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Calculators: Desktop: Casio F-1

(c) Emil Dudek 2011

Size (approx):

185mm x 240mm x 60(max)mm (w,h,d)
Weight 660g excluding cable and adaptor


3V DC using 2 x 1.5V D sized batteries.  It accepts an adaptor (AD-4160, 3V [or perhaps 6V] 2.8W, centre negative) through a socket on the top edge, to the far right.
Display: 12+symbol blue/green VFD: the symbols (to the far left) are used for memory, error and negative indication. 
Features: Standard four functions with selectable floating/fixed decimal modes, switched rounding modes, switched constant, four function memory, register exchange, percentages and delta percent, square root, change sign, entry count, hundreds entry and delete. Semi-RPN logic.
Age: 1978
Manufacturer: Casio Computer Company Ltd., made in Japan, serial number 5285062 (on a sticker in the battery compartment)


A sturdy, medium-sized desktop from the later 70s which has a few extra useful functions.  My example is not working so cannot comment on the logic.  I am mystified why a DC adaptor should need a bridge rectifier and large heat-sinked power transistor. Very similar to the Casio F-2.

Case and Design: Two-piece construction made from matt light cream plastic, which has organic/futuristic flowing lines.  A heavily inset and almost vertical green plastic display filter gives a bright and high contrast display.  An additional blue plastic plate sits proud in its own recess with silver printed lettering for the brand and model number.

Keys and Switches: The keys in orange, light grey, dark grey, olive and powder blue are rather randomly grouped and uneven in appearance.  They are medium travel with a soft clunk on pressing and return. A metallic panel sits in its own recess and is printed with black text for the switch labels.
Construction: Remove the two screws from the rear.  There are then two side lugs to be popped (by pushing in the front section) and two lugs on the top edge, that easily release by hinging.  The rear can then be hinged off to the left.  The inside area of the case has two moulded matrix tables for keyboard layouts labelled GX-3.6 and GX-5.
Boards: The whole calculator assembly is attached to the front section: the keyboard assembly by four screws and metal brackets, the main board, face down, by a single metal bracket. The two are joined by a 26-way ribbon cable. Main board reference A10V-A1 J2-E GCMK-19EHB.  There is an earthed metal screen panel on the rear of the case.
Components: 1 x cpu: Hitachi HS38401A 8J (date code September 1978)  36 pin DIL, 0.6" width black plastic
1 x 12 digit + symbol green VFD display, single tube flat glass face NEC FIP13A10/LD8214 8J (September 1978)
1 x bridge rectifier: Fuji NF113
3 x transistors (one with large heat sink)
14 x diodes
25 x capacitors
6 x resistors
1 x voltage converter unit: CT0604

Logic comments: The (C) key clears the last entry (i.e. it is a CE key) and (AC) clears the whole calculator
Input overflow is not suppressed, keying a thirteenth digit causes an overflow state which is cleared by using the (>) key
A double zero (00) keys makes entering hundreds (or hundredths in Add2 mode) easier
There is switched constant [K] on multiply and divide only
There is switched rounding modes [CUT, 5/4, UP] and switched floating or fixed decimal points (F, 6, 4, 2, 1, 0)
The [ADD2] mode is used for financial input, keying in (2)(3)(4) will result in the input of "2.34"
There is switched item count [ITEM] which counts the number of entries added or subtracted recalled with (RC ITEM)
The logic is semi Reverse Polish Notation (semi-RPN), to calculate 5-3 key in (5)(+=)(3)(-)
Negative numbers are shown with a minus sign in the far left symbol cluster thereby allowing full 12 digit negative numbers
The change sign key can be used in mid-number entry as well after after entry, but not before
The (>) key acts as a delete function, removing the last digit you keyed in
Overflow shows the result shifted and "E" in the far left symbol cluster and is recoverable using (>) or (C)
Divide by zero shows zero and "E" in the far left symbol cluster and is not recoverable
Negative square roots are not allowed and result in a negative answer with error flag and is recoverable using (>) or (C)
Memory store is indicated by an "M" in the far left symbol cluster
Overflow in memory is flagged with and "E" in the far left symbol cluster and "0." and is recoverable using (AC), the memory retains the original number
It suffers the "divide to negative zero, once" bug, with constant switched on key in (1)(+/-)(/)(1)(0)(=)(=)(=) etc until you reach "-0.", one more division, however, will correct it to "0.", showing the level of extra precision internally