Kings Point (Kingspoint) 8412 Micro Memory

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Calculators: Handheld: KingsPoint Micro Memory (aka 8412)


		Size (approx):	86mm x 155mm x 30-32mm (w,h,d) Weight 266g excluding batteries
		Power:	6.0V, 4 x AA size batteries. It accepts an adapter/charger (undefined, but supplied with calculator, centre positive) through a socket on the top side to the far right. Instructions on the rear state that when the Battery Low light is on recharge batteries for 15 hours and you may use the calculator whilst charging. The batteries are held in a removable cartridge but it doesn’t appear that this could be swapped for a battery pack; just insert four AA-sized rechargeable cells. It appears to be a needless expensive configuration.
		Case:	Square edged calculator made from two-piece patterned black plastic case. The majority of the upper section is covered in thick brushed aluminium panels that wrap over the edges. The top panel is printed with black text for the brand and AC adapter reminder information on the top edge. The neutral plastic display filter has printed white text for the digit numbers and four extra indicators. It is slight raised and very slight tilted. Another metal panel surrounds the keyboard but is painted black with reverse out text for the switches and model name. The keys are soft touch, short travel and slightly wobbly and the switches do not protrude much making them quite fiddly. Two large labels on the back give basic instructions and examples.
		Display:	8 digit blue VFD, with four additional red LEDs for overflow, memory, low battery and negative indication.
		Features:	4 function calculator with percentages and automatic two-function memory. Switch fixed decimal point capability. RPN logic.
		Age:	1974
		Manufacturer:	No information on the calculator but the case says “Japan”, no serial number either.
		Comments:	Very solidly built calculator with early display system. The original case is soft black plastic with top over flap and front popper closing. There are two smaller side top flaps and a black carry strap attached to the right hand side. The word Japan is embossed on the front. The logic is OK for such an early machine but the RPN system and pseudo decimal bug shows its age. My example has an unreliable decimal switch.

Components:	1 x cpu; Rockwell A1000PE(?) 15330 7403 (week 3 of 1974), 42 pin staggered DIL, 0.6" width 8 x 1 digit VFD tubes with four additional isolated red LEDs 13 x transistors 16 x diodes 1 x bridge rectifier: General Instruments 5W05 T325 4 x capacitors 27 x resistors 1 x variable resistor 3 x resistor arrays 1 x transformer
Boards:	The main cpu board (PC-P611) sits on top of the keyboard assembly and mounts on two metal brackets with screws. They are joined by a 24-way black plastic block connector, of which only 22 connections are used. The display assembly uses the metal board mounting bracket as the bracket to hold the display tubes.
Construction:	Remove the screw from the back and the second one from inside the battery compartment area. The back easily lifts off.

Logic comments:	The (C) button is used to clear the calculator whilst a second press will also clear the memory (just as the (CM) key does). There is no cancel entry function.
	Overflow on number input is suppressed inputting a ninth digit is ignored
	An overflow shows the result with the Overflow LED alight which is recoverable using (C).
	Divide by zero results in zero and the Overflow LED alight which is recoverable using (C)
	There is automatic constant on multiply and divide only
	Negative numbers are shown by the Negative LED alight thereby allowing full eight digit negative numbers.
	It operates Reverse Polish Notation which takes a little getting used to: to perform 3-4 key in (3)(+)(4)(-) to give"-1"
	The automatic memory is switched on using the (MR>ON) switch. From then on any result of equals is added to the memory.
	Memory store is indicated by a red LED alight.
	Battery low status is indicated by another red LED alight - therefore draining the battery even quicker!
	There is switched decimal mode: F for floating point, 4 and 2 for fixed four and two digit decimals and $ for financial input (i.e. pressing (4)(9)(9) in this mode inputs "4.99" )
	The calculator has the pseudo fixed decimal bug; key in (1)(+)(0.00000)(+) to give "1.00000" which stays until the calculation result requires more digits or you multiply or divide.

Main board

The scan on the left shows the extremely dense main cpu board. The whole assembly is dominated by the individual VFD tubes and the metal mounting bracket. Underneath the display is the main Rockwell IC and loads of transistors driving the digits. At the bottom you can see the black block connector, the keyboard side being two pins longer.

Notice at the top the large transformer and heat-sinks on the transistors and the unusual use of a bridge rectifier rather than four diodes for the VFD driver circuit.

Compare with the main board of the Kingspoint 8413.