Panasonic TX-28PB50F, Service Manual

CONTENTS

SAFETY PRECAUTIONS..........................................................................................................................................................2

SERVICE HINTS .......................................................................................................................................................................3

ADJUSTMENT PROCEDURE AND FACTORY SETTINGS .....................................................................................................4

WAVEFORM PATTERN TABLE ...............................................................................................................................................5

ALIGNMENT SETTINGS...........................................................................................................................................................6

BLOCK DIAGRAMS ..................................................................................................................................................................7

PARTS LOCATION .................................................................................................................................................................12

REPLACEMENT PARTS LIST ................................................................................................................................................13

SCHEMATIC DIAGRAMS .......................................................................................................................................................44

CONDUCTOR VIEWS.............................................................................................................................................................55

SAFETY PRECAUTIONS

GENERAL GUIDE LINES

1.  It is advisable to insert an isolation transformer in the

a.c. supply before servicing a hot chassis.

2.  When servicing, observe the original lead dress in the

high voltage circuits. If a short circuit is found, replace
all parts that have been overheated or damaged by
the short circuit.

3.  After servicing, see that all the protective devices

such as insulation barriers, insulation papers, shields
and isolation R-C combinations are correctly
installed.

4.  When the receiver is not being used for a long period

of time, unplug the power cord from the a.c. outlet.

5.  Potentials as high as 33kV are present when this

receiver is in operation. Operation of the receiver
without the rear cover involves the danger of a shock
hazard from the receiver power supply. Servicing
should not be attempted by anyone who is not
familiar with the precautions necessary when working
on high voltage equipment. Always discharge the
anode of the tube.

6.  After servicing make the following leakage current

checks to prevent the customer from being exposed
to shock hazard.

LEAKAGE CURRENT COLD CHECK

1.  Unplug the a.c. cord and connect a jumper between

the two prongs of the plug.

2.  Turn on the receiver’s power switch.
3.  Measure the resistance value with an ohmmeter,

between the jumpered a.c. plug and each exposed
metallic cabinet part on the receiver, such as screw
heads, aerials, connectors, control shafts etc. When
the exposed metallic part has a return path to the
chassis, the reading should be between 4M ohm and
20M ohm. When the exposed metal does not have a
return path to the chassis, the reading must be
infinite.

LEAKAGE CURRENT HOT CHECK

1.  Plug the a.c. cord directly into the a.c. outlet. Do not

use an isolation transformer for this check.

2. Connect 

a 

2k

Ω

 10W resistor in series with an

exposed metallic part on the receiver and an earth,
such as a water pipe.

3.  Use an a.c. voltmeter with high impedance to

measure the potential across the resistor.

4.  Check each exposed metallic part and check the

voltage at each point.

5.  Reverse the a.c. plug at the outlet and repeat each of

the above measurements.

6.  The potential at any point should not exceed

1.4V rms. In case a measurement is outside the limits
specified, there is a possibility of a shock hazard, and
the receiver should be repaired and rechecked before
it is returned to the customer.

X-RADIATION WARNING

1.  The potential sources of X-Radiation in TV sets are

the high voltage section and the picture tube.

2.  When using a picture tube test jig for service, ensure

that the jig is capable of handling 33kV without
causing X-Radiation.

NOTE: It is important to use an accurate periodically
calibrated high voltage meter.

1.  Set the brightness to minimum.
2.  Measure the high voltage. The meter should indicate.

30.5kV ± 1kV (28”) , 32kV ±  1kV (32”/36”).
If the meter indication is out of tolerance, immediate
service and correction is required to prevent the
possibility of premature component failure.

3.  To prevent any X-Radiation possibility, it is essential

to use the specified tube.

HOT CHECK CIRCUIT

a.c. VOLTMETER

WATER PIPE

(EARTH)

TO INSTRUMENT’S EXPOSED
METALLIC PARTS

Fig. 1.

2k

Ω

 10 Watts

2