Products > Other Equipment & Products

HP-15C Limited Edition Tear Down and Why?

(1/2) > >>

The HP-15C Limited Edition have a problem with the blue function "g" key was not responsive at first pressing it.  The other keys worked well, but not the "g" blue function key.  I have e mail HP, but no replies and their supply of HP-15C Limited Edition is still wild by speculators.  I am stuck with a defective "g" key that HP has not interest to repair.  I taken it apart to try to try to access the contacts on the top side, but unable to.  The circuit board is melted plastic tight.  I can tear it down to be able to view the Atmel ARM RISC microprocessor.  There are three small, tiny springs to ground the top and bottom metal covers of the case that matches with the circle holes in the bottom plastic chassis with metal plate.  The two CR2032 Li batteries are wired parallel.  The circuit board has two separate 3 V DC input as seen in the picture with separate two blacks (-) wires and two reds (+) wires in parallel.  I am not please with the new HP after merging with Compaq, ARM, Digital, Tandem, and Kinpo.  I liked the old HP more.  Everything works on the HP-15C Limited Edition, except the "g" key, that needs a little wiggle or press in a tad more than the rest of the keys.

To open the HP-15C limited edition:
1. remove the battery cover
2. remove the 2 CR2032 batteries.
3. discharge yourself.
4. gently ply the four rubber feet and use a small Philips screwdriver and remove the larger lag screws.
5. remove the larger lag screw in the other inside of the battery compartment.
6. remove the small lag screw by the reset button by the battery holder inside the battery compartment.
7. There are six lag screws total, remember this.  The single smallest lag screw is the one on the lower right side of the battery compartment with a recessed underneath the lower right side battery holder corner.  Mixing the screws will break the case.  The larger lag screws are around the sides of the calculator. 
8. Use only fingers to ply the case free, be careful of the four battery wires battery.  They are delicately point soldered onto the main circuit board on the top side of the case and the battery is on the bottom side of the case. 
9. Be careful of the three spring grounding conductors on the two plastic sleeves at the corner of the case next to the lag screw holes and the plastic sleeve by the reset switch.  There are three springs two shorter length and one longer length.  Be careful to not pop, drop, or lose these springs.  The shorter length ones go to the corners and the longer length one goes to the top middle by the back of the display.  You will noticed the circular slots where these springs will make contact with the metal plate in the bottom of the case for grounding. 

I cannot take it apart further than this to repair the less responsive "g" blue function key.  I did reassembled it back to original and just use the calculator as is.  HP keeps running out of the HP-15C Limited Edition, so replacement is not possible and HP has not replied back.  There might be some contaminants on the contacts from the Kinpo manufacturer or defect in the contacts or it might be a capacitance keyboard like my Fluke 12 digital multimeter sometimes need disassembly to clean the key pad to work.  I have no way to tear it down further to try to repair the "g" blue key.  It works, but I have to press it more or wiggle it slightly.   I do not know.  I wished Kinpo would work on this problem.  I have this exact same problem on my HP-49G+ with the Symbols key that allows me to chose a function or graph software.  The Symbols key has to be wiggle to right side to get it to work.  I like the TI CX CAS in color more, perfected machine.

Battery consumption is very good to excellent.  I have not owned it for two years to be able to let you know how long it lasts in actual usage.  It is less than a month old, about two weeks old.  It can run on just one CR2032 battery with the second battery removed as it is a parallel circuit.  The memory is retained even with just one CR2032 battery.  Replacing the battery while retaining the memory is done by replacing one battery at a time, while leaving the second battery in place.  Once the first battery is replaced with a new one, then the second old battery is removed and replaced with a new one. 

I am sorry to hear of your problem. I have a bad key too, in my case the "sin" key. It only registers if I press it firmly, unlike all the other keys that register with just a normal press. Unfortunately I think their manufacturing and quality control is lacking.

In the past, HP have been quick to exchange calculators of it had a bad button. Usually without any argument.

It would be very disappointing if they just don't care any more.


HP calculators used to be designed and built to last, except for one hickup with their series in the mid seventies. Double injected keys, usablility as a prime concern, and accuracy were their reputation. My last HP calculator purchase was an HP48GX. Someone went insane in the design department starting that series. The colour scheme was alien and hard to see. HP engineers had worked hard on a colour scheme in the beginning to make finding things easy and quick. I understand that certain races have problems discerning certain colours from others easily and that the 48GX made it difficult for some.

Anyway, the next HP calc I buy will not be for nostalgia and just a cheap ghost of HP's former calculators like this 15C appears to be.

The latest 35S looks good, and I have been interested in the 50G. Of course, here in Chile they cost twice as much as in the US.

They took a massive backward step with the HP49 - their top of the line calculator at the time. The HP48 was extremely well respected, and the HP49 their next generation design. The current HP50G is basically the same calculator, except they have replaced the 4MHz HP custom processor with an emulator running on an ARM processor. The calculator code itself has not been changed much.

Designed in North Ryde, Sydney, Australia I seem to remember. They had some exceptionally brilliant programmers, but they were badly let down by the hardware designers, or more likely, the accountants who wanted to get extra Christmas bonuses through some inspirational cost savings.

They replace the quality hinged keys with the injected molded labels. Instead they went to cheap rubber keys, and I think they printed the lettering on the keys after the calculator was assembled! They were very proud of that cost saving as it meant they didn't need to get the right key in the right position.

Somehow Hp managed to go from the best calculator keys to the absolute worse keys in any calculator ever built. Quite an achievement!

The initial calculators were almost unuseable - the keys were very hard and unreliable, and the type of plastic they used over the display made the display almost unreadable.  The later HP49Gs had useable keys (but not great) and a different type of plastic display cover.  The only good thing about the HP49G was that they used a dud electrolytic capacitor across the input from the battery that stopped the calculator from even turning on.  This was good because I picked up about 8 dud HP49G calculators at about $5 each, replaced the capacitors, loaded the HP50G firmware and all have worked fine since.

For normal use though, they are far too complicated.

Why on earth didn't they keep making the HP11C/HP15C calculators that people actually wanted?



[0] Message Index

[#] Next page

There was an error while thanking
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod