Ci Rc Uit S; Oscillator; Photo End-Stop - TANDBERG 3400 X Service Manual

CI R CUI T S
8.2
PHOTO END-STOP
8 .1
O S C IL L A T O R
fhe os ci llator freq u enc y i s g5 .b k lf z for
a st er eo
recording. N.{easure this frequency rvith
a frequenc_v
counter on the bias head and acljust r,vith
C502 on
t he os cill ator boar d .
8.
;\
0
I
r
a
8.1. 1
Er ase v olta g e
Prepare the machine for a stereo recording.
Connect a VVN{ to the upper half of the erase
head
via a lowcapacity^p^robe.-Check that the
voltage is
betw een 80 and 120 V. Che c k rha t t he ,u * .
r. i l t og .
appears across the bottom half of the head.
Set thl
machine to record on channel L, ancl check
that
the voltage is the same on the upper half
of the
head. The permissable difference^between
the
voltages on the two halves of the head from
a
stereo recording is l0 V max. Carry out
the same
check for channel R.
8. 1. 2
B ias c urren t, p re -ad ju s tme nt
Prepare the machine for a stereo recording,
ancl
use a VVX{ to measure the voltage across ih.
r.,pp.,
half of the bias head. Adjust the"voltas e to
22 y
by m eans of R 401. C he & r ha t th e uol i ag e
acro ss
the bott om half of t he he ad is 22 V a nd i d j ust
by m eans of R 400.
Demagnetize the heads and tape path.
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Fig. 8.1. Osctllator boartl.
]3,c hanS e
th e lamp, ta k e th e sc r erv o ut of th e ta pe
gulde post, pr-rsh the photo end_stop unit
back, and
lift it up. Se e Figure g .2 .
Th.e sensitivity of the photo end_stop can
be
ad justed by m eans o f nS lZ on t he os c il l a tor
bo ard .
S ee Figur e 8 .1.
G,
Fig. 8.2. Photo ent! stop.