Bias Head; Era Se He A D - TANDBERG 3400 X Service Manual

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5.4
BIAS HEAD
Vertical adjustment
Move the operating lever slowly to the normal for-
ward drive position ( I ) and check that the head-
front of bias and record heads are parallel. If
necessary, bend the arm of the bias head as required.
Height adjustment
Se t th e dec k t o the stereo
screw the locking screw H
turn.
re co rd mo de, a nd u n-
(F ig ure 1 0.1 ) a bo ut o n e
,({\
1
Connect an a.c. voltmeter across each half of the
record head. Nlove the bias head up or down by
me an s of adjust m ent sc rew M (F ig ur e 1 0. 1) f or
the highest possible reading on the voltmeter.
Check that the tape runs freely in the groove in
front of the bias head, and that there is sufficient
clearance between the bias head and the mounting
plate for the record head. If necessary, raise the
bias head slightly. The height position of the bias
head is not critical. Before tightening screw H,
carry out the horizontal adjustment as follows.
Horizontal adjustment
C o nn e ct an a. c. volt meter ac ro ss e ac h h al f of the
record head and set the deck to the stereo record
mode. Insert a screwdriver in the groove shown in
Figure 5.2 and tilt the bias head to the right. Then
tilt the bias head carefully by means of the screw-
driver towards the left until the induced voltage
(bias) in the record head increases to a maximum.
Continue tilting the head towards the left until
the induced voltage (bias) in the record head is
re dr.r c ed to betw een 10 and lS Yob el ow ma x imu m.
Tighten screw H while maintaining the correct
horizontal position for the head. Then re-check the
output voltage. If the voltage has changed notice-
able, the horizontal adjustment procedure must
be re peated.
Fig. 5.2. Ilorizontal adjustment for the bias head.
5. 5
E RA S E H EA D
Height adjustment
By visual inspection, check that approximately
0 .2 5 m m ( 0 . 0 1 ") o f t h e u pp e r h a l f o f t h e e r a s e
head is visible above the tape, see Figure 5.3. Insert
'fandberg test tape No. 9 and record on channel R
a 400 Hz signal well above normal recording level.
Dip the tape in a solution of fine-grained iron-oxide
powder and alcohol (Ntlagna See). Check that the
recorded track is positioned in the centre of the
e ra se d t r a c k , s e e F i g u r e 10 . 3 , p a g e 2 1.
Ap pr ox. 0 .2 5 mm o f
up pe r f er rit e core visib le
above tape.
{(\
l- s )-==-
\i._,-===-
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Vrl
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Fig. 5.3. Four trech erase head.