Re: Computer turns on and then just dies

Paul <[email protected]> wrote:

> On Fri, 11/22/2024 12:28 AM, VanguardLH wrote:
>> Paul <[email protected]> wrote:
>> 
>>> ...
>>>
>>> 2) Use a clamp-on ammeter, to monitor the +5VSB wire on the main cable.
>> 
>> For typical clamp meters, those rely on alternating current to fluctate
>> the magnetic field around the conductor; i.e., the common clamp meter
>> just measures AC.  The 5V standby line is DC, not AC.  With the
>> 20/24-pin connector from PSU pushed onto the mobo (to account for any
>> load), use a voltmeter to measure DC voltage from the +5VSB line (pin 9,
>> purple) to a ground pin (black).
>> 
>> I can't think of any AC inside the computer excluding the input circuit
>> in the PSU.  Power into the PSU is AC.  All lines out of the PSU are DC.
>> 
>> DC also induces a magnetic field around the conductor, but not a
>> fluctuating magnetic field.  An AC clamp meter using a transformer wound
>> through the closing fingers of the clamp won't work on a DC wire.  For
>> DC, a Hall effect sensor can measure the magnetic field: the magnetic
>> field induces a current in the sensor.  However, those are inaccurate.
>> When measuring hundreds of amperes passing through a conductor, you
>> don't care if the actual current is different by several amps.  When
>> measuring 20A, or especially milliamps, the reading in the meter is so
>> inaccurate that it amounts to using a continuity tester to see there is
>> a connection versus how many ohms there are between the 2 points of
>> contact.  Both AC clamp-on meters and DC Hall effect meters measure by
>> conversion, not direct readings.  Magnetic field intensity decreases
>> exponentially by distance, and the huge space inside the fingers of the
>> clamp means the reading changes if you reposition the wire from the
>> center of the gap to closer to the wire, and it's never accurate,
>> anyway.
>> 
>> You and I may have AC and AC/DC clamp meters, but I suspect the OP does
>> not.  A good AC clamp meter at Home Depot costs $60 to $120.  A good DC
>> clamp meter greatly hikes the price to $500, and up.
>> 
>>> I try to keep a spare PSU in the house, but it's tough. 
>> 
>> I tried the same using a modular PSU, so I only need to connect enough
>> cables to the PSU as were needed for the particular build.  But
>> eventually it got used in the next build.  A $150+ PSU makes for an
>> expensive parts drawer.  For an emergency, I'll pay for overnight or
>> 2-day delivery rather than buy a PSU that may never get used.  However,
>> I have other computers to use, so I go with free delivery in 5 days.
>> 
> 
> I have an AC/DC clamp meter with Hall Probe technology that
> is every bit as good as your Harbor Freight multimeter, 

I don't buy much at Harbor Freight.  Mostly just focus on Pittsburgh
brand.  For multimeters, never bought one there.  Instead of Ames, I'd
rather spend the money on Klein at Home Depot, and the other brands at
Harbor aren't work even putting in my car's toolbox.

> Mine will measure 

Brand?  Model?  Price?

> That meter, is the most expensive meter in the house, at around $300
> or so. 

So, I wasn't far off in guessing $500, or more, for a clamp meter that
includes a Hall sensor.  Guess I'm looking for a couple extra features
as baseline that up the price.

You and I like good tools, and collect them like women collect shoes
(sorry, couldn't help using the sexist analogy).  I have oscilloscopes,
too, but I don't expect typical computer users to have many tools other
than a few hand tools they acquired for fixing doors and tables.

> You could make the measurement with a Harbor Freight meter too.
> But it would mean buying a 24 pin extension cable for ATX, cutting
> the +5VSB wire in two, and inserting the meter in-circuit. Which is
> why I don't suggest doing it that way. It interferes with circuit
> operation, and if the wire opens, the PC goes off.

That's why I figured the OP wouldn't be measuring the amp draw on 5VSB.
Really all he needs to check is there is 5VDC on the 5VSB line.  Even
the lowest grade PSUs should be able to provide enough amps for that.