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Calculators: Handheld: Citizen 801D (type I)

Size (approx):

82mm x 136mm x 25mm  (w,h,d)
Weight 132g excluding batteries

Power: 6.0V DC with 4 x AA size batteries.  Accepts an adaptor/charger (CTZ-800R 6V DC 0.25W, centre negative) through a socket on the top side to the far right.  The on/off switch is on the top side, in the middle.
Case: Rounded two-piece smooth plastic case of light grey front and dark grey back.  A flat, flush , warp-around green plastic display filter gives a good clean image.  Just below this is a metallic sticker printed black with the brand and model number; which sits in its own recess.    Large front brushed aluminium panel is slightly inset just like many other GICO keyboards.  The subtle coloured keys are soft and squishy but work well enough.  
Display: 8 digit green VFD, with a ninth digit for minus, error and memory indicators
Features: 4 function calculator with percentages, change sign  and four function memory
Age: c1976
Manufacturer: Citizen Business Machines Inc., made in Japan.  Serial number 70103135.
Comments: Nice calculator with a bright clear display that is like some of the  Decimo Vatman series et al.  There were two models called 801D and this version appears to be the least common.  The logic is fine (except for the negative zero bug)  but the simple functions and lack of recovery let it down.  See the other Citizen 801D. The original case is soft black plastic with red stitching.  It is open topped with two cut-outs on the sides and Citizen embossed on the front.

Components: 1 x cpu: Matsushita M58618-83P 582E, 28 pin DIL 0.6" width
1 x 9 digit VFD single tube round face
2 x transistors
3 x diodes
6 x capacitors
8 x resistors
2 x resistor array
1 x transformer: DCT400 Zebra
Boards: The keyboard assembly (801DP 458618-83 GK251-34, GICO Japan) sits loosely on top of the main board and is joined by 11 wires.
Construction: Quite difficult as it is held together with poppers only.  Try using lolly' sticks to lever apart the sides where the two cut-outs are located.  Squeeze in the front section whilst levering the two sides apart.  Eventually the front section will lift off.

Logic comments: The (CE) key is used to clear last entry of a number and the (C) key clears the whole calculator.
Input overflow is suppressed, inputting a ninth digit is ignored
There is automatic constant on all four functions
Negative numbers are shown by a "-" in the far left (ninth) digit thereby allowing full eight digit negative numbers
The change sign function can be used in mid number entry
An overflow shows the result with a C (or E if negative) in the far left (ninth) digit and is not recoverable 
Divide by zero results in a tall "C in the far left (ninth) digit and is not recoverable.
Memory store is indicated by the decimal point of the far left (ninth) digit.
This calculator has the negative zero bug; try (1)(-)(2)(=) to give (-1), then (+1)(=) will give "-0"

This scan shows the front removed exposing the GICO keyboard assembly on top of the main board.  In this case the cpu IC is under the (%) key.

Very similar internal design to such calculators as the C.Itoh 8005 and Decimo Super Vatman X.