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Wang LOCI Printer

Updated 2/24/2002

Exhibited here is a Wang LOCI Printer. The LOCI printer is a peripheral device designed to connect to a properly-optioned Wang LOCI-2 calculator, providing hardcopy output capabilities for the calculator.

The Model/Serial Tag on the LOCI Printer

The LOCI Printer exhibited here was manufactured in the late part of 1966, based on date code information on some of the components in the machine. It is intended to be connected to a LOCI-2 calculator equipped with the "Option D" Input/Output interface. The I/O interface for the LOCI-2 calculator occupies an option slot in the calculator that provides a generalized Input/Output bus structure for connection of peripheral devices.

Inside the LOCI Printer

The LOCI Printer is built in a very modular fashion, with three main assemblies making up the device.

The 'MODUPRINT' Printer Module

The first component is the printer module. The printer is contained in a drawer that pulls out of the main cabinet, to allow paper and ribbon changes. At the back of the printer module is a circuit board edge connector that mates with a socket inside the main chassis. This design assures that when the drawer is pulled out, power is removed from the printer module.

ID Tag on the Printer Module

The printer module is a Model B3-9 printer, manufactured for Wang by a company called Practical Automation, Inc., located (at the time) in Shelton, Connecticut. This company is still in business making specialized printing devices, however, over the years, the company has changed onwership a number of times. A query sent via EMail to the company resulted in a kind response back saying that the information on this old printer has long-since been lost through ownership changes and moves.

The mechanism by which the machine prints is quite interesting. For a long time, I couldn't tell how this device printed, but thanks to a kind visitor to the museum, Mr. Charles Levinski, the mystery is exposed. Mr. Levinski is the sales/product manager for a company named "HECON". This company is a long-time manufacturer of specialized ticket and document printers (among other equipment), and a competitor of Practical Automation in the ticket printer market.

The technology is called "Modular Printing". The principle is quite simple. Each column to be printed is served by a print module. Each module contains a wheel that has raised characters (digits, symbols) around its circumference. The wheel also as gear-like teeth that are engaged via an escapement mechanism to allow the wheel to be turned a character at a time when activated by a small solenoid. Along with each wheel there is a set of contacts that encode the position of the wheel, to allow the driving electronics to know when the print wheel is in the proper position for the selected digit or symbol to print. As many of these modules are assembled together for the number of columns needed to be printed. In the case of the LOCI Printer, there are twelve modules, one for each column. The modules are arranged so that a sizable solenoid can push the print wheels up against the paper (with a ribbon interposed between the embossed symbols on the print wheel and the paper) so that the symbols are printed. The act of the large solenoid releasing causes the ribbon and paper to advance.

The modular printer in the LOCI Printer can print up to 11 columns of digits (one position for the floating decimal, and ten digit positions), and one column of special characters (sign). The print solenoid is quite powerful, and emits a fairly loud 'thunk' when the actual printing occurs. The individual module printwheel advance solenoids are quite quiet, emitting only a clicking noise as they advance the print wheels. The paper exits the printer module through a slot at the front of the printer. According to the tag on the printer, it runs from a 24 Volt DC power supply, and requires up to 1.6 Amps of current.

The Logic Card-Cage of the LOCI Printer

The next major component of the LOCI printer is the printer logic chassis. The all-transistor logic that controls the printer is located in a chassis of its own down the left side of the printer chassis. A total of fourteen small circuit boards make up the logic that drives the printer and provides interfacing to the I/O interface in the LOCI calculator.

Some of the LOCI Printer's Logic Circuit Boards

Some of these circuit boards appear to be some form of standard logic modules, such as one card which appears to have six three-input logic gates, and another that has eight two-input gates. These "standardized" logic modules are based on Wang's "Logi-Bloc" products, used in Wang's custom process-control and numerical-control system designs. The circuit boards are made of fiberglass, and have traces on both sides of the board, with plated through holes. Each board has thirty edge-connector contacts for bringing power and logic signals into and out of the board. The boards plug into a hand-wired backplane using Wang's tried and true square pin and clip interconnect technology, used extensively in Wang's early electronic devices. As with the LOCI-2 itself, the majority of the transistors in the logic are RCA-made 2N404 devices. One circuit board has two 2N1540 power transistors which are likely used to drive the paper advance solenoid.

The Backplane and Power Supply Wiring

The last section of the printer system is the power supply, simple affair made up of two small power transformers, diode recitifers, and filtering capacitors. The voltage supplies do not appeard to be regulated, rather, they are simply set in-situ to deliver the proper voltages, using a tapped wire-wound power resistor.

Operation of the printer is as simple as can be. Simply plug the printer into AC power, plug the cable between the back of the printer and the LOCI-2's "PRINTER" port, and turn on the power to the printer. A single power switch occupies the front panel of the printer, accompanied by a yellow-jewled pilot light to indicate when the power is turned on. The rear panel of the printer contains a fuse holder, the power cord, and a single 50-pin female "Centronics-style" connector to plug in the cable to connect the printer to the LOCI-2 calculator. The calculator has a matching female 50-pin connector on it's back panel that is marked "OUTPUT".

To advance the paper, either it can simply be pulled out manually, or the printer can be commanded to do so from the calculator, by pressing the "CAR'GE RET" key on the Option D-equipped LOCI-2 keyboard (or through a program via operation code 75). To print the content of the LOCI-2's display, the "WRITE" (operation code 11) key is pressed. The printer can print about 1 line per second, give or take a little.


Thanks to Sarah Hafner for the opportunity to acquire this wonderful artifact.
Thanks to Charles Levinski for the information on modular printer technology
Text and images Copyright ©1997-2011, Rick Bensene.