Power supply, but no power???

Discussion in 'IBM' started by U. Cortez, Apr 7, 2005.

  1. U. Cortez

    U. Cortez Guest

    I believe a power surge toasted my power supply the other day, so I
    replaced it with a new 350W ATX PSU. After removing the burnt psu, I
    screwed the new psu into the case, hooked the ATX power supply to the
    motherboard, and hooked up power for various components (HD's,
    CD-ROM's). The motherboard's pilot light turns on to signify that it's
    getting power, but when I press the case's power button... nothing. No
    fans, no sound, no disk spinning, no signs of life at all (besides that
    pilot light being on). Am I forgetting something?

    I inspected all the components (and the motherboard and cpu) and none
    of them appear (or smell) to have been damaged.

    Where do I go from here? Any help would be appreciated.

    Motherboard: DFI AK70 (AMD 750 cpu).


    PS, forgive the cross-post -- I don't have a news host and google is
    giving me errors when I try to post to some of these groups
    U. Cortez, Apr 7, 2005
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  2. U. Cortez

    Wes Newell Guest

    Double check the power button plug is plugged into the proper pins. If it
    is and it still doesn't work, unplug it and short the 2 power button pins
    on the MB for a second. It should turn on power. If not, then it may be a
    bad MB or bad PSU. If it does come on that way, then the problem is in the
    leads to, or the power button itself.
    Wes Newell, Apr 7, 2005
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  3. U. Cortez

    w_tom Guest

    If the power supply is toasted, then you have an important
    fact. What inside the power supply is blackened? However if
    just assuming it was some surge and if assuming it was the
    power supply, then you have much to learn. The power supply
    'system' is many components. A power supply is only one
    part. You could swap things forever until something works.
    Or discover in but two minutes what is and is not damaged.

    Procedures and concepts are provided in two previous posts:
    "Computer doesnt start at all" in alt.comp.hardware on 10
    Jan 2004 at
    http://tinyurl.com/2t69q and
    "I think my power supply is dead" in alt.comp.hardware on 5
    Feb 2004 at

    Just because a light is on does not mean sufficient voltage
    is available. Lights can illuminate; fans spin; and still the
    power supply is not working. But then a power supply might
    shutdown because something else is defective. There is no
    faster analysis than using a 3.5 digit multimeter. Two
    minutes should suggest what is defective. Furthermore,
    numbers that mean nothing to you could be the 'smoking gun'
    solution for those with better knowledge. Without numbers,
    you cannot tap the best sources on the other side of your
    computer screen.
    w_tom, Apr 8, 2005
  4. U. Cortez

    U. Cortez Guest

    Thanks for the reply.
    Yes, I know the PSU is toasted. Whether or not anything else is
    damaged is what I don't know. I haven't bothered opening up the power
    supply itself... and other than recognizing what resistors and
    capacitors are, I'm not real familiar with the components _within_ a
    psu. I don't know what caused the problem, but the circuit breaker was
    thrown for the entire room (not only did computer shut down, all the
    lights and clocks turned off, etc). However, it wasn't a brown- or
    That'll be my next step. Thanks for the info.
    U. Cortez, Apr 8, 2005
  5. U. Cortez

    pobo88 Guest

    try taking all of the components out of your computer and runniong the
    system out of the case, at least this mught remove the chance that
    something is grounded.
    pobo88, Apr 8, 2005
  6. U. Cortez

    U. Cortez Guest

    If the power supply is toasted, then you have an important
    Just for kicks, I opened up the old psu and it looks like a couple
    capacitors blew. I'm not going to be all that dissappointed to see
    that psu taken to the morgue, as it was old and cheap and possibly
    under-powered. However, I won't be a happy puppy if my motherboard got
    toasted too. I'll probably test it today and see...

    U. Cortez, Apr 8, 2005
  7. U. Cortez

    w_tom Guest

    The failed capacitors (and probably failed diodes) is
    consistent with the circuit breaker tripping. Now here is
    where we discover the technical knowledge of the guy who
    selected that supply. Asian manufacturers have learned there
    are many computer assemblers masguading as electrically
    knowledgeable. So power supplies that are missing essential
    functions are now dumped into the market at greater profit.
    You know them by their lower price. These are functions where
    were defacto standard even 30 years ago.

    Any power supply that fails must not damage any other
    computer part. But if the essential function was missing in
    that supply, then you now may have other damage. A minimally
    acceptable supply sells for about $65 full retail. Supplies
    missing essential functions such as overvoltage protection
    sell for less, earn greater profits for their manufacturers,
    and can then cause disk drive and motherboard failure.

    You have no other failures inside the computer IF the
    original power supply was minimally acceptable; not selected
    by a 'bean counting' computer assembler.
    w_tom, Apr 8, 2005
  8. U. Cortez

    Wes Newell Guest

    I think overload protection is a requirement for UL approval. And I've
    never spent over $24 for a PSU.:)

    I've used a 600W similar to this for over a year now on my A64 system. But
    it was $24 when I bought mine.

    Wes Newell, Apr 8, 2005
  9. U. Cortez

    DaveW Guest

    It sounds like the power surge also toasted your motherboard. This
    frequently happens when an inexpensive power supply unit is used in a
    system. It passes the surge on to the motherboard, rather than absorb it
    DaveW, Apr 9, 2005
  10. U. Cortez

    U. Cortez Guest

    Well last night I tested the power supply (with it just plugged into
    the motherboard) and all the voltages were in their acceptable ranges.
    So, I started to plug things back in 1 at a time, and... it all
    worked! I'm typing this now on my working computer. There must have
    just been a loose connection or something when I first installed my new
    PSU. But when I took my computer apart (yes, I mean completely apart
    -- even took the cooler off the cpu) and put it back together I must
    have secured whatever was keeping it from starting up before.

    So I guess the failed motherboard was a false alarm (whew!). Now the
    first thing on my agenda: get a UPS so I don't have to worry about
    circuit trips blowing my PSU again.

    Thanks all for the help!

    U. Cortez, Apr 9, 2005
  11. U. Cortez

    Franc Zabkar Guest

    I'd be suspicious of that 600W rating. The combined output of the 3
    major rails is 644W, a figure that doesn't appear to allow for proper
    derating. If it's a Deer brand PSU, I'd be looking especially closely
    at it. I've been stung by a 170W fake labelled as 400W.

    Here are the claimed specs from the above URL:

    ATX 600 Watt Power Supply for P4 ,PIII and AMD processor compatible
    with ATX 2.03 standard.

    DC Output:

    +5V 50A +/-5% +3.3V 32A +/-4% +12V 24A +/-5%

    -12V 1.0A +/-10% -5V 0.5A +/-10% +5Vsb 2.0A +/-5%

    Having said the above, I'd be willing to bet that the PSU in a typical
    system is never called upon to provide more than about 150W.

    Until my recent experience with the fake PSU, I've always been well
    served by generics. In fact, I contacted a dozen or so computer stores
    in my area and was unable to find a single vendor who could supply
    anything other than a generic ATX PSU. Most were selling Deers. I had
    to go online to find a branded PSU.

    - Franc Zabkar
    Franc Zabkar, Apr 9, 2005
  12. U. Cortez

    w_tom Guest

    Overvoltage protection is not required for UL approval -

    First, power supplies selling for $25 retail would quickly
    forget that essential function. If is contains essential
    functions such as overvoltage protection, then the
    manufacturer would proudly note that function - and many
    others. If is does not list overvoltage protection (as with
    most sub $40 supplies), then it will also forget to install
    overvoltage protection and many other essential functions.

    Second, just not possible to sell a supply at $25 retail,
    earn a profit, and include essential functions.

    Third, UL only cares about you getting hurt. UL does not
    care for an instant how destructive that power supply is to
    any transistors. Overvoltage protection does nothing for
    human safety.

    Fourth, then there is the common problem with counterfeit UL
    stickers. No way a $25 supply is going to include functions
    considered essential even 30 years ago.
    w_tom, Apr 10, 2005
  13. U. Cortez

    w_tom Guest

    Problem could even been created by a motherboard standoff
    shorted through solder mask. Example of why one does not swap
    parts. You fixed (permanently or temporarily) the problem and
    don't even know why it existed. In the future, get the
    numbers before disassembling anything. At least we would have
    a much short list of suspects. If failure is seen on meter,
    then you could disconnect some things and test until the
    problem is resolved. Knowing which voltage was problematic
    could have also been more helpful.

    Just a better way to approach the problem next time.
    Historically, such intermittents tend to return slightly more
    often than not.
    w_tom, Apr 10, 2005
  14. U. Cortez

    Wes Newell Guest

    So, you don't think they could spent an extra 25 cents to do this in a $25
    PSU. Interesting.
    Again, if you say so.
    Well, This psu says it has overload protection, and I have no basis for
    calling them liars. It's retail price is over $40, but it's sale price is
    only $18. They also have a 300W unit that states it has overload
    protection they sell for $9 (Retail price of $24).

    Wes Newell, Apr 10, 2005
  15. U. Cortez

    U. Cortez Guest

    I think you both have a point. I have no doubt that there are cheap
    psu's out there that completely ignore the need for overvoltage
    protection. On the contrary, there are probably some inexpensive psu's
    that have the protection. While it appears that the psu that wes found
    does have protection, I'd still be a little skeptical of a psu that
    claims to push 600w but only cost $18. Personally, I'll stick with
    name-brand psu's.
    U. Cortez, Apr 10, 2005
  16. U. Cortez

    w_tom Guest

    Overload protection is another and different function
    required of power supplies. Does that $25 supply really have
    overload protection? The specs are quite clear about this.
    Short all outputs together and turn on power. Power supply
    must not be damaged. That demonstrates overload protection
    which is completely different from overvoltage protection
    which, in turn, has nothing to do with UL approval.

    This is basic electrical knowledge that anyone should
    understand before making power supply recommendations.
    Overvoltage and overload (or overpower) protection are
    completely different functions. Power supplies must meet
    both, and other standards such as FCC. Just another standard
    that many discounted power supplies may violate to sell at
    w_tom, Apr 10, 2005
  17. U. Cortez

    Franc Zabkar Guest

    In fact the additional cost can be nil. Deer PSUs have a single IC
    that does it all - PWM control, PS-ON control, +3.3V regulation,
    +5/+12V regulation, Power Good generation, and overvoltage sensing.

    See this circuit diagram:

    "LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."

    - Franc Zabkar
    Franc Zabkar, Apr 10, 2005
  18. U. Cortez

    Franc Zabkar Guest

    Here is the data for an all-in-one IC (not the same as in the Deer

    - Franc Zabkar
    Franc Zabkar, Apr 10, 2005
  19. U. Cortez

    w_tom Guest

    I don't see the overvoltage protection circuit anywhere in
    that power supply at electro-tech.narod.ru . Overvoltage
    protection means something must be able to short out a (about)
    25 amp output with no damage. Not a cheap component and
    definitely not possible inside an Integrated Circuit.

    The IC SG6105 contains many functions previously performed
    by multiple chips. This is a minor cost decrease. But, for
    example, the galvanic isolation necessary for some of those
    functions is not inside this chip either. Things such as
    optocoupler are still another separate component.
    Overvoltage protection is not a part of that chip. In fact,
    Intel specs demand that overvoltage protection be part of a
    separate circuit.

    The SG6105 does contain circuits once provided by multiple
    inexpensive components. A power supply once selling for less
    than $100 now costs only $65 retail. Expensive components are
    still required for other and necessary functions such as
    overvoltage protection. Supplies containing necessary
    functions such as overvoltage protection cannot sell for $25
    retail at profit. Those would be supplies dumped into the
    market missing essential functions.
    w_tom, Apr 11, 2005
  20. U. Cortez

    Franc Zabkar Guest

    The chip senses all the rails, including the negative ones, and shuts
    down the oscillator if there is a fault condition. No oscillator means
    no output. AFAICS, there is no need to crowbar the affected rail(s).
    Pins 3,4, and 6 provide the OV functions. Pin 5 is probably equivalent
    in function to the OPP (over power protection) pin of the SG6105.
    Crowbar SCRs/zeners were used in the old days with linear supplies,
    but these days most supplies are switchmode. The crowbar would protect
    the load from a shorted pass transistor by blowing a fuse, but IMO a
    switchmode supply doesn't really need such protection, unless there is
    a possibility that the OV sense circuitry itself could fail.
    The chip's datasheet states that the chip performs under- and
    overvoltage sensing/protection, as well as overpower and short circuit
    protection. The overpower pin (OPP) requires some inexpensive external
    components including a diode and some passives.
    True, but I suspect Intel is just playing it safe. I have no problem
    with a single-chip PSU, especially if the cost savings could be
    applied to properly rated parts, particularly the capacitors, diodes,
    and magnetics on the DC side.
    I don't recall seeing any such expensive components in any PC SMPS.
    All the PSUs I've seen shut down the PWM controller if there is an OV
    condition, but then I've only ever seen generic PSUs. What components
    do the more expensive branded PSUs use?

    - Franc Zabkar
    Franc Zabkar, Apr 11, 2005
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