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Racal MA-4233
Ruggedized thermal printer

The MA-4133 is a small military ruggedized thermal printer for use with message equipment, designed and built by Racal Datacom Ltd. (UK) in the late 1970s. It was designed especially for printing incoming messages on the Racal MA-4231 automatic morse receiver. The image below shows the rather rare MA-4233 printer, which is known as NSN 5865-99-539-6085.

The unit measures 232 x 170 x 63 mm, which is roughly twice the size of the decoder. It weights approx. 3 kg. Operating temperature range is between -10 and +55°C, whilst the storage range is between -40 and +70°C.

It is powered by an internal rechargeable battery that is charged from the external power supply. The power switch of the printer is on the left and is mounted in such a position that the unit is powered OFF automatically when the lid is closed. The internal NiCd battery can be charged by any 80 mA source in the 12-30V DC range.
Another close-up of the printer

Input is via ITA2 or ITA5 serial code at 5V logic level, with a data rate of 50, 75, 110, 300 or 600 baud. Latin characters are printed in a 7 x 5 dot matrix, but other languages (e.g. Arabic, Farsi, etc.) are printed in a 7 x 7 matrix. The Arabic version is called MA-4233A. The text is printed line-by-line upon receipt of a complete line, or when the unit is idle after receipt of a message. The MA-4233 can print up to 31 characters on a single line (including spaces) at 60 chars/s. This means it can print approx. 200 lines of text per minute. It takes 60 mm wide rolls of metallic electrosensitive paper, with an average length of 30 m.

The print with closed lid Another close-up of the printer The MA-4233 printer in operation Close-up of the printer Close-up of the power switch Power and data connectors
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The print with closed lid
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Another close-up of the printer
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The MA-4233 printer in operation
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Close-up of the printer
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Close-up of the power switch
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Power and data connectors

The MA-4233 printer has two 5-pin Fischer sockets at its right side. The leftmost one (female) is the serial data input. It is designed for a 1-on-1 connection with the Racal MA-4231 morse receiver.

Looking into the Fischer sockets
The pins of these sockets are numbered from 1 thru 5, but note that this numbering is different from the numbering inside the matching plug! The pins are wired according to the wiring diagram below. The colours specified in the table are the ones used in the original Racal cables.

Connection to the MA-4231 (left)

Pin Name Colour Description
1 n.c - No connection
2 DATA Red Serial data input, from MA-4231
3 READY White Printer ready (input)
4 Power Yellow Power supply or battery charger (+ 11 to 30V)
5 GND Green Common connection (ground)
Shield GND Braid Common connection (ground)

A suitable male connector for this socket is Fischer S103 A054-130+.

Connection of a battery charger (right)

Pin Name Colour Description
1 n.c - No connection
2 n.c - No connection
3 n.c - No connection
4 Power Yellow Power supply or battery charger (+ 11 to 30V)
5 GND Green Common connection (ground)
Shield GND Braid Common connection (ground)

A suitable female connector for this socket is Fischer S103 Z054-130+.

Power supply
The unit is powered by a set of internal rechargeable NiCd batteries that can be charged via any of the connections at the right. Please note that the batteries must be fully charged before the unit can be operated, even when an external voltage is supplied. Also note that the batteries in most of these surplus devices, are either dead or worn-out, even when the device (and in some cases the battery) looks brand new. These units were built around 1980 and its battery life time has long expired. Whithout a healthy battery, the unit can not be operated properly.

Inside the MA-4233 are two different batteries. One consists of 2 VARTA 12 V NiCd packs connected in series (24V total). The other battery is a 6V high-current battery. When these batteries start leaking, they may cause permanent damage to the PCB and the internal connectors.

The charging voltage is supplied to the same pins of the sockets on all devices of the MA-4230 family. These pins (4 and 5) are all interconnected, allowing a battery charger or external power supply to be connected anywhere in the chain. Generally though, a battery charger would be connected to the printer (if present). When connected to a suitable radio, power would generally be supplied by the radio (connected to the MA-4230 unit).

Please note that, when using an external power source for charging the batteries (e.g. power taken from a transceiver), the battery charger should be disconnected.

The MA-4233 is housed in a ruggedized die-cast aluminium case with a lid at the bottom. The lid is held in place by 6 hex-head bolts that are easily removed. All electronics are contained on a single PCB. Once the lid is removed, the solder side of the PCB is revealed.

The PCB covers the entire bottom section of the printer. By removing a couple of bolts at the bottom, the PCB can be removed. Three green connectors are used to connect the PCB to the thermal printer unit, the batteries, the power switch and the two Fischer connectors.

The batteries are mounted in the top section of the die-cast case. This is rather unfortunate, as old batteries are likely to leak their chemical substance onto the PCB, causing permanent damage. Two battery packs are present: one for the 6V and one for the 24V power supply.
DIP switch area

The images below show the interior of the MA-4233 and the layout of the PCB. The rightmost image shows how the PCB can be damaged by leaking batteries.

Batteries inside the MA-4233 printer 6V battery 24V battery PCB of the MA-4233 DIP switch area Close-up of the DIP switches Power supply detail Damage caused by leaking battery
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Batteries inside the MA-4233 printer
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6V battery
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24V battery
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PCB of the MA-4233
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DIP switch area
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Close-up of the DIP switches
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Power supply detail
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Damage caused by leaking battery

Connecting the printer to an MA-4231
The MA-4233 is a universal thermal printer, that can be connected to a wide variety of devices, including (portable) PCs and the MA-4231 automatic morse receiver. The printer has a standard RS-232 compatible serial port and can be configured for a wide range of baud rates.

Baud rate and word format can be configured with 6 DIP switches towards the edge of the PCB. Unfortunately, the PCB has to be removed before the settings of the DIP switch can be changed. The first four switches (1, 2, 3 and 4) are used for selection of the baud rate.

Switch 5 is used for selecting the word length (5 or 8 bits), whilst switch 6 is used for selecting the number of stop bits. Unlike the MA-4231 morse decoder, the printer does not support parity. A table for setting the DIP switches is present on the inside of the bottom lid.
Close-up of the DIP switches

The table below shows how the DIP switches should be set for a particular baud rate. Please note that the top row of the blue DIP switch is marked with a + sign. The table shows the position of the notch on the row with the + sign, which is either up (U) or down (D). The DIP switches in the above image are set up for 1200 baud 8N1.

  1. Technical Manual MA.4230 MA.4230S Morse Encoder (with Battery Charger MA.4232)
    Racal-Datacom Limited. 1 October 1980, issue 1.10.80-100.

  2. Technical Manual MA.4231 Automatic Morse Receiver
    Racal-Datacom Limited. 2 February 1980, issue 2.2.80-100.

  3. Conversion notes for the Racal MA4230/4231
    John's Radio, Conversion from Arabic to English. Date unknown.
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Crypto Museum. Created: Thursday 26 August 2010. Last changed: Saturday, 01 July 2017 - 11:12 CET.
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