Casio fx-180Pa calculator: An easy fix for LCD display missing segments

[jebem]

Yet another typical education calculator supplied with an hard plastic protective case (not shown here).

Feature rich calculator for such a low cost machine imho.
It feels very light on the hand due to the cost reduction design choices.

This unit developed a fault in the LCD display, common on this type of calculators, due to the fragile flex PCB used in it.
There were missing segments in some digits. Although it was a easy fix. See below.

The calculator after being repaired.




This is an ugly back cover. Although, there is a reason for this back cover concavity.
This calculator uses the back cover as part of the keyboard assembly. Casio used this approach on other models too, like the ultra light and compact Casio fx-3900Pv model.




This is an unbelievable low current consumption design and yet it is powered by a huge high capacity AA 1.5Volt battery cell.
Average power of just 0.00003 Watt translating to an avg current of just 20µA.
The battery will last forever until eventually starts leaking and destroying the internal circuits if not timely removed from service.




The keyboard keys carbon contacts are installed at the back cover.




There is no conventional rigid PCB (print circuit board).
The keyboard matrix and SoC processor are deposited on a ultra thin plastic foil acting as a flex PCB that is fixed over the keyboard membrane by using melted plastic rivets.

And there is no soldering at all either.
The battery bypass electrolytic capacitor leads are just melted to the plastic front cover, as well the battery terminals, and they connect to the main flex PCB by just the natural elastic nature of the parts with the help of the back cover.




To fix the missing LCD segments, I used an very old trick that can work most of the times on this kind of LCD "flat cable" connections where the "wires" are just conductive paint deposited over a thin plastic foil.

Because the are no real wires and no conventional soldering involved, we can't use conventional tools and techniques to fix it.

However plain hot air can fix this kind of faults.
So I used a conventional air dryer over the flex PCB near the LCD "flat cable" interconnection for a couple of minutes. Job done. I got a new high contrast LCD display.