Prinztronic M Type II

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Calculators: Handheld: Prinztronic M (type II)


		Size (approx):	54mm x 120mm x 16mm (max) (w x h x d) Weight 64g not including batteries.
		Power:	6.0V DC using 4 x AAA size batteries. It does not accept an adapter.
		Case:	The brick-shaped compact case is made of three-piece smooth plastic design. The lower section is buff, the upper dark brown and the keyboard surround buff. A flat and flush red display filter gives a clear if limited angle of view image. The filter has the make and model number printed in white text. They keys are clear plastic with labels underneath. They are short travel, positive click and quite loose – the whole thing rattles like a box of matches.
		Display:	8 digit red LED with bubble lens with a ninth digit for negative and error indicators. Additionally there is a isolated red LED just below the eighth digit for memory indication.
		Features:	Standard four functions with percentages and switched memory accumulation
		Age:	1974
		Manufacturer:	No manufacturing details except made in Hong Kong. The serial number is 232973 on a sticker on the battery compartment cover.
		Comments:	Lovely to hold, these compact, Dixons sold calculators were a major break through in price at the time. The logic is reasonable with good recovery but let down by the pseudo fixed decimal bug and archaic memory system. The original cover is soft black plastic skin-effect with a top flap that tucks in a front pocket.

Components:	1 x cpu, 28 pin DIL, 0.6" width, black plastic 1 x IC: display diver, 20 pin DIL, 0.6" width, ceramic package 1 x 9 digit LED unit with bubble lens 1 x red LED; in line lead type 1 (at least) x transistor ? x diodes ? x capacitors ? x resistors ? x resistor arrays 1 x transformer
Boards:	The display board (019A) sits above the full length keyboard assembly/main cpu board and is joined by: a ten-way plastic connecting block at the bottom and a eight-way connector at the top. The whole assembly sits lose in the front of the case and is soldered together so cannot easily be separated for examination.
Construction:	I do not recommend you try this one - it is very difficult. Gently push and twist a blunt stick on the right hand side looking from the rear. Inside the battery compartment you will just see a fixing lug. About 2cm from the top and the bottom there are others on this side. By the time these two are popped you can do the top and bottom lugs and finally the three on the other side.

Logic comments:	The (C) key is used to once cancel an entry whilst a second press clears the whole calculator
	Input overflow is suppressed as keying in a ninth digit is ignored
	Negative numbers are shown with a "-” to the immediate left of the number, travelling into the far left (ninth) digit, thereby allowing full eight digit negative numbers.
	There is automatic constant on all four functions
	Divide by zero just shows zero and “C” in the far left (ninth) digit and is recoverable using (C)
	Overflow shows the result and “C” (or “E” if negative) in the far left (ninth) digit and is recoverable using (C)
	There is indication of memory store by an individual red LED just below the digits
	Memory is switched accumulation: when (å) is on, all results of (=) are added to the memory
	Memory recall is by pressing (M) whilst memory clear is by pressing (M) a second time
	It suffers the pseudo fixed decimal bug: key in (1)(+)(0)(.)(0)(0)(0)(=) to give "1.000" which remains a three digit decimal number until more digits are needed or you use multiply/divide.

This image (left) shows the back removed (read notes above about opening) and clearly shows the display board sat on top of the main keyboard/cpu board.

This construction is typical of the "mini" series made as cheaply as possible. The big danger is leaking batteries damaging the (mostly) exposed main board.

Notice also the large number of spare holes in the display driver IC section, implying that this board was used for more than one model.

The sticky pad on the blue transformer is used to add pressure to the front area memory switch.

This image (left) shows the unit removed from the front section. Unusual shaped board letting the man display show through. You can just see the single point LED to the left below the display.

To the middle left are two metal areas that the memory switch connects together.