System turns on by itself.
Posted on 2014-01-23
I’m curious as to whether anyone can provide some insight as to why a motherboard would draw power 25 minutes after the power switch was pressed. Please read on for details.
I was brought a Compaq desktop PC to test after the customer said it was blue screening. He did not document the errors so I have no idea of the cause.
I connected the system to a surge protected AC outlet and pressed the on button and absolutely nothing happened. I checked the cables and ensured that the green power LED on the PSU was on. It was and everything was connected correctly.
I swapped the PSU but the result was the same, no power. I swapped out the RAM, cleared the CMOS and replaced the CMOS battery. Same result.
I removed the mainboard, placed it on my test bench and connected all the necessary cables. Still no joy. I removed the power jumper from the front panel header and made myself a coffee. I then called the customer to give him the bad news.
After about 15 minutes into the telephone conversation the system powered on. But I hadn’t touched the thing for 25 minutes and the power jumper was not connected! How can this happen?
I have never seen this happen before and I have no idea why or how it happened so if anyone has any ideas I would love to hear (read) them.