Replacing the battery on a 486 - some issues \ VOGONS

Replacing the battery on a 486 - some issues

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First post, by Thraka

Posted on 2015-05-16, 03:57

Thraka Offline

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I've tried attaching a coin battery with holder through a CD audio cable on to the external battery header but it doesn't seem to be working correctly.

My motherboard: http://museum.ttrk.ee/th99/m/A-B/33179.htm

It says JP1 is external battery, but it also lists it as a jumperable area.

JP1

1Battery type select internal  
2pins 2 & 3 closed  
3  
4Battery type select external  
5Closed  
6   
7CMOS memory clear  
8pins 3 & 4 closed

What confuses me is that there are only 3 pins, pin 2 is missing. So it looks like this: |0||

There is a place for where the barrel battery would have gone but the soldier looks brand new and perfect, as if there never was one.

My cable looks like this: +00- only two pins being used. Should I be doing this instead? +0-- But that seems like it would be bad because it would be triggering the clear the CMOS. At least I assume it would. Was pin 2 removed because the thing didn't come with a barrel battery or something? Very odd.

Reply 1 of 5, by firage

Posted on 2015-05-16, 04:22

firage Offline

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Location: Finland

The missing pin is there to key the battery connector. On my board the external battery connects +/Missing pin/NC/-

My big-red-switch 486

Reply 2 of 5, by Thraka

Posted on 2015-05-16, 05:20

Thraka Offline

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That's what I figured. So I have the same setup, +/missing/nothing/- but with it connected I had a CMOS error a few hours after being powered off.

I'm getting 2.9 volts out of the battery, seems like it should be enough.

Reply 3 of 5, by Maeslin

Posted on 2015-05-16, 15:14

Maeslin Offline

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That's actually most likely dead for a button cell. No-load voltage for a new one is ~3.2-3.4V

Best way to check is voltage under load, with a 100Ohm resistor hooked to the battery while measuring.

Reply 4 of 5, by Billyray520

Posted on 2015-05-17, 00:42

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On my 386 board, which I switched from a soldered in barrel battery to a coin cell (CR2032) I used 2 cells in series (giving me 6v.) I also had the problem where after a few hours I would still lose the CMOS. Turned out I had to ground the negative lead to the case. Then everything worked perfectly.

Retro stuff owned since new

386 20Mhz 2MB DOS 3.3/PC-MOS 4.0
AMD 386 40Mhz 32MB Win 3.11 DOS 5.0
486DX-2 66Mhz 128MB Win 95b
PIII 450Mhz 768MB Win 98SE
PIV 2Ghz 2GB Win XP/Ubuntu 10

Reply 5 of 5, by Thraka

Posted on 2015-05-17, 08:36

Thraka Offline

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I checked the negative pin with a continuity test to the negative soldier point on the barrel battery and they connected. Don't know if that makes a diff.. 😀 However, I posted another thing about my floppies not being recognized so I may just have to junk the board.. 🙁

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