CMOS error after changing battery on IBM PS/2 Model 76i \ VOGONS

CMOS error after changing battery on IBM PS/2 Model 76i

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First post, by jsp

Posted on 2021-08-05, 20:25

jsp Offline

Rank Newbie

Rank: Newbie
Posts: 31
Joined: 2018-06-29, 10:34

Hi,

I am trying to bring back to life an IBM PS/2 I got from ebay some years ago. It wasn't booting or displaying any output, and that turned out to be a bad power supply. After replacing it I am now facing a new challenge. The computer complains about the system configuration and time/date not set, typical symptoms of a dead battery. In the case of this IBM model, the battery seems to be located on the MCA riser (https://ardent-tool.com/76-77/7677_Lacuna.html#Lacuna_Riser) which seems to me a bit weird, but knowing IBM nothing can really surprise me anymore.

I changed the battery for a new one(despite my meter reading 3v on it) and after running the reference disk and setting the time, every time I power the computer off I get the same error. This wouldn't be such a pain if I didn't have to run the reference disk every time this happens, which is really time consuming.

I am a bit at a loss here, and would like to hear your ideas. Thanks in advance!

Reply 1 of 2, by jsp

Posted on 2021-08-11, 16:50

jsp Offline

Rank Newbie

Rank: Newbie
Posts: 31
Joined: 2018-06-29, 10:34

So, I have been looking at this issue. The new battery is perfectly valid, providing 3.28v that I have checked make their way all they way to the RTC Dallas DS1585S IC (pin 23, Vbat). Still, every time I switch off the computer (still plugged to the wall, but switched off) and reboot I will always get the two typical messages of a dead battery:
- System configuration error
- Time and date not set

I guess my question for people knowledgeable of the IBM PS/2 is if what I'm seeing points towards a dead DS1585S. Note that if I don't switch off the computer, I can reboot without issues or error messages so somehow the IC is doing its job until the time comes to get power from the battery.

Thanks for any tips or help

Reply 2 of 2, by jsp

Posted on 2021-09-01, 08:17

jsp Offline

Rank Newbie

Rank: Newbie
Posts: 31
Joined: 2018-06-29, 10:34

Well, after a lot of reading and digging from old posts in this forum I determined that the most likely cause of this behavior was a bad DS1585S. So I checked online and found pretty cheapo spares in AliExpress. I pulled the trigger, the risk/benefit tradeoff was just too good to pass.

I replaced the original DS1585S with the one from China. The process is not straightforward, the main problem being that the RAM sockets are mm away from the IC and are made of plastic, so you need to be extra carefull with applying heat in the area. For desoldering, I just applied some hot air using my heat gun. Took 30sec to come off without any damage to the board.

Soldering the replacement was a bit trickier, again because of the lack of space. The heatgun didn't make it for me. I ended up resorting to my small ts80p soldering iron to do the job. It took a couple of attempts until all the pads were correctly soldered. On the first attempt, some pads were not making good contact and the machine wouldn't boot at all. Flux always helps on these tasks, try to use the good stuff to avoid leaving any residues. The RAM sockets are 90% ok, some decoloring but no physical damage.

After being able to boot the machine again, I set the date and the configuration using the reference disk. I powered the machine off and on and .... it was freaking working!!! So it was a dead DS1585S after all.

I hope this story helps others users in diagnosing issues with the IBM PS/2 machines.

Cheers!

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