On 6/3/2019 3:28 PM, VanguardLH wrote:
T. Ment wrote:

On Mon, 03 Jun 2019 17:00:42 +0100 (BST), rp wrote:

Replace the power supply.

It's a $20 special. I don't care about perfection.

That is way too cheap for a decent power supply. When I do a build,
most of the PSUs that I end up looking at are $80 at a minimum but
usually spend a lot more. However, I don't know what you got for
capacity (VA or watts) for your PSU, or its efficiency (less efficient =
more heat = more thermal stress = less capacity to internal components
since the A/C outlet isn't changing its voltage).

Figure on losing 5% capacity each year with a decent PSU. That's why I
buy PSUs that are much higher in capacity than the load they will
initially need to handle. For a 400W load, I'd get a 750W PSU because
in 8 years (what I like to build for longevity) the PSU will still be
more than enough at 66% of its initial capacity. The 5% is a rough
estimate of capacity reduction, but PSUs do wane over time. Cheapies
die off much quicker. The PSU supplies the life blood to the computer.
If you do the build, you are the hematologist for the computer.

How old is your $20 PSU?

Was it a pre-built computer or did you do your own build? The PSUs that
come in pre-builts are often minimal for the standard configuration by
the model (with the same PSU used within a family of models). They
don't overbuild since they're maximizing their profit margin.

The 5v disk connector may well come from another regulator. At
the very least measure the 5v at the motherboard multiconector
from the psu.

I won't buy another power supply if this one gets me by. My question is,
what tolerance is safe.

4.75V is the minimum. Less voltage means supplying more current to
handle the same load, and more current puts more thermal stress on the
supply components.

I'm curious as to why you say less voltage means supplying more current.
Doesn't that violate Ohm's law?

I = V / R

If V = 5.00 Volts and the load (resistance) R = say 10 Ohms then the
current I = 0.500 Amps.

If V = 4.75 Volts and the same load then I = 0.475 Amps.

Or is there some kind of perverse circuitry in computer power supplies
that make them work differently?

Charlie

snip