Creeping black pattern on HP-11C screen


My venerable 30 year old HP-11C is getting a black splodge on the LCD screen (when calculator is both on and off), and seems to be growing with age. A photo of the problem is below.

Can anything be done about this?


HP-11C photo LCD problem


The only way to fix that is to replace the LCD assembly with another one from the same era. It can be from a 12C, which is of course the easiest to find.

On later units, HP changed the display multiplexing, so the displays aren't interchangeable with the older units. I'm not sure exactly when that happened.


you should post a picture of the battery contacts. That would help forum members guide you on what era LCD you should look for.


OK, here is a photo of the battery contact:
battery contacts

Also the serial # is: USA 2716A13463 (if that helps).

So what version of HP calcs can I get the LCD screen replacement from?



Yours is a later model so you should look for a 12C with srarting serial numbers close to yours such as 24, 25, 26. I don't know how early you can go, but I am pretty sure these would have compatible LCDs. Good thing is there are plenty of 12Cs around.

edited to remove 27 & 28. Thanks Randy

Edited: 12 Apr 2013, 9:23 p.m. after one or more responses were posted


I would avoid serials beginning with 27 and 28. They changed the 12C design late in 1987 and the replacement unit might well have the wrong version LCD. The 15C and 11C change followed the 12C sometime later in 1988.

The way to know for sure is be the number of IC's. Your 11C should have two and the LCD must come from a 12C with two IC's as well. If you open your donor 12C and see only one chip, the LCD is not compatible.


A 27xx serial number indicates manufacture in 1960 + 27 = 1987; etc.

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