NOTE: Always give attention to any unusual sounds or odors coming from any of the electrical equipment. These may give an early warning of any cable damage or faults in the system.
If you suspect any faults in the system turn everything off immediately. A delay may result in more serious damage to other equipment.
Disconnect the power before attempting to remove anything in contact with the power supply!
If a fault is not easily identifiable from a physical inspection disconnect the stabilizer from the main console and check it without anything else connected.
Variacs and stabilizers should be kept well away from the master console because magnetic fields can cause audible hum. Single insulated wires and open terminals (see picture) should not be accessible (provide safety covers).
Disconnect (unplug) the stabilizer from the power before doing any other ‘disconnecting or connecting’.
Due to the high temperatures, dust, and humidity in Indonesia, faults in stabilizers are quite common.
Because of the high levels of protection provided in commercial language laboratory circuitry the fault is most likely to be in the electrical connections/ plugs/ sockets, wiring, or the stabilizer. An overload in the main console will usually cause the laboratory to shut down.
2(a). GENERAL PERFORMANCE CHECKS (Daily)
Audio Active (AA) Laboratories
Procedure
With the language laboratory master console turned-on:
- play a test tape in the master recorder and switch the sound so that it is being transferred to the student units (see operation manual for your particular laboratory)
- check the quality of sound coming from the master recorder
- go to each student unit and put on the headphones and listen carefully to the quality of the sound in both ear-pieces (check that the student volume is turned up). Rub your fingernail against the microphone. You should be able to hear the scratching sound clearly in both ear-pieces
- with the headphones still on, gently wriggle the cables, especially close to the plug and each ear-piece. If there is any crackling, or if the sound disappears you can usually repair the fault by cutting the cable near the break and re-terminating the cable (see soldering).
2(b). GENERAL PERFORMANCE CHECKS (Daily)
Audio Active Comparative (AAC) Laboratories
Procedure
- rewind all the student cassette recorders
- insert a test cassette (cassette containing some quality speech or music) into a master recorder and check the quality of sound by playing the tape. If the sound quality is poor clean the master recorder heads (see head cleaning) and try again. If the sound quality is still poor check the ‘head azimuth’ (see Head Alignment).
NOTE: It is important that the master recorder sound quality is of the highest level possible because the quality of the student tape copies will only be as good as (or less than) the quality of the sound from the master player.
- transfer 10minutes of sound from the master (test) tape to the student recorders (see the operation manual for the particular type of laboratory you are using)
- when the transfer is completed rewind the student tapes and start them playing
- monitor the playback quality of each student recorder briefly using the individual monitor buttons on the teacher console
NOTE: Check for level and clarity (quality) of the sound from the student recorders. Using this method it is easy to identify the general condition of the heads of the recorders in the entire laboratory. If more than two recorders need their heads cleaned – clean the heads in all the recorders including the master recorders (see head cleaning) and make a record of the date in your maintenance log (this information will help schedule future head cleaning).
- go to each student unit and put on the headphones. Test the operation of the main student unit controls (FF/REW/PLAY)
- press the tape play button and listen carefully to the quality of the sound in both ear-pieces. Gently rub your fingernail against the microphone. You should be able to hear the scratching sound clearly in both ear-pieces (check that the student volume is turned up)
- with the headphones still on, gently wriggle the cables, especially close to the plug and each ear-piece. If there is any crackling, or if the sound disappears you can usually repair the fault by cutting the cable near the break and re-terminating the cable (see soldering).
- rewind all student recorders so that they are ready for use by the next teacher
3. STUDENT AND MASTER RECORDERS
Head Cleaning (Weekly)
AAC Laboratories – All master and student units
AA Laboratories – Master units only

The audio heads on a cassette recorder have a vertical gap across which a changing magnetic field imprints a magnetic sound track upon the cassette tape. It is most important that this gap is kept clean and free from a build-up of the magnetic oxide from the cassette tape and also dust from the environment. If this gap becomes ‘dirty’ the general quality of the sound deteriorates and may be of a low level and not very clear.
There are two main heads on cassette recorders, the record/ playback head, and the erase head. However, when we are cleaning the heads all of the parts of the cassette recorder that come into contact with the tape also need to be cleaned. These include the capstan, pinch roller, and any tape guides (see diagram *).
Using a cotton bud and alcohol or head cleaning fluid (Head cleaning kits are also available):
- turn on the master console
- open the door to the cassette compartment
- moisten the cotton bud with alcohol or head cleaning fluid (not too wet) and wipe the surfaces of the heads thoroughly, finishing with vertical up and down movements to make sure the head gap is clean.
- to clean the capstan press the play, then the pause button to get the capstan rotating. Clean the rotating capstan by holding a moistened cotton bud against it. If the cotton on the cotton bud twists around the capstan turn off the cassette player and the cotton should slide up off the capstan.
- to clean the pinch roller release the pause button and the roller will rotate. Hold the moistened cotton bud against the roller, moving it up and down to remove all the oxide and dust.
NOTE:
- It is especially important to clean the pinch roller and capstan thoroughly because a build-up of oxide or dust on them can make them "sticky". If they become sticky the tape can adhere to them and can cause a major tape-jam seriously damaging the tape.
- After cleaning the pinch roller also inspect its surface and make sure that it is flat and even (no signs of permanent wear or deterioration). If there are signs of significant wear order (or acquire locally) suitable replacements immediately and schedule a replacement date. Delays may result in serious tape damage or erratic performance.
- clean all other surfaces that come into contact with the tape ie. tape guides
- allow sufficient time for the cleaned surfaces to dry before using the equipment.
Head Demagnetization

The cassette recorder covers have only been removed from the cassette recorder to assist visibility for the photographs.
In the photo the demagnetizer is demagnetizing the erase head (top right).
Head demagnetizing is usually recommended to improve sound quality and the frequency response capability of the audio heads which may have become partially magnetized. However, probably the main reason for periodic head and tape-path demagnetization is more of a preventative procedure to avoid the possibility of partial erasure of the master or student tapes. Partial erasure can occur when pre-recorded tapes pass by magnetized objects. Demagnetizing removes the residual magnetism that can build up on the tape heads, guideposts and other parts in the tape path. Small hand held head demagnetizers are available from some local audio and electronics shops (alternatively - from Glodok in Jakarta).
Procedure
- switch off the cassette recorder and pull the plug out of the power socket
- plug the head demagnetizer into the power but do not switch it on until you are ready to use it
- check that the soft plastic (anti-scratch) cover is in place on the head-demagnetizer tool
- open the cassette compartment door (on some cassette recorders the door is removable and this can make access easier)
- hold the demagnetizer at a distance of about 600mm from the recorder and turn it on. Slowly move it towards the recorder and place the tip against (in contact with) the heads, capstan, and guides - rotating it slowly against their metal surfaces.
- when you have finished slowly take the demagnetizer back a distance of at least 600mm from the recorder before switching it off (otherwise there is a possibility of leaving some residual magnetism on the heads when the demagnetizer is turned off).
Head Alignment
AAC Laboratories – All master and student units
AA Laboratories – Master units only

As mentioned in the Head Cleaning section, the audio heads have a vertical gap in their magnetic circuit. For quality reproduction it is also very important that this gap is at right-angles to the direction of the tape movement. If the head is not correctly aligned the first thing that you will notice is that the high frequency sounds are low in level or can not be heard at all. The audio will not be crisp and clear.
This alignment is called "Azimuth Alignment" and is another basic performance check which should be conducted at regular intervals - at least twice each year. The alignment should only require about one minute per tape machine. For a 24 position AAC language laboratory (including the master recorders) it shouldn’t take any longer than approximately 30 minutes.
To align the azimuth of the tape machines you will require a "test tape". Special test tapes are available commercially, however, they are expensive. You can do a reasonable azimuth alignment using a quality commercially produced music tape by adjusting the azimuth to achieve the clearest high frequency reproduction. You can also make a simple (but adequate) test tape using a new cassette recorder and an audio signal generator. A suitable audio signal generator should be available from the science (IPA) laboratory in your school (see: Making a simple azimuth test tape).
Azimuth Alignment (Procedure)

Again, the cassette recorder's case has been removed only to improve visibility of the heads for the photographs. When you do this adjustment the recorder will actually contain a cassette and be in the play mode.
1.One side of the Record/ Playback Head is supported by a spring and screw arrangement (see the diagram). This screw allows adjustment of the head’s azimuth.
2. De-magnetize the Record/ Playback heads (see Head Demagnetization)
3. Insert the cassette tape that you are going to use into the recorder.
4. Start the tape playing (press PLAY).
5. Listen carefully to the sound being reproduced from the tape. Using a non-magnetic (de-magnetized) screwdriver (special alignment tools are available with plastic shafts) very slowly rotate the azimuth adjustment screw to the left and to the right selecting the position where the high frequencies are clearest and strongest.
Note:
Some cassette players have a special access hole above the azimuth adjustment screw (when the tape heads are in the play position) for this purpose. On the Tandberg System 500 recorders a small panel above the heads can be removed completely.
Making a Simple Azimuth Test Tape
- Choose the most recently purchased cassette recorder available.
- Demagnetize the tape heads and tape path components (see Head Demagnetization).
- Insert a new (empty) cassette tape into the tape machine and fast forward it to the end and then rewind it to the beginning again.
- Connect an audio signal generator output to the input of the cassette recorder (Line Input, or Microphone Input socket).
- Set the cassette recorder in RECORD mode and press PAUSE.
- Turn the audio signal generator on and record (release the PAUSE button) 2 minutes of signal at 8,000 Hz. Check the quality of the recording by playing the tape. If the sound is distorted reduce the level of the sound (attenuate) from the signal generator and try again.
- Record 2 minutes of sound at 8,000 Hz, another 2 minutes at 10,000 Hz, and another 2 minutes at 12,000 Hz.
- On the other side of the tape record 30 minutes of signal at 12,000 Hz. This is the side that you will normally use for doing the Azimuth test.