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Sony SOBAX ICC-2550W Programmable Electronic Calculator
This wonderful machine is a prime example of Sony's second generation of desktop electronic calculators. This second generation of calculators from Sony leveraged integrated circuit technology, versus the hybrid transistorized circuitry of first generation machines, such as the Sony SOBAX ICC-500W. The 2550 offered high-end functionality for the discriminating calculator buyer in the early 1970's. It provides the four functions plus square root, 253 step programmability, nine memory registers, offline program storage on magnetic cards, built-in printer interface, and of course, the extremely high quality that Sony was (and still is) known for.
A view with the display cover in place
The 2550 is very nicely put together, in classic Sony style. The base of the cabinet is a heavy plastic casting, and the upper half of the cabinet is a combination of plastic mated with a rather beefy aluminum casting that serves as the keyboard/display panel. The upper section of the case is removable by taking out two screws, sliding the upper section of the cabinet toward the rear of the machine slightly, and lifting it off. A removable hinged cover is provided that covers the display panel, providing both protection, and a more aesthetic look for the machine when it is not in use. The back panel of the machine has connections for the power cord, a switched auxilliary power outlet (for providing power to an external device, such as the optional printer), and a port for plugging in an external printer.
Profile view of the Sony Sobax 2550.
The Sobax ICC-2550W is a 15-digit
programmable desktop calculator. Fifteen digits is an unusual number for
the capacity of a calculator -- most machines use sixteen or fourteen.
The reason for this is that the machine actually calculates results to
16 digits, but the 16th digit is a hidden gaurd digit, used for round-off
functions and improved accuracy. The display panel houses the fifteen
individual Nixie tube displays, along with 36 discrete
incandescent lamps for showing the status of programming functions, sign,
and error conditions. The calculator operates conventionally for calculators
of the time, with addition and subtraction working arithmetically, and
multiplication and division using algebraic entry, with an "=" key to
calculate the result for such operations. Decimal point location is fixed,
and set manually by the user using two keys that move the decimal point to the
left or right. A "CHG SIGN" key toggles the sign of the number currently
in the display, allowing the calculator to properly handle mixed-sign
operations. The 2550 has 9 memory registers, numbered 1 through 9, that can
be stored into ("M IN"), recalled from ("M OUT"), and cleared ("M CLR").
The memory register to be operated on is specified by a single digit keypress
following the memory function key. Memory registers can also be added to or
subtracted from by pressing the "M" key, followed by a memory register number,
followed by the "+" or "-" key. The "R" key swaps operands on the standard
four functions, for example:
The 2250 with the top part of the cabinet removed
This 2550 was built in early 1970, based on date coding on the early IC's in the machine. All 197 of the IC's that make up most of the logic of the 2550 are made by Sony, and all appear to be small-scale devices, with at most a few gates or a flip-flop or two in each package. The logic supply for the IC's is 4 volts, which makes it difficult to tell what kind of logic is used. It definitely isn't conventional DTL or TTL logic, the voltages are too low, but it seems likely that the logic is similar in design to DTL or TTL, just using slightly lower logic levels. The IC's are all 14-pin devices, with power supply provided on Pin 14 (+4V), and Pin 13 (Ground), a very unusual power supply pinout. All the IC's are dual-inline packages (DIP) in plastic cases, and have Sony 500-series numbers, IE: 501, 503, etc. The calculator also uses a large number of discrete components, mostly diodes and resistors.
The six circuit boards of the Sony Sobax 2550 (shown rear to front)
The electronics of the calculator are interconnected via a printed circuit board
backplane that contains some circuitry related to keyboard
encoding and signal conditioning. The rest of the backplane board holds
edge-card connectors mounted at an angle to accept the six plug-in circuit
boards the contain the main logic of the calculator.
Side View of Sony Sobax 2550 Internals The card cage that
holds the plug-in boards is made of heavy cast and machined aluminum side
rails, and has stamped sheet-metal covers that shield the top and bottom
sides of the cage to prevent EMI (electro-magnetic interference) from
radiating out of the machine. The circuit cards themselves are made of a
phenolic material, and have circuit traces on both sides, with plated-through
holes to provide connections between the sides of the board. One of the boards
has high enough density that there simply wasn't enough room for
traces to make all of the connections, so this board has a number of
hand-added jumper wires on the component side of the board to provide
the extra interconnections. Many of the circuit boards also have hand-wired
modifications made to them, such as a diode or transistor
tacked on to either side of the board. In general, it is much less
expensive to hand-add such engineering changes rather than make circuit board
design changes. Changes to circuit boards are usually 'saved up' until a new
production run is needed, then revisions were made to the circuit board
artwork and component layouts, and a new production run made with the
engineering changes incorporated.
The Delay Line Module The rear-most board in the card-cage
contains the circuitry for driving the acoustic delay line that serves as
the working storage for the machine. This card has comparatively few
IC's on it, relying mostly on discrete components to shape, condition,
time, and drive the bits going into the delay line, along with providing
conditioning, re-timing, and level shifting for the bits coming out.
The delay line is mounted to the back-side of the controller circuit card,
and is about the same size as the card itself. This is by far the most
complex and sophisticated delay line I've come across thus far. Given that
the 2550 has nine memory registers and 253 steps of program storage, and
also given that the machine has no signs of other on line storage such as
magnetic core, the delay line module must provide most all of the operating
storage for the machine. The delay line in the 2550 has far more capacity
than those in other machines
in the museum that use the same technology for working register storage.
It is interesting to note that the delay line has a label on it saying
"UNREPAIRABLE! REPLACEMENT AT SONY SERVICE CENTER ONLY". With as many
bits as have to be crammed into the loop of wire making up the delay line, the
adjustments to the timing circuitry to drive it must be very critical,
which explains why this device was not serviceable in the field.
A view of the back panel of the Sony ICC-2550W The 2550 provides a reasonable set of
programming functionality. The green keys on the keyboard designate
the program functions. The main mode of the calculator is set by two
keys that are mechanically linked so that only one can be depressed at any
time. These keys are labelled "MANUAL" and "AUTO". When the machine is
in "MANUAL" mode, it acts like a regular calculator, with no programmer
functions. When the mode is in "AUTO", then the calculator activates the
programmer functions. Three more keys under a lid to protect them from
accidental activation control the programming mode of the machine.
Two of these keys are mechanically linked so that only one can be depressed
at any time, are "PROGRAM" and "CHECK". When "PROGRAM" is depressed, and
the calcualtor is in "AUTO" mode, keypresses are stored in program memory.
This mode is used for entering programs. When "CHECK" is depressed, the
steps of the program can be verified step at a time, via indicators on the
display panel of the machine that light up for each key that is stored in
program memory. This mode can be used to 'debug' programs. Last of the
three program mode keys is a "CORR" key, a momentary contact switch
that is used to allow program instructions to be 'edited' by replacing a
program step with a different instruction. During program entry and
debugging, each step of the stored program is displayed via incandescent
indicators of the display panel of the machine. An indicator exists for
each key on the keyboard, and as each keycode in program memory is
encountered, the corresponding indicator lights up. This method of
indicating program steps is similar to that of the
Burroughs C3660.
Other green keys on the keyboard provide the ability to program
direct and indirect branches, conditionals, and other programmed functions
such as marking the end of a program and control of the optional printer.
Lastly, the green "S" key acts as a toggle for starting/stopping execution
of the program stored in memory.
The controls for the built-in
magnetic card reader are located on the right-hand side of the
keyboard. A group of three keys, mechanically linked so that only
one can be depressed at any given time, control the mode of the card
reader, providing "ENTER", "VERIFY", and "RECORD" functions. The card
reader cycles by itself when a card is inserted in the slot at the
lower right edge of the keyboard, drawing the card in, then ejecting
it back out the way it came. When in "ENTER" mode, the program stored
on the card is read into program memory. When in "VERIFY" mode, the
content of the card is compared with that in program memory, and if a
discrepancy exists, and "ERROR" condition is generated. Lastly, when the
card reader is in "RECORD" mode, the program memory is written out to the
card.
