CMOS Errors on boot

[jonathonoss]

I have an old IBM Thinkpad 770. It was dropped once several months ago, which smashed up the corner with the power button. Apart from having to start it with a long-nose pliers (because the power button broke off), I have had no trouble with it, until now.

The laptop sat for several weeks without a power connection, and yesterday when I plugged it in to start it, I got errors 173 and 163 in that order. 173 = "Bad CMOS/NVRAM checksum", and 163 = "CMOS error; Clock is not updating". It then promtps me to set the clock and then to cold boot the machine. However, I get the same errors on bootup (173, 163) -- no change. When it prompts me to set the clock, I notice that it kept the same time that I entered before the boot! Maybe the CMOS battery is good?!?

So then I tried entering into BIOS setup, as I read that saving your CMOS settings can fix CMOS checksum errors; however, it doesn't let me enter the BIOS setup! After several cold boots and setting of the clock (although each time it keeps the time from the prior boot, so the battery must be working), I decided to take out the CMOS battery and let it sit for about 15-30 minutes.

When I put the battery back in, I got errors 161 and 163. Error 161 = "CMOS configuration lost (battery has died)", Error 163 = "CMOS error; Clock is not updating". This time, the clock had reset, so I set it and did a cold boot. Then it was error free and it booted the O/S. I warm booted the machine a few times and I received no errors.

This morning I started the machine and now I have the same errors: 173 and 163. Removing the battery for extended periods does not work.

Is it the CMOS chip that's the problem?, if so can the CMOS chip be replaced? It doesn't seem to be the battery problem because it keeps time, right? Does the CMOS ever rely on AC power, or does it only rely on the battery no matter if the laptop is plugged in or not? Any suggestions?

Thanks,

Jon

 

[edfair]

Let it stay plugged in for a day or so and see if it will hold the date.
CMOS fed by the battery and battery fed by machine voltage so the battery will drain down. Ed Fair
unixstuff@juno.com
Any advice I give is my best judgement based on my interpretation of the facts you supply. Help increase my knowledge by providing some feedback, good or bad, on any advice I have given.

 

[dinosnake]

OK, to get into the BIOS of an IBM laptop you usually hold down the F1 key right after powering the computer up. It will not let you gain access to the BIOS from a reboot - only a cold, dead start from off to on.

It sounds like the backup battery is dead. The unit has 3 batteries - main power, standby power and backup power. The backup is responsible for maintaining the CMOS and the date/time. The Standby kicks in when you remove the Main to swap when dead for a new one. This is why when you turned the unit off for 15 minutes or so the clock kept running - my estimate is that the Standby battery had enough charge in it after you ran the unit for a while to keep the clock chip running when shut down. After a while it too ran out and you started back from the beginning.

I love IBM laptops and here is why:

ftp://ftp.pc.ibm.com/pub/pccbbs/mobiles/37l5152.pdf

This is the Hardware Maintenance Manual for the 770 series. Right on-line for you to download and look at.

Replace the backup battery and you'll probably be fine. Your mileage may vary...

 

[jonathonoss]

Thanks for your responses.

The CMOS battery was the problem. It was so easy to do a voltage test (which confirmed the dead battery) and replace the battery with one from another computer to see if there were no other problems, that it should probably be your first step in checking CMOS errors. Even though I didn't think it was the battery when the time was recalled on reboot, it still was a battery problem. I understand that the RTC/NVRAM must be getting power temporarily from another source to keep time temporarily.

Jon