hp-12c from HP.com arrives with dead batteries



#6

I did not feel like I should buy more of the hp-15C LEs so I decided to fulfill my long desire of owning a 12C. So I ordered an usual (not AE) model from hp.com and it has arrived today.
Only thing was it did not turn on out of the box. I replaced batteries and the machine is back to life.
I checked the cell voltage and they were 2.3 and 2.6 volts without any load.
Firmware date is 2008.6.28 and serial # is 4CY1150D5T.

I am not sure how long this was on the shelf, but I am wondering what is my odds of having received a unit with internal short.


#7

The off state current is only a few microamps. That should take many years to discharge the 2032 cells if the calculator shut down properly. You might indeed have unit with a bad CPU or other components that allow for current leakage. However it could be just one bad cell. Since the cells are in parallel a single bad will will drain the other good cell.

Since you're able to measure the cell voltage, you likely have a DMM and that can likely measure current. Put the current meter in series with 3 volts powering the calculator. (2 AA batteries in a holder is easy to find if you don't have an external DC supply.) You should measure around 20ma when running a tight program loop, around .05 ma (IIRC) when on and idle and at most .005 ma when off.


#8

Since the batteries are in parallel, do you simply connect the power supply with 3 vdc to any one of the two battery terminals for testing ?


#9

Yes.

#10

Katie
Thank you very much for your advice. I measured these current levels and all fall in the range that you have identified. (except for the off current.. My RadioShack DMM can't detect micro amps) Maybe it was a bad cell. I feel much better now.


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