Casio J-10

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Calculators: Handheld: Casio J-10

		Size (approx):	100mm x 164mm x 30mm (max) (w,h,d) Weight 192g excluding batteries
		Power:	3V DC, 2 x AA size batteries. It accepts an adapter (3V DC 0.25W, type AD-2S) through socket on top side to the far left.
		Case:	Large slightly wedge shaped case made from two pieces of mixed matt and gloss black plastic. The raised and tilted display area has a neutral plastic filter, framed in black. On this is printed white text for the brand and model number with a border. The brushed aluminium keyboard surround is printed black and silver with reversed out text for the switch labels. The large keys are squashy with a return click and individual key escutcheons, typical of Casio.
		Display:	8 digit blue VFD with no ninth digit (even though it exists)
		Features:	Standard four functions with percentage, square root, change sign and three function memory. Switched decimal point and rounding mode.
		Age:	c1984. A sales sticker on the back states W H Smiths £15.95
		Manufacturer:	Casio Computer Co., Ltd., made in Japan, serial number (or part number?) 5P002A printed on the battery compartment cover.
		Comments:	More at home on the desk this big chunky calculator just fits in the hand. The original case is soft black plastic with and open top and cut-outs either side. It has Casio embossed on the front and Made in Japan on the back. Whilst there are no obvious bugs the calculator is let down by seven digit negative number, lack of recovery and missing memory clear function – its very easy to forget that the (AC) clears it and the data is lost. There is another in this range called the Casio J-20. I have carefully lifted the sticker label on the rear of mine to find that underneath is the text for the model J-20, so this was a generic case.

Components:	1x cpu: NEC D1877C 8436P9, 28 pin DIL, 0.6" width black plastic 1 x 8 digit VFD: single tube flat face: FIP 9A5B No.4-8 21 1 x transistor 7 x diodes 11 x capacitors 3 x resistors 1 x transformer: TDK TC-12 4X
Boards:	The main cpu board (G861-1 A36266-1) is held by a screw to the rear of the case and joined to the front-fixed keyboard assembly via a 22-way ribbon cable.
Construction:	To open the calculator remove the two screws from the rear. This does not really help as the case is held together by internal lugs. The easiest way I found was to lever out the rear at the side edge and pop the lug. After popping the side lugs, hinge from the bottom. Be very careful as damage can easily result. Eventually the front will lift off.

Logic comments:	(C) is used to cancel the last number entered and (AC) to clear the whole calculator.
	Input overflow is suppressed, inputting a ninth digit is ignored
	Negative numbers are represented by a “-“ to the immediate left of the number but as there is no ninth digit you are limited to seven digit negative numbers
	There is automatic constant on multiply and divide but you have to hit a double operator to invoke it on add and subtract: i.e. (3)(+)(+)(6)(=) gives “9” then (=) gives “12” etc.
	Overflow shows the first seven digits (six if negative) of the result with the first digit showing “E” and is not recoverable.
	Divide by zero shows only “E.” in the far right (first) digit and is not recoverable.
	The change sign can be used in mid number entry but not on an eight-digit number when it is ignored. If you use change sign on a floating decimal number you lose the least significant digit.
	Square roots of negative numbers are allowed and result in a negative number
	There is a switch which changes the fixed decimal mode from 0 to 2 or 4 decimal places Another switch selects between floating decimal [F], round down [CUT] and round up/down [5/4]
	Memory store is not indicated – you have to remember it
	(AC) will clear the memory, which is annoying, as you have to use this to clear an overflow – and hence lose your memory store

	The box measures 108mm by 180mm and is 40mm deep. It is therefore just big enough to accommodate the calculator in its case with manual and nothing much else. Of double tuck-end construction it is printed in blue and red. There is a banner stating the number of digits – but having a model called J-10 with 8 digits is a little confusing. In this image the number eight is hidden by the price sticker.		This image shows the calculator with the front removed, exposing the inside of the battery compartment and main cpu board. Quite a high component count for such a late date. Plenty of space inside for a nice big board and well separated components. The high number of link wires are also a surprise. You can just see the green ribbon cable at the bottom which connects to the keyboard assembly.