HP 15C All segments on

[howardlong]

Folks,

I just received an HP 15C supposedly in full working order from an eBay seller. It arrived with no cells installed, so I inserted three brand new ones.

As soon as the cells are inserted, and before pressing any buttons, the display came up with all segments on, including annunciators.

The keyboard is apparently unresponsive, and I cannot turn off the display without removing the cells. Not even the On button does anything.

I've tried the shorting method a number of times after removing the cells to remove any residual charge, and measured that the charge has reasonably dissipated to a few mV. Presumably there's a capacitor in there to try to maintain the device's state while you change batteries.

On one occasion after discharging, when inserted the batteries the display came up blank instead, but following the same procedure again I am back to all segments on.

Does anyone have any recommendations or suggestions?

Many thanks, Howard

[rprosperi]

Have you tried the diagnostics and reset, described here?:

https://www.rskey.org/~mwsebastian/selft...tm#voyager

[Allen]

(05-26-2020 03:06 PM)howardlong Wrote:  As soon as the cells are inserted, and before pressing any buttons, the display came up with all segments on, including annunciators.

I seem to recall something like this happening to me once when the batteries were removed at completion of a self-test. It's possible the calculator is damaged? I read somewhere that in lieu of the "short" test, one could insert the cells backward for a moment.

I checked the user manual which only says reversing the cells "will clear Continuous Memory and could damage the batteries." So I assume the calculator is protected against reverse voltage. (maybe only try this with cells that are nearly dead anyway?)

If that does not enable key response ( I'd run the self check and keyboard check at the link Bob added), I'd say the calculator needs to be repaired.

Which brand and model batteries are you using? I like the LR44 or A76 batteries.

Not as common, but I've had problems with some of the cheaper Chinese batteries (apparently) not sourcing enough current on startup or during self-test, which generated lots of "Pr Error" messages each time the calculator went into brown-out.

[howardlong]

(05-27-2020 12:17 AM)rprosperi Wrote:  Have you tried the diagnostics and reset, described here?:

https://www.rskey.org/~mwsebastian/selft...tm#voyager

Thank you for your response.

Well I had already tried it to the extent that I can. The problem is is that the ON key (as with all other keys) appears to do nothing in the unit's current state.

I tried the method by turning it on by inserting the batteries with the various key combinations held down, but no change I'm afraid.

Any more suggestions will be gratefully received.