HP 11C suddenly won't turn on

[Antonio Petri (UK)]

I have an HP 11C that I use very rarely. I was doing a simple calculation and the display suddenly started flashing; The calculator became unresponsive and I had to take the batteries out to turn it off. When I put back the batteries the only thing that the calculator did was to display the message "Pr Error", and it was still unresponsive at any key press, including the "on" key. I then removed the batteries again and waited a few minutes before to put them back, and the result is now that the calculator doesn't even display the "Pr Error" message and it doesn't turn on at all. The batteries are ok as I have tested them on my 15C.
I wonder whether what this problem is and most importantly, whether I can get my 11C working again.

Antonio

[uhmgawa]

Quote:

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I have an HP 11C that I use very rarely. I was doing a simple calculation and the display suddenly started flashing; The calculator became unresponsive and I had to take the batteries out to turn it off. When I put back the batteries the only thing that the calculator did was to display the message "Pr Error", and it was still unresponsive at any key press, including the "on" key. I then removed the batteries again and waited a few minutes before to put them back, and the result is now that the calculator doesn't even display the "Pr Error" message and it doesn't turn on at all. The batteries are ok as I have tested them on my 15C.
I wonder whether what this problem is and most importantly, whether I can get my 11C working again.

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Does the "Pr Error" still persist on the display when the 11c
appears otherwise unresponsive? It may be the LC oscillator
failing to start up coming out of power off. If you have
access to an oscilloscope you can check for activity of the
LC tank when the ON key is depressed.

I've seen the r2d2 lock up on occasion and give the external
appearance the unit as a whole is defunct. The dropout voltage
for the cmos process used in voyager silicon is phenomenally
low (a good thing). Removing the batteries for even a few
minutes I've often found insufficient to cold reset the device.
Shorting the battery terminals however will discharge the
bypass capacitor and do the job.

Other than this there isn't too much which can commonly go
wrong with a voyager to make it appear defunct. Grab a
5-10x jeweler's loupe and have a look at the SMD solder
joints on the lqfp packages. It is possible an intermittent
connection has developed. In that event pressing down on any
suspect lqfp leads with a wooden toothpick while trying to
bring the 11c back to life would be my suggestion.

[Antonio Petri (UK)]

Thank you for your detailed diagnosis. It happens that after about 8 hours since I removed the batteries the calculator is working ok again, I haven't done anything but putting the batteries back in. Yes, the "Pr Error" message stayed even when the calculator wouldn't respond to any key press; it disappeared when I removed the batteries for the first time. After putting back the batteries after about 15 minutes the calculator didn't turn on at all. So, I understand that, if it happens again, I will have to short the batteries' contacts, as you suggest, or... wait 8 hours again!
Thank you again,
Antonio