HP-32E Advanced Scientific Calculator - my first Spice machine

[jebem]

This is time to assemble this machine, even if I have no time now to make new custom battery clips.

Soldering new clips is not a good idea as it will isolate the connection to the flat cable traces in the back.
However that's what I have done to be able to test the calculator.
Of course after all this heat I got an isolated connector with about 18 Ohm resistance.
So I have used an old trick on these cases: have soldered a thin wire between the battery connector and the flat cable copper trace.

Power supply back in its place in the plastic frame.
IC's lay down having pin1 pointing to the power supply.




Now it is the flex PCB assembly turn.
The brackets are prepared to be inserted on both sides.

A small detail concerning grounding.
This design uses positive common ground circuit.
Once the right side bracket is inserted (having the keyboard facing up), when the power switch is ON the battery positive side is connected to the metal frame.




Cleaning the PCB traces is essential for good operation. I use isopropyl alcohol with good results.



And at last the big moment. Testing the work done.
I used a set of two 1.5V AA depleted batteries for a total of around 2.5V when loaded.

In order to be able to test the PCA out of the case, I had to solder three thin wires to bypass the power switch. Used wrapping wire AWG33. But the thinner the better.
A low melting point solder is essential here.
Adjust your soldering station to an adequate temperature. Too low and the flex PCB will be destroyed as it will require more time to solder.For this job I have used a regular Antex CS18 18Watt thin tip soldering iron and leaded thin solder "Wonder Solder" by TRT.

This is a simple procedure but requires special attention when soldering the wires because the flex plastic material is extremely fragile and seems to have a low melting point.
Therefore tinning of the flex traces is not recommended. I have just tin the thin wires and then while heating the wire just pressed it briefly (less than a second) against the flex traces using the soldering iron tip.
Clean and easy task.



After a couple of minutes, I got the battery low indicator.
At the time the batteries had 2.30V.




Initial current consumption of 103mA after power on.




The self test (STO followed by ENTER) passed without errors on every check I have done.
All LED display segments lit resulted in around 202mA.
I have no references on current consumption on these HP models, but it seems a little too high even for this design and technology.
Perhaps the DC-DC converter power supply needs new capacitors, but I will leave it as it is for now.



(Continued)