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CMOS error on Commodore 386 with replaced battery

T

tonata

Experienced Member
Joined
Sep 11, 2019
Messages
190
Location
France
Hi,

I have replaced the internal barrel battery of my Commodore 386 with a new coin 3V battery, but I still get CMOS error and the computer can not keep its settings. I am using a 3V battery which actually goes to 3.6V when measured with the computer powered off. It is 3.7 when the computer is on.
There is one jumper saying int/ext so I have set it to int. The two pins are really connected.
I do not understand why it is still not working.
The + and - are correct on the battery.

Is it possible that the CMOS RAM is not working? Does this ever happen? Can it be replaced?
 
You can't use a non-rechargeable battery to replace a rechargeable battery without using a diode. If you just slapped a CR2032 across the terminals where the old battery used to be, it's going to eventually rupture or explode.

In any case, a coin cell battery is too low of a voltage. You need 3.6v, not 3v. Either use a more modern NiMH barrel battery, or 3 x NiMH AAA batteries in series in a battery holder external to the motherboard.
 
My son once forgot to take his cell phone out of his trousers and my wife put it in the washing machine. The battery survived. I soldered to wires to it and now it serves in one of my C= 286 machines. Two advantages: 1) its capacity is bigger than the original Varta and 2): not a chance that it will leak on the board; I used velcro tape to attach it to the case.
 
Ruud, what was the original battery? I think it was not rechargeable.
The battery I have placed has a charge of 3.6 V (even if it says 3V), so it should be enough.
 
tonata said:
Ruud, what was the original battery? I think it was not rechargeable.
The battery I have placed has a charge of 3.6 V (even if it says 3V), so it should be enough.
Click to expand...

CR type coin batteries are NOT rechargeable. The reason you're getting 3.6v is because the motherboard is forcibly overcharging the battery. CR type coin batteries nominal voltage is 3.0 volts, not 3.6 volts. You need to remove that battery before it ruptures or explodes.

Motherboards from the 286-Pentium era used NiCD barrel batteries, which are actually 3 button cell batteries of 1.2v each to make up the 3.6v.
 
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