy to report that the manufacturer,
    Lian Li, was very responsive. I'm happy to say that a replacement switch
    is in the mail, even though it turns out that the probem is in the
    supply itself.

    At one point, although I can't repeat it today, if I press the front
    panel switch, hold five seconds, release for five seconds, and repeat
    this, on about the third try the cpu fans makes a few rotations.
    Haines Brown, Apr 9, 2008
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