Kovac SM-858M

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Calculators: Handheld: Kovac 858M (aka SM-858M)


		Size (approx):	93mm x 161mm x 33mm (max) (w,h,d) Weight 196g excluding batteries.
		Power:	6V DC using 4 x AA size batteries. Also accepts adapter/charger (DC 6V undefined but centre negative) through a top side socket on the far right. Rear label states: "Nickel-Cadmium batteries will recharge even power [sic] switch is off. Full charge requires 12 hours. Avoid exsessive [sic] overcharge."
		Case:	Bulky calculator made from three pieces of light (gloss) and dark grey (patterned) plastic. A black printed metallic sticker sits in a raised recessed panel at the top. A smaller sticker sits below the display on top of the ridged design with the model number. A green plastic display filter is tilted and slightly inset but gives a bright, easy to view display. Yet another black printed metallic sticker surrounds the raised switch area. The keyboard has raised sections for each key.
		Display:	8 digit green VFD with a ninth digit for negative, memory and error indicators.
		Features:	Four standard functions with percentages, change sign, square root and three function memory. Switched constant and fixed decimal modes.
		Age:	c1974
		Manufacturer:	Made in Japan, serial number 845233
		Comments:	Well built calculator similar to the 818M which has less functions. Though bulky the logic is sound and only let down by the lack of recovery. The original case is soft black plastic with a top flap and front Velcro closing.

Components:	1 x cpu: NEC µPD277C K43106, 28 pin DIL , 0.6" width black plastic 1 x 9 digit VFD: single tube round face 2 x transistors 8 x diodes 8 x capacitors 26 x resistors 1 x transformer: Sumida 5424
Boards:	The main cpu board (260501) is fixed to the rear of the case by three metal clips. It is joined to the keyboard assembly(G-032373), attached to the front of the case, by 17 coloured wires.
Construction:	Remove the two screws at the rear. The front and rear sections then separate easily.

Logic comments:	The (C) key is used once to clear the last entry and a second time to clear the whole calculator
	Overflow on the input of a number is suppressed, typing in a ninth digit is ignored
	There is selectable constant for multiply and divide only by using the [K] switch
	Negative numbers are flagged by a minus sign in the far left (ninth) digit thereby allowing full eight digit negative numbers.
	The sign change function can be used in mid number entry
	Overflow shows the result and "C" (or "E" if negative) in the far left (ninth) digit and is not recoverable
	Divide by zero shows zero and "C" in the far left (ninth) digit and is not recoverable
	Negative square roots are not allowed and result in zero and "C" in the far left (ninth) digit and is not recoverable
	Store numbers in the memory by use of the (M=) key, recall and clear by using the (MRC) key
	Non-zero memory store is indicated by the decimal point of the far left (ninth) digit
	The percentage key just divides the current register by 100
	No bugs found


This image shows the front removed and the black felt light restrictor that surrounds the display tube. The case is oversized so the design uses a full sized board when it doesn't really need to. The batteries are inserted either side the grey compartment underneath. Compare it with the inside of the late Kovac 858M calculator.	The box measures 225mm x 135mm and is 47mm deep. This image shows the top which is a hinge off lid. Whilst it has no serial number on the front space there is a sticker on the side where again the words "serial number" are printed. There is a polystyrene tray inside to hold the calculator, cover and manual comfortably. Note that there is no mention of the Kovac brand name on the box at all.	The manual measures 104mm by 151mm and is 16 pages printed in dark brown throughout. Notice again the lack of any mention of the Kovac brand, and the brand label on the calculator is left blank. In English only it has quite a few examples. Printed in Japan.