BIOS settings lost after unplugging

aisle9 · September 4, 2017

Before you reply, "Change the CMOS battery," read on. This is regarding a Dell Vostro 200 prebuilt with a DG33M03 motherboard, Core 2 Quad Q6600, 4GB of RAM (4x1GB), 250GB WD Blue hard drive, and at the time of the failure, a Radeon HD 4870. Oh, and an Apevia 500W PSU. Probably garbage-tier, but it's what I had lying around, and I figured my whole system draw would be within its bounds.

So here's what happened: I had the 4870 hooked up and was stressing the CPU and GPU to see just how stable the system was. This is a Vostro I've had for a while, but the 4870 is new and I wanted to see what it could do paired with the Q6600. After about 15 minutes of the test, the system just shut down abruptly. Some quick diagnosis showed that, yep, the PSU was shot. After disconnecting it, it wouldn't power up on the paper clip test. I switched it out with a different PSU I had lying around, disconnected everything but the RAM, and...no display. Popped the 4870 back in as a display adapter, nothing. The board was giving me a single beep, which is Vostro-ese for "motherboard problem, send back to Dell".

Here's where it gets weird. After unplugging it, resetting CMOS, installing a new Apevia PSU (again, it's what I have lying around) and reseating the RAM, I was able to bring the system back to life. After getting into Windows, I powered down and unplugged the PSU to install a lower-draw GTX 260, the HP OEM Fisker2 variant that only uses a single 6-pin, then booted back up to see that my CMOS had been reset. Huh, ok. Maybe the CMOS battery was dead. I powered back down and swapped it out with one of the many CR2032 cells I've harvested from decommissioned computers in the past. Plugged it in, re-entered the BIOS settings and got into Windows. After a couple of boot cycles, the BIOS settings were holding up. Problem solved, right?

I unplugged the system again shortly thereafter to swap out the CPU cooler aaaaaaaand the CMOS reset again. Figuring I had another dead battery, I replaced it with one fresh out of the blister pack. A few boot cycles and the settings held, then when I unplugged again to swap out the rear exhaust fan with a quieter one, the settings once again were lost and I had to reset.

What's going on? I've seen bad PSUs damage a motherboard before, but never seen CMOS settings that refused to save. The battery is definitely seated correctly, and the new battery should be fully charged. Is it possible that the PSU failure caused damage to the CMOS battery connections somehow, or is there something I'm missing here that could be the cause of the whole problem?

Lord Nicoll · September 4, 2017

6 minutes ago, aisle9 said:

snip-

I'd say the PSU took out the battery subsystem, maybe something for monitoring it or there abouts, or a short on the board is draining the battery fast, maybe putting voltage through, without a DMM and 30 minutes probing around I can't say for sure.

Hiitchy · September 4, 2017

It sounds like a short where some part of the system is draining the battery when the power supply is off... Do you have a battery tester or multimeter lying around where you can check the charge level of the battery? That's really strange.