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- wanted item
Schreibmax was a small printer that could be attached to an
instead of the light bulbs. It printed the text on a small paper strip.
Although the Schreibmax could theoretically be attached to any lamp-based
Enigma, it was intended for the Naval Enigma machine
The Schreibmax consists of two units: MZSE the actual printer that is mounted on
top of the Enigma machine, and MZSS, the external power supply unit (PSU).
Schreibmax printers are extremely rare and are only occasionally on display
in museums. The power supply unit is even rarer and is often missing or broken.
The printer is a small black qubic box, on a metal base plate, that can be
mounted on top of a Naval Enigma machine. Behind the top lid of the printer
is a 9mm paper reel that exits at the top right of the front panel.
The paper is running past a print-wheel and is driven by a
capstan in combination with a pressure roller.
Two keys are present at the bottom: one for
inserting a plus (+)
and one for an empty space.
Mounting the Schreibmax on top of the machine is not a straightforward task.
First of all, the light bulbs have to be removed as the printer attachment
has 26 pin-shaped contacts
that take over the function of the bulbs.
More importantly: the printer is attached to the machine instead of
the wooden top lid. For this reason, the printer can only be mounted on top
of a Naval Enigma machine, as it is the only model that allows the
wooden top lid to be removed.
In order to use the Schreibmax with the M4 Enigma the
4.5V battery has to be removed and the two pins of the external power socket
must be shorted. We have currently no idea how this was done in practice,
but we've done it here with a short test wire
with two crocodile clips.
The Schreibmax consists of a metal frame with the actual printer mounted
on top. The frame physically replaces the top lid of the wooden Enigma case.
For this reason, the wooden lid of the Naval machines was removable.
Before mounting the printer however, the 26 light bulbs of the Enigma must
and the lamp panel must be made permanently available to the printer.
This is why the top cover of the Naval Enigma machines consisted of two
halves and the parts that normally covers the lamp panel can be removed.
After the lamp panel is freed, the printer-frame is attached to the machine
instead of the wooden lid by sliding it onto the hinges.
The underside of the metal frame
contains 26 pin-shaped contacts
that mate with the 26 spring-loaded
lamp sockets of the Enigma's lamp panel, when lowering the printer.
Once in position, the frame is
held in place by two bolts at the front corners of the base plate.
A rectangular cut-out
in the base plate of the Screibmax leaves the cipher
wheels accessible, so that the basic setting of the machine can be altered
at any time. The printer-frame is slightly wider than the machine itself,
sticking out at the right. This is done to accomodate the large 30-pin socket
that connects the printer to the external power supply (PSU).
The Power Supply Unit (PSU) is a rather complex device which has puzzled
people for a long time. In 2010, our good friend Arthur Bauer  finally
managed to crack the mystery when he was restoring his old Schreibmax and
his newly acquired PSU.
The PSU supplies power to the printing device but also
protects the switches of the Enigma's keyboard against the sparks caused when
operating the solenoids inside the printer.
He reconstructed the circuit diagram as follows:
In this circuit diagram, the Enigma has been simplified somewhat. As we are
connecting the Schreibmax to the lamp panel, the actual path between the keys
and the lamp contacts goes through the ETW, the wheels, the UKW and back.
In order to keep the currents as low as possible, a relatively high voltage
(115V DC) is used for driving the solenoids. Nevertheless, the solenoids inside
the printer (yellow in the diagram) cause enough sparks to cause permanent
damage to the switch contacts of the Enigma. An this is where the extra
circuits inside the PSU come in.
Each solenoid has a 1K5 resistor (R) connected in parallel and a 1µF capacitor
(C) connected in a network. This so-called Snubber network 
suppresses the voltage transients when operating the solenoids and
effectively protects the contacts of the switches by 'killing' the sparks.
As the high-voltage 1µF capacitors used for the Snubber network are relatively
large, they could not be placed inside the printer itself and were mounted
inside the PSU instead. As a result, each individual key contact has to be
wired to the PSU separately. 27 of such snubber circuits are present:
26 for the letters of the alphabet and and extra one for the plus-character
(+) that is available on the printer itself.
All wiring between the printer (MZSE) and the PSU (MZSS) goes via the large
30-pin connector on the side of the Schreibmax. All wires of this connector
The drawing above shows the connector at the right of the printer, when looking
into the socket from the bottom.
Two index holes are present, in order to prevent the connector from being
inserted the wrong way around. Please note that this connector carries
220V AC which can be potentially dangerous. The pin-out of this connector
is shown in blue in the drawing above.
As there is not sufficient room inside the printer itself, the capacitors (C)
and resistors (R) are placed inside the PSU. This is the only reason why
we need so many wires between the printer and the PSU.
The image above shows the wiring diagram of the PSU. All resistors (R) are
wire-wound 1K5 types and all capacitors (C) are 1µF/1000V.
Capacitor (C1) is 375µF/200V.
Without the dedicated MZSS power supply, the printer can not be used.
In 2011 we had the unique opportunity to examine the only working Schreibmax that
we know of, at the Foundation for German Communication in Diemen (Netherlands)
The museum curator, Arthur Bauer, spend many hours getting his unit to work
and his efforts have really been paying off.
The image at the top of this page shows his Schreibmax on top of our
Enigma M4. The yellow plug sticking out at the right
is the connection with the external PSU.
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© Crypto Museum. Created: Monday 27 February 2012. Last changed: Tuesday, 15 September 2020 - 17:03 CET.