HP15C - differences in displays


Hi to everyone!

I was very surprised when I was trying to replace one 15C bad display for an HP12C display and they were not the same.

The 15C has a higher serial number than 12C: 2901B17387 versus 2534B96550.

Note the contacts in both displays and PCBs. The old ones are thin and compared to the newest model.

Old HP-12C

Newest HP-15C


Could you please post the part numbers of the chips in both calculators, as well as the part numbers of the circuit boards (typically 5180-xxxx, 00xxx-600xx, or 00xxx-800xx)? If it's not too much trouble, high-res photos of both sides of both boards would be nice. I'm collecting info for my Voyager internals web page, and would like to link each entry to example photos.

I'm guessing that your 15C has the 1LQ9-0325 processor and uses a 4:1 multiplexed display instead of the older 2:1. The 4:1 mux only needs about 29 contacts (25 segments x 4 backplanes), vs. about 52 for 2:1 mux. The drawback of the higher mux ratio is that the contrast isn't quite as good.

Unfortunately the displays aren't interchangeable, as I's sure you've realized. But it shouldn't be too hard to find a 12C of comparable vintage to the 15C, which should then have the 4:1 muxed display.

Best regards,


Edited: 22 Oct 2005, 10:57 p.m.


Hi, Eric

On the weekend I'll take the pictures, ok?
Best regards

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