Prinztronic MP300

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Calculators: Handheld: Prinztronic MP300 π (pi)

		Size (approx):	72mm(max) x 123mm x 20mm(max) (w,h,d) Weight 102g excluding batteries
		Power:	3V DC, 2 x AA size batteries. It accepts an adapter/charger (3V 100ma 3.5mm plug centre positive) through a socket on the bottom side on the far right.
		Case:	Made from a two-piece gloss finish dark grey and beige plastic case with rounded edges and corners. There is an oversized green display filter that gives a bright display. It contains a small metallic label that is printed black and blue with the company and model name and sits in its own recess. A brushed aluminium keyboard surround has the “on” label printed in black. The keys are small and squishy but work well.
		Display:	8 digit green VFD, with a ninth digit for negative, memory and error indication.
		Features:	Standard four functions with percentages, change sign, square root, pi and three function memory.
		Age:	1976
		Manufacturer:	Undefined manufacturer, made in Japan, with no detectable serial number
		Comments:	Compact calculator that is nice to hold with its smoothed edges. The logic is sound but the lack of recovery, missing constants and zero result for negative square roots could be better. The original case is soft black plastic with open top and half-moon cut-outs. Very similar to the Detson 803PM.

Components:	1 x cpu: NEC µPD278C H5Y986, 28 pin DIL, 0.6" width 1 x 9 digit VFD unit: single tube round front 1 x transistor 5 x diodes 7 x capacitors 7 x resistors 2 x resistor arrays 1 x transformer
Boards:	The keyboard assembly (GICO GK171-5 51.3.29) (date code 29 March 1976) sits loose on top of the main cpu board and is connected via 15-way ribbon cable. The whole assembly sits loose in the calculator.
Construction:	It is very difficult to prize apart the case that is held together by internal lugs only. You need to push the rear section sides in to pop the lugs but damage is very likely so I would not recommend it. Eventually the front can be lifted off.

Logic comments:	(C/CE) is used to once cancel the last number entered and a second time to clear the whole calculator.
	There is automatic constant on multiply and divide only
	Input overflow is suppressed, inputting a ninth digit is ignored
	Negative numbers are shown with a "-" in the far left (ninth) digit thereby allowing full eight-digit negative numbers
	Divide by zero shows "C” in the far left (ninth) digit and is not recoverable
	Overflow shows the result with "C" (or “E” if negative) in the left most (ninth) digit and is not recoverable
	The change sign can be used in mid-number entry
	Memory store is indicated by the decimal point of the far left (ninth) digit
	The (MRC) key is used once to recall the memory and a second time to clear it
	Overflow in memory is flagged as above and retains the original entry
	Negative square roots are not allowed and result in “C” with zero result

This scan shows the front of the case removed and the keyboard assembly hinged out of the way.

Quite a compact assembly with the tall components bent over. As the display tube has no mounting brackets or guides it can easily sit at an angle as the tension created by the connecting wires is considerable.

Compare with the Prinztronic P200.

Its worth looking a little closer at the logo plate (it is not very clear on the above image) as this is one of the few calculators to use the Greek alphabet. In fact the only other ones I can think of are the Tablulex series.