HITACHI 50FX48B
Service Manual

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

REVERSED (USING AC ADAPTER PLUS AS REQUIRED)

this instrument or permit it to be operated without

aH 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.

AC Leakage Test ANY MEASUREMENTS NOT WlTHlN THE LlMlTS SPEClFlED HERElN lNDlCATE A POTENTlAL SHOCK HAZARD THAT MUST BE ELlMlNATED BEFORE RETURNlNG THE lNSTRUMENT TO THE CUSTOMER OR BEFORE CONNECTlNG THE ANTENNA OR ACCESSORIES. e. 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.

c. 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.

f. Service Warning -With maximum contrast, operating high voltage in this receiver is lower than 31.6 kV. In case any component having influence on high voltage is replaced, confirm that the high voltage with maximum contrast is lower than 31.6 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.

d. 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) Cl 01 .O 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.

Chassis ground

I

I
Deflection P.W.B.

High Impedance H.V. meter

FBT (T702)

\ High voltage connector