CMOS battery replacement question (Packard Bell 386SX-II motherboard) \ VOGONS

CMOS battery replacement question (Packard Bell 386SX-II motherboard)

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First post, by Geforcefly

Posted on 2021-01-20, 04:32

Geforcefly Offline

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I've been reading up on various CMOS battery replacements, but I have a question: The board I'm working on had a 3.6v barrel battery that I removed before any damage could be done. There is an external battery connector that measures 5 volts when the power is on. Based on that, I would think that I'd need to use a 4AA battery holder with rechargeable batteries for safe operation (without modification). There are diodes around the area (shown in the attached picture), so perhaps maybe? Let me know what you think.

Reply 1 of 10, by Thermalwrong

Posted on 2021-01-20, 09:19

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I've got the same board I think, I just put a coin cell on the terminals like this. It seems to work, but if you're seeing 5v on there, I wonder how safe it is?

Reply 2 of 10, by maxtherabbit

Posted on 2021-01-20, 14:59

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Normal to see 5v on the ext battery header. It doesnt mean anything - there is a diode (or 2) protecting the battery from being charged by it

Reply 3 of 10, by douglar

Posted on 2021-01-20, 15:45

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I did my first battery replacement yesterday, also with a 386sx.

Photo Jan 20, 10 38 44 AM.jpg

Photo Jan 20, 10 38 58 AM.jpg

I soldered the minus pin to the motherboard and bridged one of the plus pins to the motherboard with a diode.
I used a little hot glue to stabilize the coin socket.
Diode caused the voltage to drop from 3.3V to 3.05v, but the motherboard seems to be OK with that.

Did I do that right?

Reply 4 of 10, by chrismeyer6

Posted on 2021-01-20, 16:05

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As long as the battery isn't getting the charging voltage and your bios settings are being stored you should be good to go. I'd also make sure to clean off more of that corrosion as it will continue to eat away at your motherboard.

Reply 5 of 10, by douglar

Posted on 2021-01-20, 17:06

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chrismeyer6 wrote on 2021-01-20, 16:05:

I'd also make sure to clean off more of that corrosion as it will continue to eat away at your motherboard.

I gave it a third scrubbing with vinegar and none of the green would come off on the swab. Should I try a different solvent?

Reply 6 of 10, by chrismeyer6

Posted on 2021-01-20, 18:01

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You can try some 99% isopropyl alcohol and a soft tooth brush and see if you can get anymore off and then give it a quick rinse with some distilled water

Reply 7 of 10, by douglar

Posted on 2021-01-20, 20:14

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chrismeyer6 wrote on 2021-01-20, 18:01:

You can try some 99% isopropyl alcohol and a soft tooth brush and see if you can get anymore off and then give it a quick rinse with some distilled water

That didn't make a dent in it either. I ended up using some "lime-a-way" cleaner that I use on hard water stains. That took off the deposits after a little scrubbing. I rinsed it well afterwards.

Reply 8 of 10, by chrismeyer6

Posted on 2021-01-20, 20:40

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Good I'm glad you found something that was able to work for you. Getting it as clean as possible allows for a nice long life for your parts.

Reply 9 of 10, by Geforcefly

Posted on 2021-01-21, 03:38

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Thanks for the feedback. I'll probably get a 3xAA battery holder and place it away from the board to eliminate any chance of battery corrosion causing issues.

Reply 10 of 10, by chrismeyer6

Posted on 2021-01-21, 03:56

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That's a good idea keep the batteries as far from the other components as possible.

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