Electronics > Repair

unusual computer motherboard issue.

(1/3) > >>

I have a NLA, unsupported, custom industrial motherboard with a bit of an odd issue. I'm not really sure where to start diagnosing it. it is a MX280NI.

it's set in the bios to "on AC loss", to power on... so you can use the main AC power switch to power on and off the system.  For some reason, after 4 years, it has now stopped doing this. for whatever reason it has randomly decided to not power on when the power switch is applied. the power comes on, the computer appears to start the BIOS to start the POST, does the POST beep and it immediately powers off. if i jumper the power switch header, it powers on and operates normally.

I've reset the BIOS defaults and set the appropriate option to have it power on.. it just doesn't do it. Motherboard has new BIOS battery. but it still wouldn't power on like it's supposed to. I decided that I would program a microcontroller to wait a few seconds (for the computer to fail it's initial poweron) and then "press" the power button. this got it going in the interim.

this worked for a while... then just as randomly as it stopped powering on... it started up on it's own again just like its supposed to. (problem was, my microcontroller would then power off the computer) So i disabled the microcontroller, powered on the board, had it boot up, and everything was good for about 30-45 minutes... then it just blanked out and shut off. jumpering the power header powered it back on again.

the computer powers on normally by itself about 20% of the time. so i've managed to confirm that when the computer powers itself on, the computer will eventually shut off after about half an hour to an hour of running. when the power button is actuated (or my "defibrillator" microcontroller turns it on) it will stay on an indefinite amount of time. thermals are good so it's not powering off due to anything i can tell, other than just giving up and not wanting to stay on any longer.

so it seems whatever the bios is using to turn on and keep on the computer when the on AC restore setting is set to on....and whatever the power switch header connection are using to turn on and keep on the computer...are 2 different systems?

short of disabling the on AC restore function and keeping my "power on defibrillator" microcontroller as the primary means of powering on the system...what could possibly be the issue? I'd like a not so hackey poweron but if that's what it is going to take that's what it is then.

does suspicion about the 2 separate systems hold any truth?

I think you need a new power supply.  PC power supplies are getting more complicated, with microcontrollers in them to manage power on/off and self-test.  And, you can get all sorts of flaky results if the standby supply is bad.

this motherboard simply takes 12v in and has DC-DC converters in it to create it's own rails. if a rail was going funky, I'd think it would act more inconsistent in how it behaves.

as it stands, manually powering it on with the power button, the motherboard operates 100% of the time.

having the PC auto power on with the bios setting "on AC loss" set to ON... (and when it does power on) fails 100% of the time. (eventually)

it's weird.

This one? https://www.bcmcom.com/bcm_product_MX280NI.html

The chipset datasheet is here: https://datasheet.octopart.com/CG82NM10-S-LGXX-Intel-datasheet-76215416.pdf
Section 5.14 contains the details of this functionality, specifically

In particular: "Pressing the PWRBTN# Signal for more than 4 seconds to cause a Power Button
Override event."...which turns the system (soft-)off immediately.

--- Quote ---the power comes on, the computer appears to start the BIOS to start the POST, does the POST beep and it immediately powers off.
--- End quote ---
Does it take almost exactly 4 seconds when it decides to do that? If so, I suspect what's happening is that the power button is "stuck down", so that when A/C power is restored, the chipset correctly powers up based on the configuration (see the text about "AFTER_G3" in the datasheet) and begins to boot, but then due to the stuck power button, goes into soft-off after 4s.

Worth nothing to mention i have seen similar symptoms with PSU having aged bad caps with very high ripple when warmed up...

They look and behave normal cold and start the funky dance when warm



[0] Message Index

[#] Next page

There was an error while thanking
Go to full version