Sony TC-PB5 - Repair Precautions: Shut-Off and IC Handling; Shut-Off Detection Mechanism; MOS IC Handling Guidelines

Shut-Off Detection and Precaution On Repairing
In this set, the shut-off detection is made optically.
The take-up reel spindle has the five holes. The light
of the lamp received by the light guide is inter-
mettently applied to the photo transistor by means of
the rotation of the reel spindle. The pulse generated
by the photo transistor Q803 is amplified by Q801
and is fed to the mechanism control IC302.
Accordingly, when it is necessary to repair the unit
after removing the ornamental plate, connect an af
oscillator to the terminal Q) of IC303 as shown
below, so as not to operate the shut-off mechanism.
light guide “ote
%
photo transistor Ny
~~!
“N
\
“XN
10Hz — nes)
10dB
oe,
ni 0.01uF
OSC
ornamental plate
take-up reel spindle
hole
MAIN BOARD (Conductor side)
Handling Precautions for MOS ICs
Generally, the insulation resistance of the oxide
layer in MOS IC structures is very high, and the oxide
layer is very thin. Because of this, it is possible that
the static voltages usually present on clothes and the
human body will be enough to generate a potential
difference across the insulator, high enough to cause
a breakdown of the insulating layer.
The following precautions should be taken while
handling these ICs.
(Particular care should be taken under conditions
of low humidity.)
Precautions in Replacing MOS ICs
1. Store newICs by inserting them into a urethane-
polyester cushion (which is somewhat conduc-
tive), or wrapping it in aluminum foil, so that
all the pins are at the same potential.
(The ICs should be stored in that manner until
mounted on the circuit board.)
Fig. A partially conductive
unrethane-polyester
cushion
IC
Fig. B aluminum foil
2. Check the soldering iron for possible power-line
leakage current. Make sure that there is no
leakage path by connecting an ohmmeter to the
tip of the soldering iron and the plug as shown
in Fig. C. If there is a leakage path, use some
other soldering iron.
VOM
(2.x 10,000 range)
3. Equalize any potential difference between the
clothes, the tools in use, the work bench, the
set being worked on, and the packaged IC by
touching them all in succession with the hands
or a conductive wire or tool.
4. The following are effective methods for handl-
ing ICs that remove the potential difference
across the oxide layer.
@ Use a paper clip modified by soldering ina
wire braid insert.
wire braid
clip
>)
ye
le
S soldered
soldered
sli
, Make sure that there is
Fig. D no solder on the inside.
clip
partially conductive
. urethane-polyester
Fig. E cushion or aluminum
oll
wire braid
clip
(ooo res
WY
Make sure that all the pins are in
contact with the wire braid (all
. the pins will then be at the same
Fig. F __ potential.).