Kovac SM-818M

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Calculators: Handheld: Kovac 818M (aka SM-818M)


		Size (approx):	90mm x 156mm x 27mm (max) (w,h,d) Weight 270g including batteries, 186g without.
		Power:	6V DC using 4 x AA size internal rechargeable batteries. Also accepts adapter/charger (6V DC, centre negative) through a top side socket on the far right.
		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 with the brand name. A neutral plastic display filter is tilted and slightly inset but gives a bright, easy to view display. Just below the display a ridged area contains a small raised panel with a red LED. Yet another black printed metallic sticker surrounds the raised switch area. The keyboard has raised sections for each key and is surrounded by a patterned light grey plastic. The keys are medium travel with a metallic click.
		Display:	8 digit blue VFD with a ninth digit for negative and error indicators. The ninth digit is slightly shorter than the rest and only capable of displaying "E". A single red LED is used for memory indication.
		Features:	Four standard functions with percentages. Switch floating, and fixed two decimal digit and financial input. Switched automatic two-function accumulating memory. Semi RPN logic.
		Age:	1973
		Manufacturer:	Made in Japan, serial number 0506414
		Comments:	Well built calculator similar to the 858M which has more functions. The logic is let down by archaic RPN and limited memory and the pseudo fixed decimal bug but does have good recovery.

Components:	Main board: 1 x cpu: Rockwell 15330PC 7324 (date code week 24 of 1973), 42 pin staggered DIL , 0.6" width black ceramic with metal cap 1 x 8 digit plus "E" VFD unit: single tube round face 4 x transistors 8 x diodes 2 x capacitors 4 x rectifiers (?) KD-214S 3GG (July 1973) 10 x resistors 1 x variable resistor Power board (with additional piggy-back board): 2 x transistors 6 x diodes 5 x capacitors 2 x resistors 1 x transformer
Boards:	The main cpu board is fixed to the rear of the case by three metal clips. It is joined to the keyboard assembly(D-007279), attached to the front of the case, by 15 coloured wires. A third vertically mounted board sits above these with the power supply components.
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
	The logic is semi Reverse Polish Notation (RPN): to do 4-3 key in (4)(+)(3)(-)
	Overflow on the input of a number is suppressed, keying in a ninth digit is ignored
	There is automatic constant on multiply and divide only
	Negative numbers are flagged by a minus sign in the far left (ninth) digit thereby allowing full eight digit negative numbers.
	Overflow shows the result and "C" (or "E" if negative) in the far left (ninth) digit and is recoverable using (C)
	Divide by zero shows zero and "C" in the far left (ninth) digit and is recoverable using (C)
	The memory is an switched accumulation: switch the memory switch to "on" and all results of the equals keys are added to the memory
	Memory store is indicated by an isolated red LED
	You can switch between fully floating (AF), fixed two digit decimal (2) and financial input (1/100) modes. The latter causes (2)(3)(4) to register as "2.34".
	Overflow in memory stores the result to the most significant eight digits
	It suffers the pseudo fixed decimal bug: in AF mode try (1)(+)(.)(0)(0)(0)(+) to give "1.000" which remains a fixed three digit decimal number until you use multiply or divide or need more digits

This image shows the front removed. The large main board sits in the rear of the case. Above the display you can the vertically mounted power supply board, which again has its own piggy-back board. The Rockwell IC is mounted on the underside of the board with a square hole cut out to reveal the top. Odd as this sort of early attempt at surface mounting was not really needed given the thickness of the case. The rechargeable batteries are inserted either side the grey compartment.

Compare it with the inside of the late Kovac 858M calculator.