Sony KD-55A8F Service Manual page 8

4) Look for unauthorized replacement parts, particularly transistors that
were installed during a previous repair. Point them out to the customer and
recommend their replacement.
5) Look for parts which, though functioning show obvious signs of
deterioration. Point them out to the customer and recommend their
replacement.
6) Check the line cords for cracks and abrasion. Recommend the
replacement of any such line cord to the customer.
7) Check the antenna terminals, metal trim, metalized knobs, screws and all
other exposed metal parts for AC leakage. Check leakage test as described
next.
8. For safety reasons, repairing the Power board and/or Inverter board is
prohibited.
1-5.Leakage Test
(To protect electric shock when customer touch the terminal.)
Leakage current can be measured by V: Voltmeter or oscilloscope (r.m.s. or
peak reading)
Stabilized power supply instrument and isolated voltage transformer:
Use too much current capacity and isolated voltage transformer does not
need to use stabilized power supply equipment.
Specification of RMS volt meter: Input resistance > 1 Mohm, Input
capacitance < 200 pF, Frequency range: 15 Hz – 1MHz . Refer Figure 2.
Isolated type volt -meter (FLUKE 8921A etc *1)
*1 Not use FLUKE 8920A that connected to protective earth by diode
# Leakage current of measurement instrument is less than 10μArms when
under test equipment AC plug is opened
# Set up the following condition and turn on the set. Applied voltage:
Nominal input voltage (Description on Nameplate)
# Measure the leakage current between one phase conductor and neutral
for terminal A and terminal B.
Read rms value, and then calculate to peak value PEAK VALUE =√2 RMS
VALUE
Comply with the following requirement
Class II equipment (2-pin plug): for each terminal, the worst value of
measurement must not exceed AC 350uA peak).
Note: including AC adaptor, AC adaptor/DC operated unit combination
1-6. How to Find a Good Earth Ground
1) A cold-water pipe is a guaranteed earth ground; the cover-plate
retaining screw on most AC outlet boxes is also at earth ground.
2) If the retaining screw is to be used as your earth ground, verify that it is
at ground by measuring the resistance between it and a cold-water pipe
with an ohmmeter. The reading should be zero ohms.
3) If a cold-water pipe is not accessible, connect a 60- to 100-watt trouble-
light (not a neon lamp) between the hot side of the receptacle and the
retaining screw. Try both slots, if necessary, to locate the hot side on the
line; the lamp should light at normal brilliance if the screw is at ground
potential (see Figure 3).
Figure 2 – Measuring network
for Leakage Current
Figure 3. Checking for earth
ground.
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SYS SET