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Re: Computer turns on and then just dies

From Paul <nospam@needed.invalid>
Newsgroups alt.comp.hardware, alt.comp.hardware.pc-homebuilt
Subject Re: Computer turns on and then just dies
Date 2024-11-21 15:58 -0500
Organization A noiseless patient Spider
Message-ID <vho6to$q2jk$1@dont-email.me> (permalink)
References <lq91ciFjetU1@mid.individual.net>

Cross-posted to 2 groups.

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On Thu, 11/21/2024 10:19 AM, s|b wrote:
> I've got a computer I haven't used for some time. I took out a hdd (D:)
> and left it alone. I'm trying to get it to work again, but it just dies
> on me. I've reinstalled the missing hdd and replaced the BIOS battery.
> 
> When I flip the switch of the power supply the standby power led on the
> motherboard (ASUS F1A75) turns on, stays on for a bit and then dies. If
> I then try again, nothing happens. I have to turn off the power switch
> (power supply), leave it off and then try again. I can get in the BIOS
> shortly (all fans are blowing) and then power's gone again.
> 
> I checked all cables and they should be fine. What could be causing this
> and how to solve?
> 

"flip the switch... standby power led on ASUS F1A75... stays on for a bit and then dies"

The power supply consists of two halves.

The supervisor power makes +5VSB.
On an Asus motherboard, the +5VSB LED is tied right to that rail.
When you see the Asus LED go OFF, it means the +5VSB supply is OFF.

It has nothing to do with the main SMPS block, which makes 3.3/5/12/-12

In the situation where you got the BIOS to respond, it means
the +5VSB circuit was running, and main SMPS was running,
then the +5VSB fails and the +5VSB "enables" the main SMPS.
Both of them go off. The +5VSB is the "boss of the machine".

Your first observation then, is indicative of the problem.

1) Open PSU casing, check for cobwebs or hair, or some component
   has fallen off its heatsink. Be careful in there, as it's HVDC
   in part of the circuit. 300-500VDC could be on the main cap.

   Also examine for leaking caps (brown stain on top of caps where the
   cap has "K" or "X" seams"). On a failed Antec (ChannelWell CWT)
   here, it was four capacitors on the main supply that were leaking.
   I also had an Antec where the Antec was a spare, and two years
   after I bought it, I went to use it, and it had leaking caps
   just sitting in storage. The Bad Cap Era was not stress related,
   it was bad chemistry (wrong pH) inside the electrolytic cap.

2) Use a clamp-on ammeter, to monitor the +5VSB wire on the main cable.
   On modern sheathed cabling, we can no longer conveniently do this test!
   The PSU may have a 3 ampere limit. +5VSB at 1 amp might be a typical value
   for a load. Charging your iPhone off USB may draw up to 2 amps, which
   would be very close to the limit for a +5VSB. when the fan stops spinning
   on a PSU which normally spins the fan at all times, and you were charging
   your iPhone, it means the +5VSB runs without cooling. I would recommend
   people NOT charge junk off the PC port -- it might extend the life of the
   +5VSB block.

Here is a reference circuit. They don't build PSUs this way any more.
This diagram then, is just to understand the block level concepts.

http://www.pavouk.org/hw/en_atxps.html

The +5VSB block is in the lower left corner. This one happens to be a
linear regulator with fairly low output current capability. Modern
supplies use an SMPS with MOSFETs for that block, and hopefully,
with higher efficiency. The SMPS doesn't kick out the heat
that the item in the diagram does. You can get linear regulators at
the 3 ampere level, so it is possible to build that circuit as a linear,
but it could really throw out a lot of heat if charging an iPhone.
That's why today, it's a tiny SMPS in the lower left corner.

The top middle of the diagram, has two power transistors switching the primary
winding of the shared transformer. The secondary side has rectifier diodes,
and LC filtering to make low-ripple DC on the output. That was back when the
main SMPS was a single circuit. The evolution of the main SMPS into
two SMPS boards is irrelevant to your debug today.

At one time, some of the AthlonXP designs (before your AMD was invented),
they used +5V @ 13A for the CPU supply. This changed to +12V at many more
amps, from the PSU. The PSU designs of today, have HUGE +12V ratings,
suited to running CPUs and video cards. One of the consequences of that,
is the modern PSUs don't expect big +5V loads any more. If selecting
a supply to run a dual socket AthlonXP board, none of the modern supplies
would be suitable. There were a few PSUs back in those days, that could
do +5V @ 40A, whereas the ones today can do +5V @ 20A, and that's not
enough to run my AthlonXP sample build here.

Your motherboard is modern enough, that the PSUs are mostly intended
for it, so you can buy most anything. Beware though, that some of the
supplies have the connector for the RTX4090 GPU and they don't have
quite the same selection of PCIe 2x3 and 2x4 supply connectors.

PSUs can be expensive. I picked up a "mid value" supply at Best Buy
(as the computer store had a poor selection) and that supply was
$150.00 CDN. The last two builds used a 750W (in the low power PC)
and a 650W (in the high power PC). I'm just slapping in whatever
is sitting on a shelf :-) Since the individual builds happen without
coordinating where best to use the supplies, sometimes I end up
with illogical choices like that. The 650W one has maybe 350W of load
or so. The +3.3V and the +5V are likely 10 amps or less (out of 20 amps).
The 3.3V and 5V have a "combined power" - on a Seasonic the combined power
is 100W. On some other brands the combined power is 130W. My daily driver
PC has the Seasonic in it SS620GB has combined power of 130W for the
+3.3V and +5V board, so I must have been checking which Seasonic
I was buying on that day. This is why you have to sort your Seasonic
into piles, in terms of rating.

I try to keep a spare PSU in the house, but it's tough. I don't
have a spare right now. Everything is in computer cases. And I don't
particularly want to go out and buy another $150.00 supply right now.

Sometimes, there are clearance sales. When Enermax left the country
(could not get reliable warranty service from Canadian warranty companies),
some of their supplies went for a lower price. This offers a chance
to find supplies at a discount. "Keeping a spare" then, represents
an open order, to be filled by a supply which is on sale. So really,
my spare is a measure of "how cheap I am" :-) By buying a spare before
you need it, you can shop for bargains. So what if it doesn't have
a warranty.

   Paul

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Thread

Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-21 16:19 +0100
  Re: Computer turns on and then just dies Marco Moock <mm+solani@dorfdsl.de> - 2024-11-21 16:28 +0100
    Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-21 17:07 +0100
      Re: Computer turns on and then just dies "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2024-11-22 00:18 +0800
        Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-21 17:57 +0100
          Re: Computer turns on and then just dies "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2024-11-22 11:42 +0800
            Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-22 19:47 +0100
              Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-22 20:34 -0500
          Re: Computer turns on and then just dies "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2024-11-22 11:47 +0800
            Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-22 19:48 +0100
              Re: Computer turns on and then just dies "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2024-11-23 12:12 +0800
          Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-23 15:18 -0600
  Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-21 16:35 +0100
    Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-21 12:43 -0600
      Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-22 19:56 +0100
        Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-22 17:32 -0600
  Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-21 12:22 -0600
    Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-22 20:01 +0100
      Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-22 18:03 -0600
  Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-21 15:58 -0500
    Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-21 23:28 -0600
      Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-22 07:24 -0500
        Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-22 10:20 -0600
    Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-23 12:09 +0100
      Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-23 07:07 -0500
        Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-24 17:12 +0100
          Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-24 15:21 -0500
            Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-25 14:58 +0100
              Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-25 17:33 -0500
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-26 18:44 +0100
                Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-26 16:31 -0600
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-27 15:38 +0100
                Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-26 21:04 -0500
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-27 16:01 +0100
                Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-27 10:19 -0500
      Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-23 14:28 -0600
        Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-24 17:10 +0100
          Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-24 15:27 -0500
            Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-25 15:08 +0100
        Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-25 14:38 +0100
          Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-26 16:37 -0600
            Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-27 16:05 +0100
  Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-24 16:51 +0100
    Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-24 16:03 -0500
      Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-25 15:03 +0100
        Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-25 18:09 -0500
          Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-30 12:28 +0100
    Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-27 15:45 +0100
  Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-28 17:17 +0100
    Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-28 11:07 -0600
      Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-28 19:30 -0500
        Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-28 19:34 -0600
          Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-29 05:21 -0500
            Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-29 11:35 -0600
        Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-29 13:49 +0100
          Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-29 17:11 +0100
            Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-29 15:01 -0500
              Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-29 21:46 -0600
              Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-30 12:21 +0100
                Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-30 09:15 -0600
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-30 17:16 +0100
                Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-30 17:40 -0500
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-02 11:43 +0100
                Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-12-02 14:15 -0600
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-02 21:19 +0100
                Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-12-01 08:26 -0600
                Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-12-01 13:23 -0500
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-02 11:40 +0100
                Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-12-02 14:06 -0600
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-02 21:30 +0100
                Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-11-30 11:31 -0500
                Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-11-30 12:22 -0600
      Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-11-29 12:46 +0100
  Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-04 17:41 +0100
    Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-12-04 14:14 -0600
      Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-12-04 18:28 -0500
        Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-12-05 09:30 -0600
          Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-12-05 11:11 -0500
      Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-06 17:43 +0100
        Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-06 17:45 +0100
          Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-12-06 16:46 -0600
            Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-07 14:11 +0100
              Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-12-07 09:46 -0600
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-07 17:02 +0100
                Re: Computer turns on and then just dies VanguardLH <V@nguard.LH> - 2024-12-07 11:40 -0600
                Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-09 15:54 +0100
        Re: Computer turns on and then just dies Paul <nospam@needed.invalid> - 2024-12-06 20:43 -0500
          Re: Computer turns on and then just dies "s|b" <me@privacy.invalid> - 2024-12-07 15:27 +0100

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