Service I Adjustment Remarks; Service Tools - Philips 70DCC600 Service Manual

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