HP-15C with display problem

[Robert Graulich]

Hi folks,

I just got my hands on a 15C. It works fine, but the display seems to have a loose contact. I.e., the rightmost digit is missing its lowest stroke, and the PRGM annunciator does not show up. Two times I could observe that the same stroke is missing at the second digit from right, and then the C annunciator is also missing.

Is it worth to try to fix this? For sure, I can live without PRGM, but the missing stroke sometimes looks confusing, especially when editing a program.
Does anybody have experience with this kind of faults? Is there any text how to do it?

I looked at some pictures of the 12C, and it seems that the display is the same. Is it possible to implant such a display into my 15C?

Robert

[Nelson M. Sicuro (Brazil)]

This problem was discussed here in the forum some time ago, please do a search on it.

If is not very easy, you may need to remove the PCB to access the display and clean its contacts. To remove the PCB you will need to "shave" the tops of several (41) plastic "bolts", save them, and melt them again (pressing the PCB very hard!) to let the keyboard as good as new (and clean it, it is a very good opportunity!). If you haven't practice with a soldering iron or sensitive electronics I suggest to send to someone that can help you.

Good luck!

Nelson

[Randy Sloyer]

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv013.cgi?read=46995

Is a good thread to read. Consider it could be:

1. A loss in connection between the cpu and lcd.
2. A bad lcd.
3. A bad cpu.

The first one you can fix, #2 will need a replacement from a like generation 12C and #3 - well, sorry, that's bad news.

[gifron]

Randy and Robert, in my case, it turned out to be a broken solder joint on the CPU (I guess that's what that chip was).

Before you shave the plastic welds to check/clean the zebras and lcd contacts, do this: With the back off (and with yourself grounded, of course), turn on the calculator, apply light finger pressure to the body of the chip, and check the display. If this fixes the problem, it is likely that you have a broken joint. How to resolder such a tiny connection is something I can't help you with, whch is why I'm still missing a segment on my 15C.

[Nelson M. Sicuro (Brazil)]

The big chip is the LCD controller + RAM + ROM, the one in the middle is the additional RAM and the other (on the right without the back cover) is the CPU (if your 15C is an older one).

Take a look on the "zebra" contacts, if they are somehow "bent" inside the mounting. When I mounted one there was a lot of missing segments, when you assemble the display the metal frame "bent" the zebra, you have to be careful.

Best regards,

Nelson

[Eric Smith]

Quote:

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the one in the middle is the additional RAM

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The one in the middle is additional RAM *and* ROM.

[Nelson M. Sicuro (Brazil)]

Very interesting, this is new to me! I think that is time to gather all information we can about the Voyagers and build a website or a very complete article!

Best regards,

Nelson

[Robert Graulich]

Thank you for the link. It seems that I have one of the very early models. I will take a look into it at one of the next weekends.

Robert

[Michael Meyer]

I usually can't sleep at night if there's a calculator to be repaired.... glad you aren't that bitten....

[Randy Sloyer]

You should see a doctor with a problem like that, I'm sure there is hope for you.