Problem with my 11c

[hayesbd]

Hi, folks! New member, here...

I have an 11c that has been my trusted companion since college (1985) and a few months ago, the millionth drop caused a broken lcd. I just replaced it with an lcd from a vintage 12c since that was less expensive than sourcing a complete 11c. When I had it apart, I noticed that the ON key was not working correctly, even before the screen replacement (there was enough of the screen still visible).
To make a long story short, I got the lcd replaced just fine, but the problem with the ON key still persists.
Essentially, the calculator works, but cannot be turned on with the ON key. It will turn it off, though. Most any other key will actually turn the calculator on, but will display random results. I can clear the display and it seems to then work normally. With the ON key not working, the self tests do not work.
I shorted the battery contacts with the batteries in place and that allows the ON key to power up the calculator (once) and displays Pr Error. Again, clearing the display allows it to work apparently normally.
I am willing to live with it this way, but before I button it back up completely, I wondered if there is anything left to try.

Many thanks for any help you can provide.

Regards,
Brian

[Katie Wasserman]

What happens when you run a keyboard/LCD test: "ON" + "\(\div\)"? Does the ON key turn on the 2 segments on the LCD that's it's supposed to? Do all the other keys respond correctly?

[Geoff Quickfall]

After answering Katie's question try the following .

Press gently on the back of the keyboard at the on key location, with the rear shell off. Now cycle the on off key while continuing to press, to see if it works. Also check the heat stakes around the on key, for integrity.

If still no joy, then try introducing some DeOxit gold in liquid form through the pin hole in the back of the keyboard corresponding to the on key. If no DeOxit use rubbing alcohol or some kind of contact cleaner. It may be that non conducting debris has entered the on key bubble snap.

Geoff

The red arrows point to the pin holes located in the center of each snap. Pictured are some of the heat staked families: voyager, Titan (71B), 41 full and half nut.



Once done the display test should yield the following:

[hayesbd]

Thanks for the replies. All the self tests simply turn the calculator on, sometimes with weird results. Clearing the display returns it to proper operation.

I will try the deoxit trick, but the button works to power off the calculator, just not on. All the heat stakes are still currently removed since I have just replaced the LCD.

Thanks again,
Brian

[Geoff Quickfall]

Sounds like there may be a cold solder (weak solder) joint on the chip. Lots of drops over the years.

When you are sure that the key is not the problem the next step is to check the solder joints on the PCA (printed circuit assembly). It could be that the last drop caused a intermittent connection problem to an IC on the board.

Is this the board in question?

[Geoff Quickfall]

Just read your answer! As I said above, check out the IC's solder points. Obviously no need to introduce the DeOxit through the pin holes since you have access to the opposite side. It sounds like the IC is not getting the signal from the 'on' position but only the 'off' and yet for some reason any other key does send an 'on' logic to the IC.

Geoff

[hayesbd]

Geoff,

Thank you, thank you, thank you! I found an unsoldered terminal! I'll get it back in order and report my results.

This calculator has been through a lot with me. I once accidentally dropped it into a bucket of house paint and, of course, had to rinse off all the latex paint, thoroughly soaking it inside and out. A week later, it was dried out and working fine once again!

I have used this calculator almost every day of my working career for the last thirty odd years. I am amazed at how discombobulated I have been trying to use a crummy TI algebraic calculator (I use this term loosely here) for the last few months.

Since I have many years left (I hope), I want to procure a backup if this one ever dies permanently. I was leaning toward another 11C/15C, but have seen a lot of glowing reviews about the 32SII as well. What would you folks recommend? I really don't program much, preferring MathCad or Excel for that. I just want a reliable/ergonomic/durable scientific RPN calculator.

Thanks again,
Brian

[hayesbd]

Geoff, et al,

Woohoo! Happy, happy, joy, joy! It's now functioning perfectly and self tests work properly. I cannot express profoundly enough how grateful I am for your help. It's probably the ugliest example of the 11C out there, but it still works and is ready once again for the rest of my engineering career!

Brian

[Geoff Quickfall]

Good news!

There was a remake of the 15c out there, more memory then the 11c, compatible programming and super fast, plus fits in your pocket.

Or just another normal 15c as the prices seem to have dropped. I like the 15c for the programming room and pocket ability.

The 32sii is great, have one but if you are doing that go with a 42s.

Caveat though, if all you need is a 11c then upgrade to the 15c would be my choice, familiarity and all that.

Glad it worked.

Geoff

[Ed Wright]

Brian, So glad you were able to salvage your trusted 11C. I was also amazed to read about dropping it in a bucket of paint and salvaging it from that - amazing.

Geoff, What am I missing? You posted a picture of 15C with an LED display and there is not one comment about it? Is it an inside joke I missed somewhere along the line?

[Geoff Quickfall]

Yep, I was wondering about that too :-). Maybe I slipped it into the post too subtlety!

It was an April fool joke I posted about 5 years ago on the other forum about my wishes for the new 15c LE.

Oh well

Yes, glad the 11c is working also, Merry Christmas.

[Thomas Radtke]

(12-26-2013 08:26 PM)Geoff Quickfall Wrote:  It was an April fool joke I posted about 5 years ago on the other forum about my wishes for the new 15c LE.

And HP listened! They left out the LED display (darn marketing people!) but implemented its power consumption ;-).

Edit: Almost forgot - very nice you both managed to get that gravityphile 11C back to work.

[Geoff Quickfall]

Gazing! Ouch!

Take that hp!

:-)