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

It's a "Program FX" type calculator as Casio like to call it.

Typical education calculator supplied with an hard plastic protective case (not shown here).

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


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

There is a reason for this back cover large recession.
To reduce production costs, 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 a unbelievable low current consumption design although being powered by a huge AA 1.5Volt battery cell.
Average power of just 0.00003 Watt translating to an avg current of 20µA.
The battery will last forever until eventually starts leaking and destroying the internal circuits.

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.

There is no soldering at all. 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 pressure from the plastic foil 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 near the LCD "flat cable" interconnection for a couple of minutes. Job done. I got a new high contrast LCD display.

SHARP EL-5120 Programmable Scientific Calculator

The SOLVER machine.

Compact, well built, direct algebraic logic calculator, with a handy uncommon 3 lines alphanumeric characters matrix display, from 1994.

Obviously the SOLVER capacity is the main feature of the model complemented by its programming ability. I didn't spend my time checking it in detail, but, here are some highlights taken from the manual:

Powered by a single CR-2025 battery cell.  3mW power consumption.
Contrast adjust by software.

Display: 14 characters and 2 exponents x 3 rows, 5x5 dot matrix.
Number of display digits: 10 mantissa + 2 exponent
Number of internal calculation digits: 12 mantissa

Variables:
27 named global variables (A,..,Z, θ) persistent between operation modes.
9 additional named local variables in each equation or program.
Last Answer memory.

Total user memory capacity: 1211 Byte. 
Memory manager shows free memory.
Memory is shared between Variables, Programs and Equations.
Each variable consumes 8Byte (where its name takes 1Byte).
Each new Program structure takes 32 Byte; each line takes 3Byte plus the number of characters (1Byte each) or commands (1Byte each).


Setup allows to chose Deg, Rad, Grad, Floating, Fixed, Scientific, Engineering, Fractions.
 

It has four Operation Modes:

• REAL - Using real numbers, perform standard operations, expression solver calculations, integration and statistical operations on one & two variable, factorials, combinations and permutations, as well as polar-rectangular;
• NBASE - Perform binary, octal, decimal and hexadecimal operations and conversions;
• SOLV - Calculate unknown variables using an equation;
• PROG - Create and use named programs in REAL or NBASE modes to automate simple or complex calculations. BASIC alike programming with input, print, end, labels, goto, gosub, if, logical conditions, wait, rem, statistical commands,

There are three ways to calculate an unknown variable concerning its SOLVER calculation methods:

• Expression solver - Uses substitution; 
• Integration - Uses Simpson rule;
• Solver functions - Uses Newton rule.

CASIO fx-5000F Scientific Calculator made in 1991

With 128 stored formulas ready to be used, this model was very popular among students and professionals at the time, and it is probably one of the best pocket calculators from the 80's.

I opened it to clean the case and keyboard.

General parts view.

The Printed Circuit Assembly.

IC's:
- Hitachi HD62001A04 1G 33 processor (1991)
- OKI M5268V-H1  1716 controller
- Hitachi HD61914C 1G 43 1KByte SRAM  (1991)

The HD62001 processor is used in several Casio and OEM calculators only changing the firmware, for example:
- Casio fx-3900P: HD62001A01  6L 13
- Radio Shack EC-4023: HD62001A04 (OEM of fx-5000F)

Rubber keyboard painted keys.

Keyboard  membrane over the rubber keyboard, PCA side view.
 

 Keyboard  membrane, keyboard rubber keys side view.

PCA installed over the keyboard membrane.
Note the shielding/grounding spring at the top center.

 

Inner frame latches, at the display side.
 

Power switch in its bed at the inner frame.

Inner frame in place over the PCA.
Six self tap screws fix it in place.
Note the shielding/grounding spring at top center. Care is required to inset it in inner frame pass thru hole, while keeping the power switch in the correct position. 

2 x CR2032 batteries for a total of 6Volt are required to power this unit.

Full contrast on to show all the LCD pixels and annunciators.

This is a beautiful and feature rich calculator.
Forensic test result: 9.0000156854