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X220: Computer won't boot after momentary CMOS battery disconnect

X200/X201/X220 (including equivalent tablet models) and X300/X301 Series
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WormMan
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Location: Copenhagen, Denmark

X220: Computer won't boot after momentary CMOS battery disconnect

#1 Post by WormMan » Sun Jan 23, 2022 4:43 pm

Here is a recurring phenomenon I have observed both times I have de-assembled my two X220 to replace the thermal paste and the thermal mat. This requires the CMOS battery to be disconnected for a moment. Both times, after putting the machines back together it won't boot with the regular battery pack plugged in and I need to let it sit for a few hours. Then it will only boot with the regular battery unplugged. The first machine started acting normally after that and I hope this one will also.

1. Is this a sign that I need to replace my CMOS battery?
2. Why can't I boot with the regular battery-pack plugged in, but only with the battery-pack unplugged?
3. Why does the computer need to sit for 1-2 hours after re-assembly before I can boot? (This happened to me twice so there is some kind of logic to it, I suppose).

Clearly there's something about the hardware/battery I have yet to understand, I would be very thankful if anyone could take me to school on the topic.
Best regards, WormMan

WormMan
Posts: 4
Joined: Sun Jan 23, 2022 4:31 pm
Location: Copenhagen, Denmark

Re: X220: Computer won't boot after momentary CMOS battery disconnect

#2 Post by WormMan » Sun Jan 23, 2022 4:51 pm

I should add I had a look at the Hardware Maintenance Manual for X220 without seeing anything related to these symptoms. A link or something where I might read up upon these aspects of the machine could bring me a long way.

RealBlackStuff
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Re: X220: Computer won't boot after momentary CMOS battery disconnect

#3 Post by RealBlackStuff » Mon Jan 24, 2022 1:05 am

There is absolutely NO reason to disconnect/remove the CMOS when you replace the thermal paste.
By now those CMOS batteries are about 10 years old, time to replace them.
For a cheap how-to see here: viewtopic.php?p=863727#p863727
(The X220 needs CR2032.)
Lovely day for a Guinness! (The Real Black Stuff)
IBM: T23 (XP/SP3) - Lenovo: X240, X250, T440p, M900 Tiny (all with W7/SP1)

WormMan
Posts: 4
Joined: Sun Jan 23, 2022 4:31 pm
Location: Copenhagen, Denmark

Re: X220: Computer won't boot after momentary CMOS battery disconnect

#4 Post by WormMan » Mon Jan 24, 2022 11:28 am

Hey, thanks a lot for responding RealBlackStuff.
RealBlackStuff wrote:
Mon Jan 24, 2022 1:05 am
There is absolutely NO reason to disconnect/remove the CMOS when you replace the thermal paste.
You're right. I just got into the habit of doing it.
RealBlackStuff wrote:
Mon Jan 24, 2022 1:05 am
By now those CMOS batteries are about 10 years old, time to replace them.
What function does the CMOS battery have in booting? What is the possible explanation for this situation where the machine needs to sit for a while before it can boot?

I'll replace them for sure. I'd just really like to learn more than the habit of replacing the CMOS battery from this.

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Re: X220: Computer won't boot after momentary CMOS battery disconnect

#5 Post by RealBlackStuff » Mon Jan 24, 2022 11:47 am

CMOS batteries keep the BIOS-settings 'alive', such as date/time, boot-drive preference, too many details to just list here. (look in the BIOS to get an idea).
If CMOS is not working, booting (and other items) will be slowed down, because so much needs to be recalculated from 'scratch'.
Lovely day for a Guinness! (The Real Black Stuff)
IBM: T23 (XP/SP3) - Lenovo: X240, X250, T440p, M900 Tiny (all with W7/SP1)

WormMan
Posts: 4
Joined: Sun Jan 23, 2022 4:31 pm
Location: Copenhagen, Denmark

Re: X220: Computer won't boot after momentary CMOS battery disconnect

#6 Post by WormMan » Tue Jan 25, 2022 12:00 pm

OK. I get it. If anybody else searches for X220 boot problems after disassemble I hope they'll find this post. Thanks RBS for providing some background.

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