Table of Contents
Advertisement
6.3 Erase Head
6.3.1 Height Adjustment
2-track:
The height is adjusted with screws 6 and 7. Approxi-
mately 0.1 mm (4 mil) of the head gap should be
visible above the upper edge of the tape. Headfront
and tape must be parallel. Fig. 6.2 shows the correct
position of the tape with respect to the head.
4-track:
As for 2-track model, except that approximately 0.2
mm (8 mil) of the erase head gap should be visible
above the tape.
6.3.2 Azimuth Adjustment
Adjust screw 8 to bring the head baseplate into
parallel alignment with upper mounting plate.
6.3.3 Lateral Adjustment
Check that the tape touches the head in the middle
of the curved surface. In other words angles c and d
should be equal.
6.4 Track Control
6.4.1 Visual Control with Test Tape, 2-Track Model
Check that the tape runs as shown in figs. 6.2 and 6.3.
6.4.2 Track Control with Test Tape, 4-Track Model
Play back a Tandberg Test Tape no. 1 (1000 Hz full
track at constant level, with a 30 dB reduction of
track 3). Set OUTPUT VOLUME to maximum and
the track selector to EXTRA (playback track 3). Ad-
just the height of the record/playback head with
screws 1 and 2 until minimum voltage is measured
at the PREAMP output.
Check the azimuth position according to paragraph
6.2.3.
6.4.3 Height Adjustment of Record/Playback Head by
Track Measurement on 4-Track Model
On a new or erased tape record a 1 000 Hz signal
well above normal level, first with the track selector
in position NORMAL (track 1), then in position EXTRA
(track 3). Turn the tape around and record in the
opposite direction for both positions of the track
selector (track 4 and 2). Cut off a piece of the tape
and dip it in Magna-See solution or sprinkle iron
oxide powder on the tape. The recorded tracks will
then appear as four dark stripes approx 1 mm (40
mil) wide, with narrower spacings in a lighter shade.
The spacings should have equal width, and the two
outer dark stripes should flush with the tape edge.
If the tracks are not correctly distributed across the
width of the tape, the height of the record/playback
head should be readjusted with screws 1 and 2. Use
both screws to maintain the headfront in parallel
alignment with the capstan. Recheck azimuth posi-
tion. The use of special tools is recommeded.
6.5 Bias Current
6.5.1 Oscillator Frequency, 2-Track Model
Connect a 100 ohm resistor in series with the record/
playback head and ground. Set the function selector
to RECORD and the operating lever to normal for-
ward drive. Connect a frequency meter across the
resistor and adjust C221 for a frequency reading of
85.5 kHz.
Bias Current
Adjust C2 for a voltage reading of 85 mV across the
100 ohm resistor (corresponds to 850 uA bias cur-
rent).
6.5.2 Oscillator Frequency, 4-Track Model
Set the track selector to NORMAL. Set the function
selector to RECORD, and the operating lever to nor-
mal forward drive. Measure the frequency across a
100 ohm resistor connected in series between upper
half of the record/playback head and ground. Adjust
C221 for a frequency reading of 85.5 kHz. Then set
the track selector to EXTRA and connect the fre-
quency meter across a 100 ohm resistor in the lower
half of the record/playback head. The frequency
reading should be 85.5 kHz ± 2.5 kHz. If the fre-
quency falls outside one of these limits, adjust C221
to obtain an equal departure from the nominal fre-
quency in both positions of the track selector.
Bias Current
Measure the voltage across the 100 ohm resistor with
the track selector in position NORMAL and EXTRA.
Adjust to 65 mV with C2 and C1 respectively (cor-
responds to 650 vA bias current).
6.6 Record Current and Record Level
Indicator
Connect a voltmeter across a 100 ohm resistor in-
serted in series between the record/playback head
and ground. In 4-track models, the track selector
should be set to NORMAL and a 100 ohm resistor
connected in series with upper half of the record/
playback head. Short-circuit terminals 26 and 27 on
board 15001 (or short circuit erase head).
Feed a 400 Hz signal into the pick-up input and set
the recorder for recording. Adjust LINE for the fol-
lowing voltmeter readings:
2-track:
18 mV (180 ,LA)
4-track:
12 mV (120 vA).
Finally set R225 for 0 dB reading on the record level
indicator.
6.7 Verification of Frequency Curves
The overall frequency curves should lie within the
tolerance ranges specified in DIN 45511. (Fig. 6.4).
See paragraph 8.1 for recorders with serial no. above
2 619 561 for series 14 and 2 515 502 for series 15
which are adjusted for Low Noise tape.
28
Hide quick links:
Advertisement
Table of Contents
