Commodore Minuteman MM3PM

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Calculators: Handheld: Commodore Minuteman MM3PM

		Size (approx):	75mm (max) x 105mm x 27mm (max) (w,h,d) Weight 152g including batteries
		Power:	6.0V DC, internal rechargeable battery. Accepts an adaptor/charger (6V DC 0.2A, 3.5mm centre positive) through a top side socket in the middle.
		Case:	Lovely palm-sized white matt two-piece plastic calculator. The upper area is dominated by a black painted metallic panel which is silver printed with switch label and raised CBM logo. A red, slightly tilted and raised plastic display filter gives a bright with slightly limited viewing angle. The keyboard is surrounded by a black plastic panel. The keys are squishy but positive enough. Sticking with the red white and blue key colour scheme this compact calculator just oozes quality.
		Display:	8 digit LED multi-point segments with bubble lens and ninth digit for negative, memory and overflow indication
		Features:	Four function plus percentages and two function memory
		Age:	1974
		Manufacturer:	CBM Business Machines Ltd., Made in UK. Serial No. 18267
		Comments:	The minuteman series was a great concept for sturdy handheld calculators. Though most had a flat LED display this model has the more limited bubble lens type. The logic is OK with good recovery but let down by the negative zero bug and pseudo fixed decimal bug. Original case is stiff brown plastic with flip over top and popper closing. The rear label has the item "Imperial" on it so there must have been a US version as well.

Components:	1 x cpu: (circular integral sign) Western Digital LC1552-B 7436 (date code week 36 of 1974), 40 pin DIL, 0.6" black plastic 2 x ICs: Texas SN74592A M7432 (week 32 of 1974) display drivers both 14 pin DIL, 0.3" width black plastic 1 x nine digit red LED display with individual bubble lens: National Semiconductor NSA 198 434 1 x transistor 3 x diodes 7 x resistors (one joined between the battery pack and adapter socket) 4 x capacitors 1 x transformer 2 x sealed rechargeable batteries (elongated AA-sized)
Boards:	Main CPU board (ART 300538A) is soldered to the keyboard assembly underneath by 13 wires. A 17-way ribbon connector joins to the display.
Construction:	Remove the two screws on the back and gently prize the calculator's rear away from the front, hinging from the bottom. The batteries are fixed to the rear but all the boards are attached to the front.

Logic comments:	(C) cancels an incorrect numerical entry, pressing a second time clears the calculator
	Input overflow is suppressed, keying in a ninth digit is ignored
	Negative numbers are shown with a "-" in the immediate left hand digit, travelling into the far left (ninth) digit thereby allowing full eight digit negative numbers
	There is automatic constant on all four functions which you are reminded about by the (=K) key
	Overflow shows the result and "C" in the far left (ninth) digit and is recoverable using (C). With a negative overflow you only get seven digits of teh result as the eight is used for the minus sign.
	Divide by zero shows "0." and "C" in the far left (ninth) digit and is recoverable using (C)
	The memory system on mine is not working but: (M+) will add to the memory whereas (MT) will recall the contents, a second press clearing the memory.
	Memory store is indicated by the top right hand vertical segment of the far left (ninth) digit
	It suffers the negative zero bug: key in (1)(-)(2)(=K) to give "-1" now (+)(1)(=K) will give "-0"
	It suffers the pseudo fixed decimal bug; key in (1)(+)(1)(.)(0)(0)(0)(=K) to give "2.000" which remains a three digit decimal number until more digits are required or you use divide/multiply

The scan of the inside with the back cover removed shows a remarkably dense layout dominated by the huge cpu IC. The batteries (removed) sit on the clear display ribbon cable connector.

The main assembly is held in place by two plastic lugs on either side.