On 02/21/2018 04:46 PM, Paul wrote:



snipped for brevity


My tester gives an over-all fault (red) for those supplies but all
other green lights are lit up but one.


Now that I have the machine all put back together and working I don't
think I'll fool with it anymore, but one of these days when I get a
*

My P2B-S (year 2000???) has a voltage monitor input for -5V, but
no circuitry on the motherboard uses -5V. The two RS232 chips use
-12V for the bipolar RS232 output swing. Even my P4C800-E Deluxe
(a P4 mobo) didn't use a Maxim "pumped" RS232 and the TI 75232
chip on that one continued to use -12V. That's about the only
reason to still have -12V. You can use -12V for op amp circuits,
or maybe for a little 2W power amp for passive speakers, but other
than that, there aren't a lot of excuses for -12V. And the -5V
back in the day, was used for digital chips. And all those chips
stopped using -5V. For maybe a year or two, you could build a
design purely out of +5V circuitry, but then the industry moved
on and new voltage requirements were introduced. Today, a Southbridge
could have as many as five rails on it (with many of the voltages
made by circuits on the motherboard). Even a NIC is dual rail, with
maybe 3.3V for digital I/O signals, but 1.8V or lower to power
the core circuits inside the chip.

Core logic today can run off 1.0V. They even make op amps that
run off voltages like that. I don't expect they'll go too much
lower. The 200W video card you own, the core of that runs at
around 1.0V. And the voltage regulator has to provide 200A
of current, and the copper planes in the video card have to
be able to withstand a 200A flow.

*******

You might notice that one pin on the ATX PSU, has two wires.
That's for remote sense of 3.3V output. That remote sense leads
to tighter regulation on the 3.3V output. To make the ATX PSU
supply 1.0V to the motherboard say, you'd need to run the
remote sense right to the load, to do a good job. This is one
reason that power supplies will not be making voltages lower
than the 3.3V they make today. Tolerances. And the cabling
that results from doing it that way, would be quite inconvenient.

Â*Â* Paul




And then of course there are those old Dell non-standard ATX supplies.

I suppose I could probably get rid of the few I have left.


Anyway as always, I think you for your extreme knowledge .



BTW: I still do computer repair work and this young woman brought over a
machine she uses for video editing. It quit on her when her boyfriend
who built it was out of town.


The problem was simply that the power wire fell off the SSD.


It had a relatively small case and the PSU wires were long and bulky.

I had to re-route and tie down the cables ,



The last machine I built for myself, the one I'm using now has a mini
motherboard and a huge case (22" high)