Optiplex 745 starts, then immediately stops

Question

This is not the same as previous similar discussions. New ideas?

Cold start. I push the power button, the pilot light comes on, the power light on the internal DVD drive comes on, the HDD starts to spin up. Then, in less than one second, it shuts off. Lights off, HDD spins down. Wait 3 or 4 seconds, and the cycle repeats. Again and again and again. If I let it do this for several minutes, it will suddenly decide to stay on. It boots correctly into Windows 7, and performs normally, all day.

It is not a heat problem. The machine is cold, and doesn't stay up long enough to generate any heat. It is not a Windows problem - it doesn't stay up long enough to start Windows. There are no error messages, ever. There are no strange noises. I have set the Power options to "Pressing power switch does nothing", so I don't think it is a sticky power switch. The BIOS battery was good, but I changed it anyway. Once running, HDD and DVD drives are good (I just created a system image and a recovery disk on those), the memory is good, and apparently the power supply is good. Ideas?

Bill

redxps630 · Answer

Could be stock psu is beginning to fail. Typical story I heard from user that his Dell power button appeared to be not working that well, that needed repeated pressing to turn on pc.  I replaced his psu and found the power button perfectly working.  Test your 745 using a verified working standard 24/4 pin psu to confirm.

redxps630 · Answer

Yes, that is a good plan.  What I meant is borrow the working psu from the other good 745, unplug the psu in question, use the borrowed psu to test the 745 motherboard.

Bill-J · Answer

I'm not anxious to buy a new PSU in hopes that it will work. But it would seem that another way to handle it would be to get a second, working, Optiplex 745 (I have one!), switch power supplies, and see if the problem follows the PSU to the working Optiplex. Sound good?

Bill

hankdutch · Answer

There is a 1,800 uF 6.3V electrolytic capacitor next to the PSU heatsink. Other 7XX models also affected.

bradthetechnut · Answer

@hankdutch​  You already posted this in another thread.  https://www.dell.com/community/en/conversations/optiplex-desktops/optiplex-760-shut-down-randomly-on-booting/647f9059f4ccf8a8de19809f

Optiplex Desktops

Optiplex 745 starts, then immediately stops

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