15C all functions work, but can't self test

[Todd Bloss]

Hello,
I have an old HP 15c that I "inherited" from my uncle.
I'm trying to learn to use it and though it seems to execute all the functions properly, I cannot get it to do the self test or the keyboard test.
Instead of it going into test mode, it just turns on.

I know to hold down the x key, then press the "on" key, then let go of the x key, but no joy.

If anyone could help, I'd appreciate it.

Thank you.

[Raymond Del Tondo]

Hi,

maybe you mixed up the order of keys you have to press/release.

Before initiating the key sequence,

the calc has to be turned off.

Then:

1. Press and hold the 'x' key.

2. Press and *release* the 'ON' key.

3. Release the 'x' key.

Now the self test starts. After finishing, all segments are lit.

To return to normal mode, just press any key.

HTH

Raymond

Edited: 27 Aug 2004, 1:51 a.m.

[Todd Bloss]

Yes, I'm sure I've done the sequence correctly,
In fact, I just put in a new set of Duracell batteries and tried the test again and it worked like a charm.
However, after getting it to work once, I now cannot get it to do it again!

Very frustrating :/

Thanks for your help though.

[Randy Sloyer]

Strange as it may sound, chances are you have a bad memory backup capacitor. Take the batteries out for 30 seconds, then put them back in. If you see PR ERROR, you have a bad capacitor. The capacitor should hold memory for at least five minutes so the thirty second test is usually enough to determine if it's a problem.

The value of the part is 22uf but it can be a standard radial leaded electrolytic or a surface mount tantalum - it depends on the age of the unit. I've never seen a tantalum fail, only the standard electrolytics.

[Todd Bloss]

Found the problem. I was trying to make it do the test again immediately after a test. If I just let it sit for a minute, it can do the test again perfectly.