RTF MR201

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Calculators: Handheld: RFT MR201


		Size (approx):	75mm x 150mm x 22mm (w,h,d) Weight 174g including internal batteries.
		Power:	6V DC, 4 x internal Ni-Cd batteries. Also accepts adapter/charger (undefined) through a socket on the top side to the far left. The socket is an odd rectangular three-pin configuration.
		Case:	Slab-shaped case with rounded corners made from two pieces of matt black plastic. The red plastic display filter is heavily tilted inwards . White printed text just below this gives the model number and switch labels as well as some design lines. The keys are soft touch with a soft click and have labels that are prone to wearing off.
		Display:	8 digit red LED with individual bubble lens and a ninth digit for overflow, error and negative indication, Small zero notation display
		Features:	Basic four function with switched constant, and switched floating/fixed decimal mode. Algebraic (semi RPN) input logic.
		Age:	c1978
		Manufacturer:	VEB (Volkseigener Betrieb) Röhrenwerk Mühlhausen, Im VEB Kombinat Mikroelektronik", GDR (German Democratic Republic - former Eastern Germany). Serial number 018151.
		Comments:	Quite stylish and sturdy design with interesting colour scheme and a very odd power adapter socket. The logic is a little archaic with no input suppression, no recovery and a negative zero bug. The original cover is soft black plastic with flip over top and front popper closing. For those that wish to power up their model without the original power adapter I found that applying 6V DC to the two outer terminals was successful. Looking from the front, the left hand pin is positive 6V, the right hand pin is ground, the middle pin needs no connection.

Components:	1 x cpu: Unknown symbol U821D K7 (tends to suggest 1977), 28 pin DIL, 0.6" width black plastic 2 x IC: D492D K8 (again suggests 1978), 15 pin DIL, 0.3" width, grey plastic 1 x 9 digit LED module with individual bubble lens: WF VKD30 K6 (ok maybe it's the K that is the year identifier!) 14 x transistors 9 x diodes 5 x capacitors 19 x resistors 2 x transformer 4 x Ni-Cd batteries: 10220 10038 1.2V 225mAh
Boards:	The main board (RFT 54069) is held face down over the keyboard assembly by two plastic clamps. The four large-sized metal cased batteries (rather like oversized button cells) are fixed to the front with a red plastic bracket screwed to the rear of the case. The two boards are joined by 21 long yellow wires.
Construction:	Quite difficult to open as it is held together by internal lugs only. The easiest way I found was to squeeze in the back section on one of the sides whilst levering out the front. The two halves will then gently separate being careful not to damage the wires.

Logic comments:	The (C/CE) key will cancel the last entry on the first press and clear the calculator on the second
	Input logic is arithmetic (semi RPN), to do 6-4 key in (6)(+=)(4)(-=)
	Input overflow is not suppressed, keying in a ninth digit causes and overflow with "C" displayed in the far left (ninth) digit and is not recoverable but you can carry on calculating
	Negative numbers are shown with a minus sign in the far left (ninth) digit thereby allowing full eight digit negative numbers
	An overflow shows the result and a small "L" in the far left (ninth) digit and is not recoverable
	Divide by zero shows zero and a small "L" in the far left (ninth) digit and is not recoverable
	There is switched constant [K] on multiply and divide only
	There is switched floating [F] mode or fixed [2/3] decimal digit modes
	The [L] switch is used to charge the internal batteries
	It suffers the divide to negative zero (once) bug: with [K] switched on key in (1)(-=)(÷)(1)(0)(+=)(+=)(+=) etc to eventually get "-0" when one more (+=) will give "0"

	This image shows the two halves of the case separated. On the right you can see the rear section with the four over-sized button cells (they are actually about 25mm diameter and 10mm thick) held in place by the red plastic holder. A screwed on piece of card insulated the batteries from the front side. The large power smoothing (blue electrolytic) capacitor gets its own two plastic grips to sit in place on the rear as well. You can see the two black plastic clamps either side of the main board - holding it in and the strange three-pin adapter socket at the top.
		This image shows the red LED display with the small zero notation which was common on 1974 era Casio and Sperry calculators. The idea was that any particular one of the seven segments could fail and you could still identify what the number was. The hazing effect is caused by the individual bubble lenses confusing the sensors in my digital camera.