Re: HP-21 displays all zeroes Message #3 Posted by Randy on 23 Jan 2012, 9:18 p.m., in response to message #1 by Barry Smith
The article does not apply to the HP21 as it has no external ram.
Based on what happened, the problem is either a bad battery or bad contact with said battery. If the battery has been rebuilt, make sure the cells are connected with a welded strap, do not rely on the spring to do the job - as even a small amount of corrosion will cause problems. When you have a bad battery or bad contact, connecting the calculator to the HP charger can and usually results in catastrophic failure of the ACT (arithmetic, control, timing) IC. In other models of the 20 series, other components can be damaged as well.
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