Hewlett Packard HP-32sII

There is a comprehensive review of this scientific calculator here:

Inside the HP-32SII
by Kees van der Sanden

This unit had a non-functional keyboard. Curiously, this calculator is not designed to be disassembled.

Let's see my repair...

Disassembly:

When removing the battery compartment cover, we can see 4 "rivets by heat ": the end of 4 plastic pins are pressed with heat after inserting the back cover of the calculator.

The inside diameter is 4mm. With a metal drill bit of this diameter, we can cut the plastic sealing.

As the plastic is very soft, this work has to be done by hand.

The four seals are removed.

It is only necessary to perforate 1 or 2 millimetres.

Now, very carefully and using your fingers (not metal tools), slowly separate the two parts of the casing.

On the underside there are four more "rivets by heat ". As the plastic is very soft, they can be removed with a little pulling, without damaging anything, and without cutting.

The PCB is held in place with six metal tabs, designed in such a way that when they are "closed" the PCB presses against the Display side.

The six metal tabs must be turned in the opposite direction to which they are positioned.

The PCB is now removed. We can see the two conductive rubbers of the Display, and the connection of the keyboard membrane.

We leave these components aside.

Diagnosis:

To test the keyboard, the diagram provided by Kees van der Sanden on his website is very helpful: Keyboard wiring diagram

Press and hold the ON button with a clamp, and check the resistance between the first two tracks with a multimeter.

After checking the whole matrix, the resistance is always less than 10Kohm: The keyboard is OK, so the problem must be in the connection between the keyboard and the PCB.

An anomaly is detected: The rubber that pushes the matrix connector against the PCB is very aged, and it does not recover after being pressed.

When the rubber/foam is removed, it is clearly degraded and no longer performs its function.

I cut to size two rubbers that I removed from a broken LCD. The rubber bands are the same thickness as the original.

The connector area of the matrix is cleaned with a soft cloth. Do NOT use alcohol or any other chemical product.

The elastomeric connectors must be positioned as shown in the picture, with the white side facing outwards.

I decide to test the calculator before bending the metal tabs, using some plastic clamps.

Be careful not to damage the Display, and not to scratch the border.

The keyboard works now!

Assembly:

Now we can bend the 6 metal tabs that hold the PCB.

With a pair of pliers and/or a blade, round off the tip of the 8 pins, so that they fit without difficulty.

The cover fits perfectly, and there is no need to do anything else at the bottom. On the upper part I decide to put 2 conical head screws, which do not protrude. This way I avoid using glue or other permanent fixings.

The calculator successfully passes all the TESTS.

Work done: