[plug] OT: hardware troubleshooting

Andrew Cooks acooks at gmail.com
Sun Jun 14 01:25:55 UTC 2015

On Sat, Jun 13, 2015 at 5:22 PM, Andrew Cooks <acooks at gmail.com> wrote:

> Hi Pluggers
> I've got a problem with a box not powering up and I hope someone can help
> me figure it out.

Thanks to Kevin, Linda and Garry.

I have discovered the magic startup conditions for this box:
Step 1. Set the motherboard to remain powered off after a power failure.
This is critical. If the board starts immediately, reset the firmware
Step 2. Restore power to PSU, then wait 5 seconds. Note PSU fan starts in
low speed mode and motherboard LEDs turn on.
Step 3. Press and hold power button, closing the switch for 1 second.

My major mistake was that I failed to test things properly after changing
the firmware settings to power up the system automatically when power is
restored (like after a power failure).

The behaviour described above suggests to me that the board overloads the
PSU if it starts immediately and that the few seconds between PSU power on
and MB power on is enough to allow things to settle. Perhaps one of the EEs
on the list can tell me whether it's capacitors charging or little MCUs
involved with the power regulation on the MB or in the PSU that needs time
to settle?

Two more curious things:
1. It doesn't make any difference whether there are lots of devices
connected, or whether the MB only has a CPU plugged in (no RAM, GFX, fans,
or spinning rust connected).
2. Why would the MB power switch need to be closed for a few hundred
milliseconds? (A quick press and release results in it turning off again).


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