|
TCD Siemens T-56 Circuit diagram →
Fault finding
- this page is a stub
This page contains a collection of notes and suggestions that may be of help
when testing or reparing a
Siemens T-56 teleprinter connection device (TCD).
In the original German operating instructions, it is known as
Fernschreib-Endsatz (teleprinter terminating unit) or
Fernschreib-anschlussgerät (FAG).
The English version is known as
Telegraph Terminal Repeater T56.
The text below is largely based on notes from German collector Heinz Blumberg,
edited in 2020 [1], complemented
by our own observations and experiences.
|
WARNING —
Plese note that the device carries live mains voltages of 240V or higher,
which can be potentially lethal. Also note that the internal DC voltages
of 75V or higher, can be potentially dangerous. The use of an isolation
transformer is recommended.
Always disconnect the device from the mains before opening the cover.
Open the device ONLY when you know exactly what you are doing.
Before powering the device up, it is advised to do a visual inspection first.
In devices of this age, materials may have been used that become brittle
over time. This is especially the case with the mains power cable.
Check the power cable for hairline cracks. If it has become brittle, or if
you are in doubt, replace the entire cable.
For the following inspections, use the image blow as a reference.
Move the mouse over the image to see the highlighted references
of relays etc.
|
|
Open the device by removing the four screws with red rings from the corners
of the bottom panel. Then remove the case shell. Check the device for
obvious faults, such as damaged cables, loose wires and missing (or removed)
parts. Check whether the armatures of the unshielded relays can be moved
freely. Also check the relays for bended or burned-in contacts.
|
|
Check whether the rotary dial runs unobstructed. Turn it clockwise all the
way (i.e. select the digit '0') and then release it. It should return smoothly
to its basic position in approx. 1 second.
|
|
Check the push-buttons at the bottom edge of the control panel. After releasing
a push-button, it should return smoothly to its basic position. If it doesn't,
check whether it needs to be cleaned. If necessary, apply a drop of oil.
Note that the rightmost push-button (Lin/Loc) is an on/off switch. It must
be pressed again before it returns to its basic position.
|
The device contains two polar relays, also known as latching
relays, both of which are shielded by a transparent cover.
They are socketed, and are located at the centre of the device.
Relay A (unknown type) is at the right.
Relay B (T.rls.46a) is at the left.
Confirm that they are both present.
The contact of Relay B must point towards the rear of the device,
but this is barely visible as the distance between the contacts is
just 0.04 mm. Do not attempt to repair or re-adjust these relays,
unless you know exactly what you are doing.
|
|
|
|
The device is internally configured by means of three shorting bridges.
The first one selects one of these two modes of operation:
|
- Automatic exchange (Telex)
In this mode, the rotary dial is used to connect to the desired party.
This is also known as automatic exchange.
In the original German manual it is known as
Teilnehmerwahlverfahren
or Telegrafie-Wahlvermittlung (TW), or simply Telex.
- Manually patched operation (HV)
In this mode, the user is connected to the desired party by intervention from
an operator. This is also known as manual exchange or operator assisted
exchange.
In the original German manual it is known as Handvermittlung (HV).
|
|
|
For HV (manually patched operation) the bridge should be closed. It is
implemented as a toggle switch
that is mounted on a sub-frame, just behind
the current meter. Set this switch to 'HV' for use on a manually patched
exchanges. In the same vein, set it to 'Telex'
for use on automatic (dial-up) exchanges.
In the circuit diagram the bridge is designated 'DDr' and looks like this:
The other two bridges should be installed whenever the device is used for one-way
traffic only. One bridge shorts out resistor Wi14b, whilst the other one is
formed by a resistor (Wi30) that is connected in parallel to capacitor C10ab.
Its value has to be determined empirically in the field.
Both wiring bridges are located in the
bottom section of the device, that
can be accessed by removing the sub-panel from the
bottom of the case.
This compartment contains the wiring of the three large electrolytic
capacitors at the centre of the device, and also the wiring of the switching
contacts of most relays. Check whether a resistor is soldered across the
legs of C10a. If it is present, cut it out and also remove the shorting
bridge from Wi14b.
➤ Consult the circuit diagram
|
|
The first test is carried out with no other equipment connected to the T-56,
except for a lamp that simulates the teleprinter's motor.
This can be a simple desk light. Do the following:
|
- Connect a lamp to the Fs power socket at the rear of the device.
This is the leftmost power socket when viewed from the rear.
- Connect the device to the mains.
The power indicator (lamp) at the control panel should light up.
- Press and release knob Fs Loc. This selects local operation.
Relays U, UH, H1 and H3 should be activated. 1
The lamp connected to the Fs power socket must light up.
The lamp inside the Fs Loc knob should light up.
- Press and release knob Fs Lin.
Relays U, UH, H1 and H3 should be released.
The lamp connected to the Fs power socket goes off.
The lamp inside the Fs Loc knob goes off.
|
-
Relay H3 controls the motor of the teleprinter.
|
|
We will now test the T-56 with a teleprinter in local mode.
First do a safety check of the teleprinter. Check for faulty cables etc.
Please note that these devices are old, so don't be put off by exploding
capacitors and smoke. Perform the test as follows:
|
- Connect the power cord of the teleprinter to the Fs power socket at the rear of the T-56. This is the leftmost power socket when viewed from the rear.
- Connect the line plug of the teleprinter to the socket marked Fs at the rear of the T-56. If the teleprinter does not have an ADoS (Walzenstecker), use a converter cable.
- Connect the T-56 to the mains. Note that the device is active as soon as the mains plug is inserted into the wall socket. At this point, the indicator lamp at the upper edge of the control panel should light up.
- Press and release knob Fs Loc. This actives Local operation.
Relays U, UH, H1 and H3 should be activated and the Fs power outlet will be powered. As a result, the motor of the teleprinter starts running, but the teleprinter itself should remain in rest. At this point, the lamp in the Fs Loc knob should light up. The teleprinter can now be used locally. Try typing a few words.
- Press and release knob Fs Lin. This terminates local operation.
Relays U, UH, H1 and H3 should be released and the teleprinter motor should stop. At this point, the Fs Loc lamp should be off.
|
We will now test the line current. This can be done with a teleprinter
connected to the device, but it is also possible to use a dummy
and a regular desk light.
The dummy behaves like a (passive) teleprinter, whilst the desk light
is used to simulate the teleprinter's motor. If you decide to use the
teleprinter instead of the dummy, you may skip the section on
how to create a dummy.
To perform a line test, you also need an external line current source.
This simulates the current of an active telegraph line.
Although there several possible current sources, we assume in the
text below that you are using the
Siemens Anschlussgerät 13 (AG-13) shown above.
Set the polarity switch (I/II) of the AG-13 to 'I' (upper position).
The line current may be taken from the banana sockets at the top left,
or from the a and c contacts of one of the ADoS sockets.
|
A dummy can be useful when testing line circuit, as it is much smaller
and less heavy than a real teleprinter. This is particularly the case
when testing or reparing a T-56 device. A dummy can simply be created
by wiring a spare ADoS plug (Walzenstecker) as
shown in the diagram below.
Connect a 200Ω/3W resistor between the c and w2 contacts of
the ADoS plug. This simulates the telegraph relay in the teleprinter's
reception circuit. Next connect a shorting bridge between contacts a
and b. This simulates the closed contact of the transmitting relay.
The teleprinter's motor can best be simulated with a simple desk light,
that is connected to the Fs power outlet at the rear of the T-56.
It lights up when the T-56 activates the teleprinter motor.
|
|
To perform a line test, do the following:
|
- Connect the power cable of the teleprinter (or the desk light) to the Fs power socket of the T-56. This is the leftmost mains socket when viewed from the rear.
- Connect the line plug of the teleprinter to the Fs socket at the rear of the T-56.
In case you are using the dummy, insert it in the Fs socket instead of the teleprinter.
- Apply power to the T-56 by inserting the power cord into the mains wall socket.
The power indicator at the control panel should light up.
- Apply a line current to the a1 (+) and b1 (-) wire terminals at the rear of the device.
A suitable line current can be supplied for example by Anschlussgerät 13 (AG-13), of which the polarity switch is set to 'I' (see above).
- There should now be a bias current of approx. +5mA.
The current meter on the T-56 should indicate a current in the blue region (i.e. right of the centre). At this point, all relays should be released and Polar Relay B should be in the mark-position (i.e. the contact towards the rear).
- Press and release knob AT.
This initiates a call and connects the T-56 to the line.
The line current should now be +40mA.
At this point, Relay C should be activated, whilst Polar Relay B is still at rest.
- Reverse the line current.
This is done by setting the polarity switch of the AG-13 to the 'II' position. The current should now be -40mA, which is equivalent to the '1' mark in the red region of the meter.
At this point, Relays H1, L and H3 (motor) should be active, and the external desk light should light up (or the teleprinter motor runs).
Also at this point, Polar Relay B should be in the space-position (i.e. with its contact pointing towards the front of the device). Note that it is difficult to see this, as the space between the contacts is just 0.04 mm. Indicator lamp AT should be lit.
- Reset the polarity of the line current.
This is done by setting the polarity switch of the AG-13 back to the 'I' position. (+40mA).
Relays H3 and L are released.
Motor stops (desk light goes off).
AT lamp goes off.
The current should now be +5mA (bias).
|
|
Below is a random selection of hints and tips when trying to repair
a broken T-56. In all cases, take safety precautions before you start,
and realise that some voltage inside the device are potentially lethal.
The tips below are categorised by the type of problems. If you have any
additions or suggestions for improvement, please do not hesitate to
contact us.
|
- Check fuse (0.160 mA slow).
- Check whether the mains AC voltage reaches the transformer.
- Check the secondary AC voltage of the transformer.
- Check the DC output voltages of the bridge rectifier.
- Voltage at C6 and C7 should be 60V DC.
|
- Check (and clean) the interruptor contact inside the rotary dial.
- In normal operation, check whether the interruptor contact of the rotary dial is shorted.
- If the rotary moves irregularly, apply a tiny drop of oil to the governor inside the dial mechanism.
|
- Contact problems with regular relays: treat with tuner spray, or pull a strip of regular paper between the contacts whilst applying pressure to the contacts and/or the armature.
- Do not open the polar relays and try to re-adjust them!
The coil of Polar Relay A should be marked /36, whilst Polar Relay B should be marked /1. These relays can only be adjusted with a special testing tool for polar relays.
|
|
When first using the T-56 it may be necessary to adjust the levels
of some internal circuits. This is done with the three adjustment
screws at the right edge of the control panel, assisted by the
current meter and the 4-position rotary selector below it.
The meter selector has four positions:
|
| | | German | English | Description |
| | S | Sender | Transmitter | Transmission circuit current |
| | E | Empfänger | Receiver | Reception circuit current |
| | JT | Impuls Telegrafie | 2-wire double-current | Null setting (in 2 Dr 
mode) |
| | Fs | Fernschreiber | Teleprinter | Line activity (default) |
|
|
For 4-wire double-current configurations,
adjustment goes as follows:
|
- Set MODE-selector to 4 Dr
- Connect to a transmitting 4-wire single current subscriber
- Set meter selector to 'S'
- Adjust 'Rn' so that the meter is a the neutral position ('0')
- Connect to a non-transmitting subscriber
- Adjust 'Rs' so that the meter is at -1 (red) (= -20mA)
- Set meter selector to 'E'
- Adjust 'Re' so that the meter is at -1 (red) (= -20mA)
- Set meter selector to 'Fs'
|
|
For use on 2-wire single-current subscriber lines,
adjustment goes as follows:
|
- Set MODE-selector to 2 Dr
- Adjustment of the currents is only possible at the exchange
|
|
For use on 2-wire double-current lines (impulse telegraphy),
adjustment goes as follows:
|
- Set MODE-selector to 2 Dr
- Set meter selector to 'JT'
- Adjust 'Rn' so that the meter is a the neutral position ('0')
- Connect to a non-transmitting subscriber
- Adjust 'Re' so that the meter is at -1 (red) (= -40mA)
|
|
The following people have contributed to this page:
|
- Heinz Blumberg
- Paul Reuvers
- Marc Simons
|
- Heinz Blumberg, T-56 Endgerät Fehlersuchanleitung
Version 1.1, 29 October 2020.
|
|
|
|
Any links shown in red are currently unavailable.
If you like the information on this website, why not make a donation?
© Crypto Museum. Created: Tuesday 03 September 2024. Last changed: Thursday, 12 September 2024 - 09:04 CET.
|
 |
|
|
