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HP Forum Archive 13

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15C Display Repair
Message #1 Posted by gifron on 17 Nov 2003, 11:29 a.m.

A coworker has a 15C in which one of the segments works intermittently. Is this likely just an insecure connection? Is it a pretty easy fix?

Re: 15C Display Repair
Message #2 Posted by Nelson M. Sicuro (Brazil) on 17 Nov 2003, 2:05 p.m.,
in response to message #1 by gifron

I fixed several Voyager-type calculators (11C, 12C, 15C) but there are two types of internal assembly: the newer ones are the most dificult to access the display, as the PCB is "riveted" with plastic pins on the case. To clean the display contacts I had to remove all 41 plastic rivets. The display worked but the keyboard became "noisy" (loose keys, as I cannot put enough pressure when re-melted the rivets).

The older ones the display/chips are separated from the keyboard, it was very easy to clean them. Just take care with the keyboard contacts, as they can be a little loose when closing the case and the keyboard doesn't work.

Good luck!


Re: 15C Display Repair
Message #3 Posted by John on 18 Nov 2003, 3:39 p.m.,
in response to message #2 by Nelson M. Sicuro (Brazil)

Nelson, You said that "the newer ones are the most dificult to access the display..."

I was wondering, when would you guess that they made this change to the "newer ones?" I'm looking to pick up a used 15c. Would you recommend I find an older one because it's easier to repair? Maybe it doesn't really matter? Just want to find the most reliable Voyager possible.


Re: 15C Display Repair
Message #4 Posted by Nelson M. Sicuro (Brazil) on 18 Nov 2003, 7:01 p.m.,
in response to message #3 by John

The problem is that if you have a older model, you NEED a older display, and vice-versa. The display mountings are different... If the first two digits of the serial number (plus 60 is the year of fabrication) are equal, I think that there is no problem. The displays of the 11C, 12C and 15C (and I think 16C and 10C also) of the SAME year may be identical, and you can buy a cheap 12C (of same year) to use its display. I've done that two times, one compatible, other not (different years), and I discovered these display differences.

My HP-15C of 1987 (s/n 2723Bxxxxx) display is the same one of my HP-11C (s/n 2644Bxxxxx) but are different of my 12C (s/n 2808Axxxxx) and the oldest one is a 12C (s/n 2317Axxxxx, its display is the easyest to replace).

If your 15C have one helical spring on the battery compartment in only one side and a fixed gold contact on the other side, it is the hardest to replace the LCD. If it has two simple folded springs, it is the older and easyer to replace.

I already counted three diffent displays, all incompatible with each other. Take care when searching a replace!

Good luck


Voyager LCD variations
Message #5 Posted by Randy Sloyer on 18 Nov 2003, 8:25 p.m.,
in response to message #4 by Nelson M. Sicuro (Brazil)


You are correct: The entire Voyager line (10/11/12/15/16) used the same displays, but not always at the same time. So, I would like to add the statement: "Most of the time". This is especially true as you found out with later model 12C's. They where always the first to change methods, the 11 and 15's followed. I've started to track the versions and serial numbers, but I don't have enough data yet for it to be useful.

I must disagree with you about the easiest version to find. It has been my experience that the older the unit, the harder it is to find a display for it. Volumes did not start to build for a few years after introduction so there are fewer old units. I'll bet there are 1000 new 12C's out there for every single older USA unit.

I have been able to identify three different versions with two being somewhat compatible. I refer to them as "fine pitch" and "coarse pitch".

The earliest version is the unit with separate keyboard and logic board parts. These can be identified by the springs in the battery compartment - straight contacts on either side, no spring. These are the hardest to find and to work with. The LCD is a "fine pitch" version that is held in place with the metal frame. It is positioned poorly by the frame.

I think due to the cost of manufacture, they re-engineered the unit to be one circuit board. This is where the coil spring on the left side of the battery box appeared for the first time. The same "fine pitch" display was used, but it was mounted by means of two-sided tape to an intermediate plastic carrier. The carrier had two indexing pins which made the job of properly aligning LCD as we say, "A piece of cake". Now that the LCD sat further away from the circuit board, the zebra connection strips got longer.

At this point, I would like to say that these two "fine pitch" versions are compatible. If you have a fine pitch LCD on a carrier and need one without, a little UN-DU (heptane) will pop it off for you. The same is true in opposite, if you need one with a carrier, you'll have it on the broken one, just remove the broken one and stick the carrier-less one back on. Just examine the LCD position on the carrier before removing, it will match up in the Y direction, you'll just need to center it in X. Use the proper length zebras.

Somewhere around date code 28 (1988), they redesigned the circuit board (again) and changed the spacing and width of the connections on the LCD. I suspect the desire was to ease alignment problems in assembly. These are what I refer to as the "coarse pitch" version. This one is VERY easy to find, just get a throw-away Chinese 12C and you're set. Yes, the LCD version used in the 3 volt units works just fine. I have only seen 11, 12 and 15C's with this version. These are VERY easy to change out and almost never have missing segments since the pads are so much larger, a drop to the floor will not cause misalignment.

I believe the 10C was only built in the two board version but I have not been able to verify. I know the 16C was built in both (I own 2 as I was a software geek first) but never made it to a coarse pitch version as it died a premature death.

Hope that helps.

Re: Voyager LCD variations
Message #6 Posted by Nelson M. Sicuro (Brazil) on 19 Nov 2003, 5:56 a.m.,
in response to message #5 by Randy Sloyer

I didn't know that the production amount of the earlier models was smaller than the new ones.

The "fine" pitch contacts LCD of the earlier ones have 56 contacts, and is 1:2 multiplexed (the lower contacts and upper contacts have distinct common1-2 backplanes, can be used as 1:4 multiplex), and is the one with best contrast and no "shadows" on it. The "coarse" one have 30 contacts, and is 1:3 multiplexed and have "shadows" of the segments (you can see the "off" segments if you look at a shallow angle)

I'm trying to build a "timeline" of the voyager models and variations, but I don't have much information also.

I noticed that the "flex board, fine lcd" ones (earlier) have a 2 or 3 chip assembly (11C and 12C, 15C resp.) and I have two "one board, fine lcd" (11C, 15C) that uses the same chips (2, 3 resp.). I have a 12C "one board, coarse lcd" that uses a single chip. I thing that it was the big change on the voyager line, a cpu/ram/rom/lcd controller on one chip instead of cpu + lcd controller/rom + ram (15C).

I also discovered that on the 2/3 chip version the rom CAN be extracted, with logic analyser of some sort (or a parallel port with an adapter on PC and a good DOS software). The CPU is almost the same as of the HP-41CV halfnut (differs only on the clock/voltage). I plan to build a voyager's emulator as soon I get the rom out of my 11C/12C/15C.

I plan some day to build a site with pictures of the voyagers, but I haven't much time now...

Best regards,


Re: Voyager LCD variations
Message #7 Posted by gifron on 25 Nov 2003, 9:39 a.m.,
in response to message #5 by Randy Sloyer

I have a 15C with a missing segment (sixth character from the left, bottom segment). I have cleaned the board contacts and the zebras with alcohol and eraser, to no avail. I did not clean the display-end of the zebras, as they are adhered to the display, and I didn't know if I could peel them off without damage.

The zebras seem to be making contact, except for the hard to overlook fact that the segment is missing. I have discovered that a very, very light flexing of the board causes the segment to activate. Is this another instance of the rubber getting old? Do I just need to replace the lower Zebra with one from a newer 12C? Having read the other posts, I'm aware of the differences in the displays, this one having the indexing pins on the plastic carrier - Are the zebras all the same?

Thanks again, Randy for your previous helps.

Edited: 25 Nov 2003, 9:40 a.m.

Re: Voyager LCD variations
Message #8 Posted by Nelson M. Sicuro (Brazil) on 25 Nov 2003, 10:13 a.m.,
in response to message #7 by gifron

The "zebras" aren't equal, the earlier models (those with flexible circuit board) are thinner than the new ones. If the missing segment activates with a light "twist" on the PCB, you may have a bad contact in one trace of the PCB. I found also that the mounting of the LCD is a little "tricky", when you put the mounting in place the "zebras" can be a little bent and when I tested it I found several missing segments. At first I cleaned all contacts, to find later that the bent zebras are the guilty...

Good luck!


Re: Voyager LCD variations
Message #9 Posted by gifron on 25 Nov 2003, 11:32 a.m.,
in response to message #8 by Nelson M. Sicuro (Brazil)

Thanks for the comments, Nelson. Yes, one has to be careful to keep the zebras straight. The same missing segment was there both before, and after, my repair efforts. I also inspected all the traces with a lighted 10X magnifier, and they all look good.

My actual question about the zebras being the same is, are they the same between models, assuming they have the same display type, as mentioned in the earlier posts by Randy and others. I would think they would be. That is, a thicker zebra from a 12C would work in a 15C which also utilizes the thicker zebra. Or to put it another way, are all voyager "thick zebras" the same?

Also, can I remove the zebra without being careful about how I position it in reassembly? My assumption is that all the dark sections are identically conductive, with the light sections being nonconductive.

Re: Voyager LCD variations
Message #10 Posted by Nelson M. Sicuro (Brazil) on 25 Nov 2003, 4:20 p.m.,
in response to message #9 by gifron

Do you tried to swap the upper "zebra" with the lower?

I think that the conductive area of it is the thin dark layer inside.

If the "zebras" from other HP-1xC are from the same size, it will work.

Try to test with another display if you can (if you can get another to pull the "zebras" out, get its display also if it is the same pinout). Some trace in the glass of the display may be defective.

Best regards,


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