Power Supply Tester

Discussion in 'A+ Certification' started by RF, Aug 1, 2004.

  1. RF

    RF Guest


    I have been working on this pc, (Dell Dimension 2300 2 GHz, 256 MB, 40 GB),
    and despite being only 2 - 3 years old, the inside was filthy. I cleaned it
    out very well with compressed air, afterward, it would not start, and in
    fact, would turn slightly( the fans would move), just by plugging it in.
    After I took it apart and re-cleaned everything, I was able to get the pc to
    turn on normally. I reimaged, and everything appears to be fine, However,
    today I borrowed a power supply tester, and when I tested it, one of the 5
    volt lights does not come on, (the - 5V), and overall, both the "good" light
    and the 'danger' light come on.
    Does this mean that the power supply is bad? The computer seems to be
    running fine now.

    RF, Aug 1, 2004
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  2. RF

    Mark Guest

    Could be getting ready to go....I would leave it on for a long time and see
    if it starts rebooting.
    Mark, Aug 1, 2004
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  3. RF

    RF Guest

    A side note, this is a P4 power supply. I don't know if that makes a
    difference or not.


    RF, Aug 1, 2004
  4. RF

    Danny Kile Guest

    The tester is more that likely for standard AT or ATX type power
    supplies, however, Dell uses a proprietary power supply and the pin outs
    would be different.

    Danny Kile
    Please reply to the Newsgroup ONLY

    "Dogs come when they're called, CATS take a message and get back to
    you." Mary Bly
    Danny Kile, Aug 1, 2004
  5. Howdy!

    I'd cross check - certain Dells use a non-standard wiring for the
    ATX power supply, and such will require an adapter for most ATX testers to
    work properly.

    Ralph Wade Phillips, Aug 1, 2004
  6. RF

    ric Guest

    The need for a -5v output on the PSU was removed from the ATX specification
    in April, 2003. (ver 1.3)

    http://www.formfactors.org/developer\specs\ATX12V PSDG2.01.pdf
    ric, Aug 1, 2004
  7. RF

    kony Guest

    -5V is irrelevant for a semi-modern PC, that voltage is "often"
    still implemented on an ATX only due to spec, "true"
    compatibility with some odd design never seen in typical PC. On
    a Dell or any typical system not using -5V, you can completely
    remove -5V line and expect no problem, other than a hardware
    monitor type warning "if" that voltage is monitored at all. When
    a system does not use any particular voltage rail, it is common
    for that rail to be out of spec since there is no load on it,
    unless the power supply itself has a built-in load, which isn't
    to be expected on that rail.

    Perhaps a more important question is, if everthing appears fine,
    why the further testing?
    kony, Aug 1, 2004
  8. RF

    Conor Guest

    -5V is no longer used.
    Conor, Aug 1, 2004
  9. I have a couple of mobos made in 1997 that don't use the -5V or -12V,
    so I wouldn't worry about that. But I also wouldn't trust any PSU
    tester because one I borrowed said that a PSU was OK even though its
    +12V rail was at about 10.5V and kept the HD from spinning. It's
    better to buy a cheap digital multimeter and learn how to use it
    because not only will it be a lot more accurate (2% error, worst
    case), but it can be used for testing lots of other things.
    larrymoencurly, Aug 2, 2004
  10. RF

    Franc Zabkar Guest

    I doubt it. The -12V rail would be needed for RS232.

    - Franc Zabkar
    Franc Zabkar, Aug 2, 2004
  11. RF

    kony Guest

    What year would you consider to be the *average* transition point
    towards serial drivers not needing -12V? I do think the typical
    chips from National and TI still did at beginning of '97, but
    don't know after that.
    kony, Aug 2, 2004
  12. RF

    RF Guest


    Thank you so much for your input. These newsgroups never cease to amaze me
    with their knowledge base.

    RF, Aug 3, 2004
  13. One is a 430TX mobo made by some defunct company and doesn't seem to
    have any documentation available for it on the web. The other is an
    FIC PA-2007 (VIA VP2 chipset) that uses a 5V-only Analog Devices brand
    chip to convert between RS-232 and TTL levels and contains its own
    charge pump circuitry to generate +10V and -10V for the RS-232 side.
    When I bought this mobo used, its RS-232 ports didn't work except at
    slow speeds because two .1 uF surface mount capacitors for the charge
    pump were missing. I thought they'd been knocked off during
    installation of a PCI card, but apparently they had vaporized when the
    previous owner plugged or unplugged a parallel printer or serial
    device with the power on. I know that the parallel port could do this
    because my friend later unplugged a printer from this mobo and caused
    the same capacitors to explode.
    larrymoencurly, Aug 3, 2004
  14. I have a Fluke 73 that someone gave me in lieu of cash, and even
    though it was their cheapest model it's built noticeably better than
    my no-name, which has a 250V fuse for a 600V circuit (Fluke has a
    jumbo 600V fuse wrapped in fiberglass cloth to prevent fragments from
    flying out in case it explodes), and it's supposed to be able to run
    2,000 hours on a single 9V battery, compared to just 250 hours for my
    Also some meters, even inexpensive ones, now have an RS-232 serial
    port and software to allow their readings to be monitored by a PC,
    which can be useful for checking intermittent equipment. My no-name
    has a feature that can do this by remembering the high and low values.
    The tester I borrowed has a pair of 5W load resistors for the +3.3V
    and +5.0V.
    5V through 5 ohms = 5W, and I learned the hard way that when a
    resistor is run at its full power rating, it can melt plastic and burn
    skin. Apparently, some other PSU testers are built the same way.
    larrymoencurly, Aug 3, 2004
  15. Christopher Pollard, Aug 3, 2004

  16. I keep both in my toolbox. I find the tester is most times right, and
    is good for a quick-and-dirty check of things. If I have to get into
    it more deeply, I haul out the dmm and crank it up.

    I got the PS tester at CompUSA and it's come in very handy.
    Micah Torrance, Aug 3, 2004
  17. RF

    AG Guest

    AG, Aug 3, 2004
  18. RF

    Franc Zabkar Guest

    You're right, of course. I have a FIC PA-2012 that uses the same (?)
    chip, an ADM213EARS.

    Here is the datasheet:

    I've been aware of such 5V-only chips for quite some time (Maxim also
    makes them), but until I saw the Analog Devices datasheet I was
    struggling to explain why a designer would opt for 8 charge pump caps
    and a more expensive IC instead of simply taking advantage of the
    +/-12V supply rails. It appears that this IC is powered from the 5VSB
    rail and has a low power shutdown mode in which two receivers remain
    active for wake-on-interrupt monitoring.

    In any case, your original statement that the motherboard doesn't
    "use" these negative rails can be seen to be ambiguous. A PCI-only
    board would not need the -5V rail since the PCI spec makes no
    provision for same. However, the -12V supply *is* bussed to the PCI
    slots, so the motherboard does actually use it.
    This is bizarre. I can't understand how the charge pump caps for the
    RS232 driver IC can be affected by a failure of the parallel port. On
    the PA-2012 board the parallel port is connected to a Winbond W83877F
    multi-IO chip. I would think that your PA-2007 would be similar. In
    any case, for a capacitor to vaporise, I would think that it would
    have to experience a large overvoltage. I can't imagine that an
    inductive spike from a data cable disconnection would have sufficient
    energy to cause this failure (?). If anything, I would expect the I/O
    chips to fail well before any passive component. Having said that, I
    *have* seen failures in open collector drivers (eg 7406) in 20mA
    current loop implementations of RS232 when the data cable has been
    disconnected with power applied.

    - Franc Zabkar
    Franc Zabkar, Aug 3, 2004
  19. RF

    kony Guest

    On Wed, 04 Aug 2004 06:35:45 +1000, Franc Zabkar

    The motherboard may route -12V to PCI but what uses it?
    Old soundcards with integral amp come to mind but nothing else.
    kony, Aug 3, 2004

  20. Don't have it in front of me right now, but I believe it is.
    Micah Torrance, Aug 4, 2004
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