After a long time I just happen to click the bring-back-the-HP15C-site and notice that the calcs counter has reached well over 200.000

It has been dicussed before that HP wouldn't bother to make a few thousands of calcs, but I guess that this amount is becoming economically interesting, isn't it?


Yes, but how many of that 200,000 would really translate into sales? There's a big difference between filling in a number on a website and actually shelling out the money. Also, with only 3300 users having checked in, that averages some 60 HP 15Cs each. Very doubtful! I suspect that some joker(s) punched in some big numbers to make an average like that.

Also, re the $400 average EBay price: I bet the selling price would fall very rapidly if the supply increased significantly. I believe economists call a supply-demand relationship like that "inelastic."

Bottom line: I don't think the site provides much evidence for big 15C demand.



Actually it was two jokers or really probably one that made two entires. There are two signers that have said they would purchase 99,999 calculators. The names on those 2 entires are Bill Hewlett and David Packard. Then there is a guy from France that "wants" 5,000 and 2 in China that "want" around 1,000. If you disregard these 5 entries, the number drops to a more believable level of 11,707.

I keep the web site up mostly as a tribute to the 15C. Maybe someday if the site ever gets any real publicity the number of signers will move in to a high enough range to mean something. One of these days I will add more content with more help and information about the 15c with sample programs and stuff.

Chris W


When my HP15C broke down after 15 years of daily reliable service, the
autopsy of the corpse reveiled the incurable disease of hairline cracks
in the flexfoil wiring. Tried to fix it with a very fine soldering iron, came back to life for a short time, then another crack. In the end I had a dozen or so jumper wires soldered in and then dumped it into the garbage can. The flexfoil wiring was brittle like an old man's bones.

The more interesting point is how long I phoned around and ran up and down in town and all sorts of suspicious places where they use to sell NOS electronic gadgets. No trace of any HP15C anywhere. Even at $10 per hour, I think I could have bought an handful of them back in the good old times, just for the time I spent in vain searching for a replacement. I finally finessed a lowly but unused HP11C away
from my father, a retired engineer, for a few bottles of valuable
Bordeaux wine from my cellar. He had had the foresight to buy two of the last HP11C in town when they sold out.

Bottom line of this story: if all of the 10,000 or so HP15C aficionados who truly signed up on that list have invested about the same time, effort, and precious collectibles like me just to get a replacement, this translates to an amount of money where we could have reverse engineered and perfectly copied it even without any help of HP.



Hi, Bernhard;

I have on HP15C withthe same problem: the conductive trails of the flex circuit began to crack. I tried to solder them, but found no long-lasting solution I could think of.

I was given an HP11C with a broken LCD, so I used the case and internals to rebuild the HP15C. I had to remove the keyboard faceplate and the back label of both calculators, but it was somehow hard to remove the HP15C`s back label, so I was only able to use the riginal HP11C case with the HP15C's keys and keyboard faceplate. I also mixed the IC`s, so I used an earlier Voyager processor with a newer R2D2 (after reading it from a serious contributor, I cannot help thinking of the little StarWars robot, but in this case, R2D2 stands for RAM-ROM-Display-Driver...) withthe original HP11C mainboard, because the HP11C had the single maiboard structure. My little frankencalc survived the first lightning ("It`s alive!!") and it is working fine till today.

I wonder if there is a way to build a thin fiberglass PCB that fits the same as the orignal flex PCB so we could rebuild the Voyalgers with this sort of problem. Instead of using the small polymer, we could add a connector like those found in many portables available today.

I have the pictures of the inside of the rebuilt frankencalc, but I have to find them prior to post again. I`ll let you know.

Best regards.

Luiz (Brazil)

Edited: 14 Aug 2005, 2:44 p.m.


Hi Luiz,

thanks for the info / hints: now I do know the flexfoil wiring disease is most likely not a single event with these HPs. Your hint with building a frankensteinian HP out of the worn HP15Cs chips and the HP11C comes too late, I threw the remains of the HP15C into the waste basket years ago, before I became aware of the exorbitant prices even badly worn HP15C corpses fetch on Ebay. I could have at least sold the keyboard (which still had worked perfectly - after 15 years of hard engineering work, I did all my calculations with it on a daily basis), and possibly recover all the money I had paid for my HP15C back in the early 1980s... this feat, if accomplished, would have meant to have got HP calculation services over 15 years for free !!! This is the kind of bargain I like. However, I remember my HP15C had needed a set of three expensive batteries after 10 years of service or so. Maybe I could also have sold them on Ebay as being "perfect condition, at least still half full" to fully exploit the HP15C corpse. No I'm no Scotsman but only joking about the strange show we all can see on Ebay with HP calculators as the main protagonists.

best regards,


Regarding the flexfoil, there is such a problem on another (non-HP) machine, the (very nice) eMate made by Apple years ago. Someone created a replacement part, see http://www.pda-soft.de/ematecable.html for a review.
So it can be done.
Is it possible to solder a bunch of small wires instead of this dreaded flexfoil ?


On the HP15C the flexfoil actually carries all chips, the display, and links this assembly to the keyboard, which is a real PCB. I think it's
almost infeasible to replace the flexfoil with another one. Desoldering the precious chips and putting them on a real PCB won't help either because this assembly would be thicker than the flexfoil.

I still wonder what causes the failure of the flexfoil. The HP11C I am using now also has one, and if this one dies, I have to take one of the LED HPs from my collection to do my daily calculation work.

Of course I could use an emulator such as Nonpareil on a PC, but having a real HP keyboard instead of a mouse is more efficient.


Hi Bernhard, all;

I know this is not the thread's main issue, but I`d add that a thin fiberglass PCB built with the same layout found in the flexfoil would be a possible solution. I disassembled an HP41CV halfnut once and the hibrid LCD controler + RAM-ROM (an earlier RADM-ROM-Display-Driver?) is assembled in a thin PCB. If this PCB in an earlier Voyager has connectors in the same configuration found in the connecting edge of the flexfoil, I thnk it can replace it with some additional advantages.

I still have the old flex-foil, and I remember I scanned it. Would someone try something like this? I have no such thin fiberglass PCB, but I think it`s worth trying.

Best regards.

Luiz (Brazil)

Forum Jump: