SERVICE REMARKS
DCC-head
The heads used
in
the DCC-system are called "thin film head" and made by repeating
20
times or more of multiple evaporations
and spatterings
as
in
fabricating ICs.
Accordingly, the heads have different features
and
characteristics from those of coil winding type heads used
in
conventional
analog cassette tape decks:
- The playback head uses a magnetic resistive element (MRH)
- The
MRH
needs magnetic bias
to
obtain
its
maximum output. So, a bias conductor which is equivalent
to
a coil
to
develop the
magnetic bias is installed.
- Moreover, the analog playback head needs a magnetic feedback
to
increase linearity. This is realized by giving a magnetic
field proportional
to
the MR-element output from a bias conductor.
For terminals
and
structure of the DCC-head see page
50,
circuit diagram read/write board.
Handling DCC-heads
Caution: The heads are susceptible
to
electrostatic voltage higher than 150Voc. The heads are protected from external
electrostatic charging by connecting the head flexible cables
to
the read/write board. When disconnecting the cables, always
place the deck
on
a bench with required electrostatic discharging measures taken and wear
an
electrostatic discharging band.
Moreover, always mount the short-clip
on
the flexible cables removed.
The heads are also susceptible
to
strong external magnetic field and the analog output may be affected.
Do
not use a head
demagnetizer, etc.
WARNING
DO NOT USE A DEMAGNETIZER
CASSETTE!
Adjustment remark - recording current
For each head, a recommended recording current exists individually (120
..
180mA).
If
this value
is
not adjusted correctly, the
RDMUX value does not match between a self recorded tape and prerecorded tape. Moreover, if a recording
is
made at a deep
layer with a high value, the previous records can not be erased when
an
overwrite recording is made at that area later.
As
a
consequence the error rate will be increased at that area.
The
adjustment
of
the
recording
current
requires an accuracy
of
±O,2dB - a very
close
tolerance
which
can
not
be
realized
without
special
adjustment
jigs.
Therefore: When the DCC-head
or
the
write-amplifier has
to
be replaced exchange the
whole
loading-assy
(4822691 20833). The
loading
assy, delivered,
is
adjusted
by
the factory. Only
adjustments
which
have
to
be carried
out
on
the
main-board have
to
be
done
in
the
repair
shop
(tape speed, take-up torque,
dolby
level).
SERVICE TOOLS
TORX
screwdriver
set "SBC163"
Universal analog test cassette
Cr02
"SBC419"
Universal analog test cassette Fe "SBC420"
9,6kHz calibration cassette (prerecorded DCC)
Audio
performance
test
cassette (prerecorded DCC)
General
purpose
test
cassette (prerecorded DCC)
Torque measurement cassette
"811
CTM"
Tape
guide
gauge "ABEX THG-801"
Head
mounting
support
(see page 58)
29
482239550145
4822 397 30069
482239730071
4822 397 30264
4822 397 30255
4822 397 30256
4822 395 30054
482231050108
4822 403 70846
CS
45
927
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