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Calculators: Handheld: Chinon Executron 8M

(c) Emil Dudek 2011

(c) Emil Dudek 2011

Size (approx):

115mm x 210mm x 50mm(max)  (w,h,d)

Weight 374g excluding batteries

Power:

6V DC through 4 x C size batteries. It accepts an adaptor (undefined, though 3V centre negative worked fine) through a socket on the left side in line with the display.  The adaptor will charge Ni-Cd batteries and charge time is quoted as 12 hours, and charging will occur when switched off.

Case:

Three piece light grey (gloss), dark grey (gloss and patterned) and light grey (patterned) plastic case.  The upper area has a red and black printed metallic sticker set in its own recess with the logo and model name.  Below this an angled and inset neutral plastic display filter has black borders and white printed text for the numerals and indicator.  The keyboard surround is patterned light grey plastic with obvious drill holes in one corner of each key cluster.  A black printed aluminium panel surrounds the upper keys and switches and sits in its own recess.  Main keys with white text are long travel hollow sounding work-horses.  The upper keys are smaller with a distinct metallic spring noise and have recessed black printed metallic labels.

Display:

8 digit blue fluorescent display with an additional digit for memory, error and negative indication.

Features:

Four function with switched constant, percentages, square root, change sign and two function memory.

Age:

1974

Manufacturer:

Chinon. Made in Japan, Serial No. 088084 also 830157 and 83142

Comments

Large format (it has to be to hold four C (UM-2) cells) calculator.  There is at least one more (probably later) version of the 8M model where the upper keys are larger and the constant switch is missing.  The logic is quite sound and only let down by the lack of recovery.

Components: 1 x cpu: NEC ?PD277C (K46446) 28 pin DIL
1 x 9 digit NEC glass encapsulated VF display LD80
26 x resistors
9 x capacitors
8 x diodes
2 x transistors
Boards: One main component board, quite sparsely populated and most of the components devoted to the on-board charger.  Two additional boards for main button bank and upper button bank are mounted on the front. Main board number FNKC01 234G 76598 along with 240501 and the "SD" logo.  There appears to be a date stamp on the main board 3074, which is assumed to mean week 30 of 1974.
Construction: Opened via four screws, two of which are in the battery compartment. Tie wires between front and back boards are too short to fully open the sides.  Button mechanism is just two copper wires pushed together.

Logic comments: (CA) is used to cancel the last number entered whilst a second press is used to clear the whole calculator, rear instructions recommend two presses before any calculation starts
There is switched constant on multiply and divide only - and the first register is used for multiplication, the second for division
Input overflow is suppressed: keying a ninth digit is ignored
Negative numbers are shown with a "-" in the (ninth) far left digit thereby allowing full eight-digit negative numbers
Overflow shows the result with "C" (or "E" if negative) in the (ninth) far left digit and is not recoverable
Divide by zero shows zero and "C"  in the (ninth) far left digit and is not recoverable
The change sign function can be used in mid number entry or after but not before
Negative square roots shows zero and "C"  in the (ninth) far left digit and is not recoverable
Memory store is indicated by the decimal point in the (ninth) far left digit
(MI) will store a number and accumulate to the memory whilst (RM) will recall memory and (RM)(RM) will cancel the memory
Overflow in memory is flagged and retains the original number
No bugs found