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Calculators: Desktop: Prinztronic C40

(c) Emil Dudek 2011

Size (approx):

195mm x 234mm x 57(max)mm (w,h,d)
Weight 1515g including cable and plug


Mains (240V 50Hz, 3W) power only through a permanently fixed mains cable of considerable length.
Display: 8+1 digit green VFD the ninth digit (to the far right) is used for error and negative indication. 
Features: Standard four functions with switched floating/fixed decimal modes and switched constant. Semi-RPN logic. 
Age: 1972
Manufacturer: Prinztronic: Dixons International, made in Japan, serial No. D 2010730.


A sturdy, large desktop from the early 70s which has very basic functions.  The logic is poor with lack of recovery, no trailing zero suppression on divisions and several bugs. I also find it is not tilted enough for easy use. Looks to made by Sharp.

Case and Design: A two-piece calculator made from smooth dark blue base, smooth light blue upper section which produces a thin, wide, wedge shape.  The front section has numerous escutcheons and blue-printed, finely ridged inlayed sections. The brand and model number is a similarly raised section with silver painted edges and text. An upper ventilation grill allows for transformer cooling.  A green plastic display filter sits inset at a slight angle and has white printed text for the eight numerals.

Keys and Switches: The keys in light blue and white are long travel with a chunky hollow-sounding clunk on pressing and return.  The switches are located in an inlayed area with white printed raised text labels. The on/off switch is situated on the right hand side, nearly at the top.
Construction: Remove the four screws from the rear and the back will easily lift off - tilting to the right.  

Boards: The main board (PWBE1011CC EPA SHARP 011) sits face down.  It is held in place with a sturdy metal bracket. Another one is used to mount the display tubes. It is connected to the keyboard assembly through an edge connector and 15 coloured wires.  There is a small mains voltage smoothing board with the transformer.
Components: 1 x cpu: Hitachi HD3276P 2K (September 1972), 28 pin DIL, 0.6" width black plastic
3 x display drivers(?): Toshiba TM4352P T (unknown date code), 16 pin DIL, 0.3" width black plastic
1 x IC: Hitachi HD3253P 2J (October 1972), 16 pin DIL, 0.3" width black plastic
9 x 1 digit green VFD display individual tubes with eight segments (Itron DG10F1 EJ)
6 x transistors
1 x rectifier (SIRB-00)
12 x diodes
14 x capacitors
22 x resistors (three on the underside of the main board that look like design tweaks)
4 x resistor arrays
1 x fuse
On the voltage input board:
1 x fuse
4 x capacitors
1 x mains transformer (17V 2Z)
The metal keyboard assembly is earthed from the board, as is a metal panel on the rear of the case.

Logic comments: (C) is used to clear the calculator and there is no clear entry function
My example does not have clear-on-power up function, which may be a defect
Input overflow is suppressed: keying a ninth digit is ignored
Negative numbers are shown with a minus in the far right digit thereby allowing full eight digit negative numbers
The Constant function is switched in with the (K) switch and operates on multiple and divide only
There is a switch for 0/2 fixed decimal points or "F" for floating
The result of divisions does not have trailing zero suppression: (9)(/)(3)(+=) gives "3.0000000"
Divide by zero shows  "0.E" and is not recoverable
Overflow shows "0E" and is not recoverable
The logic is semi-Reverse Polish Notation RPN so to do 3-4 you input (3)(+=)(4)(-) that latter really being a (-=) key
It suffers the pseudo fixed decimal bug: (3)(+=)(2)(.)(0)(0)(0)(+=) gives "5.000" which remains a fixed digit number until division is used.
It suffers the divide to negative zero bug: (0)(+=)(1)(-) will give "-1", now repeatedly divide by ten to eventually give "-0.0000000"