Commodore 786D Blue

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Calculators: Handheld: Commodore 786D

		Size (approx):	65mm (max) x 137mm x 24mm (max) (w,h,d) Weight 78g excluding batteries
		Power:	9V DC, 1 x PP3 size battery. Also accepts an adapter (DC-620R or 505) through a socket on left side in the middle. Remove batteries before using adapter.
		Case:	Blue softly stippled two-piece plastic case with black smooth keyboard surround. Raised logo and brand name looks like it never had highlighting. Heavily inset flat red plastic display filter gives a bright image but limited in viewing angle. Bold button colour scheme works well with keys that are wobbly and squashy.
		Display:	8 digit red LED with bubble lens with no ninth digit
		Features:	4 function calculator with percentages and multi-key memory
		Age:	1977
		Manufacturer:	CBM. Made in England (assembled at best), serial number 111313.
		Comments:	Pretty bog-standard Commodore of its time but in the rarer blue rather than beige or black. Two sequence key press for memory saves the extra buttons. Made as cheaply as possible for an aggressive market at the time. The logic is poor, with extended overflow, loss of negative sign, no memory indication and lack of a constant function. This is a bit odd as the IC can support 8+1 display notation and extended memory functions as can be seen in the Commodore 797. I suspect this may have been a commemorative "red white and blue" edition for the UK Silver Jubilee. There appears to be another model 786D in brown and beige with an (EX) key instead of the (M) key.

Components:	1 x cpu Commodore 3D-98MT 4876 (week 48 of 1976) 22 pin DIL, 0.3" width black plastic 1 x eight digit bubble lens LED display unit
Boards:	The keyboard doubles as the main cpu board and is fixed to the front via three screws and three rivets. Ref 200 949 176 224 Made in Japan.
Construction:	From the rear, remove the two screws, gently push the lugs in their recesses and hinge the back off from the top.

Logic comments:	The (C/CE) button is used to clear last entry of a number press again to clear the whole calculator.
	Overflow on number input is suppressed, typing in a nine digit number ignores the ninth digit
	An overflow shows the result with no decimal point - and you can carry on calculating. Eventually after reaching 10⁷⁹ it resets to zero
	Divide by zero results in a "00000000" which is also recoverable by dividing by 1
	There is no constant on any function, but you can do squares with (3)(X)(=) to give "9"
	Memory usage is by two key presses, i.e. (=)(M) to store, (+)(M) or (-)(M) to accumulate or decrement. Clear is (0)(=)(M).
	There is no indication of memory store - you have to remember it.
	Negative numbers are flagged by a "-" sign in the immediate left digit but as there is non ninth digit you are limited to the display of seven digit negative numbers. However, this doesn't matter as you can still carry on calculating - but with no minus sign.
	The percentage key just divides by 100
	No bugs found

Once the rear of the case is removed you can see - well not much really. One board doubling as the cpu board and keyboard assembly, one IC and one display. About as minimalist as you can get - apart from National Semiconductor calculators dispensing with the IC package.

Notice the Made in Japan sticker, which makes a mockery of the case label stating made in the UK.

Also notice that the adapter socket is connected directly to the IC - use the wrong one and kaput!