How to open a HP 28S calculator

How to open a HP 28S calculator

  1. Problem
  2. How to open the HP28S (right side)
  3. Cleaning the contacts
  4. How to open the HP28S (left side)

See next post for creating a new HP28S case


Key row ‘Y’ to ‘)’ and ‘EVAL’ to ‘-‘ are not working

How to open the HP28S

Since I could not find any photo instructions on how to open a clamshell calculator HP 28S, and I would like to fix this problem, I decided to read up on the different text descriptions on how to do it and started to document it with pictures.

So first set of pictures from today 25.Jul.2017

Picture 1 I started to heat the bottom right corner first (and it worked great)
Picture 2 Heat is set to 2 out of 10, I think a hairdryer on the lowest setting works also
Picture 3 Warming row by row
Picture 4 Some pegs were already broken, so they lifted automatically
Picture 5 cover removed (maybe 5min)
Picture 6 removed cover from the back
Picture 7 Now the top, starting in a corner
Picture 8 So also the top sticker made it.
Picture 9 this took about 2 more minutes
Picture 10 close-up, you see that some pegs broke of (Calculator is 30 years old)

Some close-up pictures

Picture 11 Just one pin that broke off (age of the calculator)
Picture 12 close-up where the pin was in
Picture 13 close-up with the pin added again
Picture 14 pin half way removed
Picture 15 just a measurement so I have an idea for the size of the drillbit, looks like the hole is on top 3.2mm in diameter, so a good size to start with would be 3mm

Next step: (in a few days)
I am buying a small used drill press or maybe just a stand for my drill, so I can remove the top of the melted plastic peg/pins.
Today August 5th 2017 I picked up the drill press.

Picture 20 starting to drill the bottom rows first
Picture 21 Not drilling really deep, just about 1mm
Picture 22 Sometimes a pin breaks but mostly the head comes off
Picture 23 Now the top section
Picture 24 About done with drilling
Picture 25 calculator is open, some small pins I did not even drill
Picture 26 the keys are all loose
Picture 27 the cover from the top
Picture 28 the cover from the bottom
Picture 29 the bottom piece
Picture 30 the drilled out heads and some pins that broke
Picture 31 close up back of display
Picture 32 close up bottom piece

Cleaning the contacts

We now have the right side (the one with the display) open and the idea is that if a contact is dirty it could prevent a whole row or column of keys to NOT function. Well lets try cleaning them

What did I clean

Picture 60
Use a Q-tip with alcohol and clean it. I also like using a soft eraser on the gold contacts.
Picture 61 carefully clean the foil with the q-tip
Picture 62 Lets see if that worked and put it back together based on the picture
Picture 63 Who would have thought. Keys in that row are working again
Picture 64 Just assembled it quickly to test
Picture 65
This shows which contact has the problem. The initial problem showed an entire row not working so based on this picture this would be “12” needs extra cleaning

How to open the HP28S (left side)

Lets open the left side

Picture 40 starting again in the right bottom corner
Picture 41 slowly heat row by row and pull
Picture 42 overlay removed, no issue
Picture 43 lets start drilling again
Picture 44 sometimes the peg is broken on the bottom and comes right out
Picture 45 all are drilled, ready to open
Picture 46 the stuff that was removed during drillin
Picture 47 carefully pull on a corner
Picture 48 its removed, do not worry about the keys
Picture 49 now open the hinge, use a knife and screw drivers
Picture 50 left side is now also open
Picture 51 final picture

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