c. If the bias oscillator is not working and the-machine uses this same signal to erase the tape, a
recorded tape would not be erased prior to a new recording. This is one quick check of the bias
d. A substitute microphone can be used to make a quick check of the input source. Many
recorders have a monitor jack which can be used to determine whether a signal is being fed into the
recorder. Most recorders have a record indicator, either a light or a meter, which gives a visual
indication of the input. By checking the circuit of the recorder in use, you can, through a process of
elimination, narrow the area of trouble to a limited number of stages.
e. From this point, it is necessary to make the more routine checks of tubes and other
components. To prevent head magnetization, do not check the continuity of heads with an ohmmeter.
f. The following check list is suggested for locating the cause of poor high-frequency response
due to head problems.
(1) Check azimuth alignment with an alignment tape.
(2) Check for tape skewing which seems to occur simultaneously with amplitude
(3) Check to be sure the head meets the tape squarely.
(4) Check for stability of the tape path in its guides.
(5) Check for foreign deposits, nicks, or gauges on the head surface.
(6) Check for "breakthrough" in the head gap. A magnifying glass or microscope is helpful.
(7) Check for uneven wear.
(8) Replace the head if necessary.
Playback problems. A trouble in the playback circuits is most readily found by using a known
good tape for playback. With some machines you have an intermediate output which can be checked to
determine whether or not the signal is reaching a given point in the machine.
a. Some machines have a visual output indicator; if you have this type, you know that all
circuits are good up to a stage prior to the power output; here, all but the last stage could be eliminated
as the source of trouble.
b. In all cases, it is a matter of taking logical steps toward localizing the trouble to an area, to a
circuit, and finally, to a component or components.