Hitachi 51SWX20B Service Manual Download

Page: 3 / 189

DP27/27D

IMPORTANT SAFETY INSTRUCTION

1. Before returning an instrument to the customer, always

make a safety check of the entire instrument, including
but not limited to the following items.
a. Be sure that no built-in protective devices are

defective and/or have been deleted during servicing.
(1) Protective shields are provided on this chassis to
protect both the technician and the customer.
Correctly replace all missing protective shields,
including any removed for servicing convenience. (2)
When reinstalling the chassis and/or other assembly
in the cabinet, be sure to put back in place all
protective devices, including but not limited to,
nonmetallic control knobs, insulating fishpaper,
adjustment and compartment covers/shields, and
isolation resistor/capacitor networks.

Do not operate

this instrument or permit it to be operated without
all protective devices correctly installed and
functioning. Servicers who defeat safety features
or fail to perform safety checks may be liable for
any resulting damage.

b. Be sure that there are no cabinet openings through

which an adult or child might be able to insert their
fingers and contact a hazardous voltage. Such
openings include, but are not limited to (1) spacing
between the picture tube and cabinet mask, (2)
excessively wide cabinet ventilation slots, and (3) an
improperly fitted and/or incorrectly secured cabinet
back cover.

Antenna Cold Check

– With the instrument AC plug

removed from any AC source, connect an electrical
jumper across the two AC plug prongs. Place the
instrument AC switch in the on position. Connect one
lead of an ohmmeter to the AC plug prongs tied
together and touch the other ohmmeter lead in turn to
each tuner antenna input, exposed terminal screw
and, if applicable, to the coaxial connector. If the
measured resistance is less than 1.0 megohms or
greater than 5.2 megohms, an abnormality exists that
must be corrected before the instrument is returned to
the customer. Repeat this test with the instrument AC
switch in the off position.

Leakage Current Hot Check

– With the instrument

completely reassembled, plug the AC line cord
directly into a 120V AC outlet. (Do not use an isolation
transformer during this test.) Use a leakage current
tester or a metering system that complies with
American National Standards Institute (ANSI) C101.0
Leakage Current for Appliances and Underwriters
Laboratories (UL) 1410, (50.7). With the instrument
AC switch first in the on position and then in the off
position, measure from a known earth ground (metal
waterpipe, conduit, etc.) to all exposed metal parts of
the instrument (antennas, handle bracket, metal
cabinet, screw heads, metallic overlays, control
shafts, etc.), especially any exposed metal parts that
offer an electrical return path to the chassis. Any
current measured must not exceed 0.5 milliamps.
Reverse the instrument power cord plug in the outlet
and repeat test.

ANY MEASUREMENTS NOT WITHIN THE LIMITS
SPECIFIED HEREIN INDICATE A POTENTIAL
SHOCK HAZARD THAT MUST BE ELIMINATED
BEFORE RETURNING THE INSTRUMENT TO THE
CUSTOMER OR BEFORE CONNECTING THE
ANTENNA OR ACCESSORIES.

High Voltage –

This receiver is provided with a hold

down circuit for clearly indicating that voltage has
increased in excess of a predetermined value.
Comply will all notes described in this Service Manual
regarding this hold down circuit when servicing, so
that this hold down circuit may correctly be operated.

Service Warning –

With maximum contrast, operating

high voltage in this receiver is lower than

30.5 kV.

case any component having influence on high voltage
is replaced, confirm that the high voltage with
maximum contrast is lower than

30.5 kV.

To measure H.V. use a high impedance H.V. meter.
Connect (-) to chassis earth and (+) to the CRT anode
button. (See the following connection diagram.)

Note:

Turn power switch off without fail before the

connection to the anode button is made.

LEAKAGE
CURRENT
TESTER

(READING
SHOULD NOT
BE ABOVE 0.5mA)

EARTH
GROUND

TEST ALL
EXPOSED
METAL SURFACES

DEVICE
UNDER
TEST

2-WIRE CORD

ALSO TEST WITH PLUG
REVERSED
(USING AC ADAPTER
PLUS AS REQUIRED)

Chassis
ground

High Impedance
H.V. meter