Panasonic TX 28MD4 Service Manual

TX-28/25/21MD4 Service Manual

Safety

Specifications

Parts List

Service

Information

Adjustments

Self Check

Service Hints

Mechanical

View

Disassembly

Location of

Controls

Waveforms

Supplementary Information

Block Diagrams

Schematic Diagrams

PCB Views

Service Support

Service and repair of
this product is
supported by
Panasonic's LUCI
interface.

This interface provides a
link between the TV and
a standard PC to allow a
number of diagnostic
and control functions to
be performed.

For more details contact
your local Panasonic
company.

BACK

EXIT

Audio

Control

Power supply

Video

BACK

E - PCB Y - PCBs

BACK

E - Schematics H - Schematic

Y - Schematics

BACK

SPECIFICATIONS

(Information in brackets { } refers to model TX-25MD4)
(Information in brackets [ ] refers to model TX-21MD4)

Power Source: 220-240V AC, 50Hz
Power Consumption: 85W [71W]
Aerial Impedance: 75Ω unbalanced, Coaxial Type
Stand-by Power

Consumption: 1,8W
Receiving System: PAL I, PAL 525/60

M.NTSC
NTSC (AV only)

Receiving Channels: UHF E21 - E69

Intermediate Frequency:

Video 39,5MHz
Audio 33,5MHz, 32,95MHz
Colour 35,07MHz (PAL)

Video/Audio
Terminals:

AUDIO MONITOR OUT Audio (RCAx2) 500mV rms 1kΩ
AV1 IN Video (21 pin) 1V p-p 75Ω

Audio (21 pin) 500mV rms 10kΩ
RGB (21 pin)

AV1 OUT Video (21 pin) 1V p-p 75Ω

Audio (21 pin) 500mV rms 1kΩ

ORDER No. SM-98017

Colour Television

TX-28MD4
TX-25MD4
TX-21MD4

EURO4 Chassis

AV2 IN Video (21 pin) 1V p-p 75Ω

Audio (21 pin) 500mV rms 10kΩ
S-Video IN Y: 1V p-p 75Ω
(21-pin) C:0.3V p-p 75Ω

AV2 OUT Video (21 pin) 1Vp-p 75Ω

Audio (21 pin) 500mV rms 1kΩ
Selectable output (21 pin)

AV3 IN Audio (RCAx2) 500mV rms 10kΩ

Video (RCAx1) 1V p-p 75Ω

High Voltage: 28,5kV ±1kV {28,2kV ±1kV}

[28kV ±1kV]

Picture Tube: A66ECF50X41 66cm

{A59ECF50X41 59cm}
[A51ECQ51X01 51cm]

Audio Output: 2 x 15W (Music Power)

8Ω Impedance

Headphones: 8Ω Impedance

3,5 mm

Accessories
supplied : Remote Control

2 x R6 (UM3) Batteries
TV Stand

Dimensions:

Height: 580 mm {531 mm} [478 mm]
Width: 666 mm {601 mm} [525 mm]
Depth: 472 mm {439 mm} [480 mm]

Net weight: 31kg {25kg} [22kg]
Specifications are subject to change without notice.

Weights and dimensions shown are approximate.

3DQDVRQLF

NOTE: This Service Manual should be used in conjunction with
the EURO4 Technical guide.

Panasonic CS ( U.K. ) Ltd.

WILLOUGHBY ROAD,

BRACKNELL,

BERKS.,

RG12 8FT.

CONTENTS

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

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

SERVICE POSITION.................................................................................................................................................................4

ADJUSTMENT PROCEDURE...................................................................................................................................................5

ADJUSTMENT PROCEDURE AND SELF-CHECK ..................................................................................................................6

WAVEFORM PATTERN TABLE...............................................................................................................................................7

ALIGNMENT SETTINGS...........................................................................................................................................................8

BLOCK DIAGRAMS.................................................................................................................................................................. 9

PARTS LOCATION.................................................................................................................................................................13

REPLACEMENT PARTS LIST................................................................................................................................................ 14

SCHEMATIC DIAGRAMS.......................................................................................................................................................23

CONDUCTOR VIEWS.............................................................................................................................................................28

SAFETY PRECAUTIONS

GENERAL GUIDE LINES

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

5. Potentials as high as 29,5kV {29,2kV} [29kV] 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 AC 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 AC 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 AC cord directly into the AC outlet. Do not
use an isolation transformer for this check.

2. Connect a 2kΩ 10W resistor in series with an
exposed metallic part on the receiver and an earth,
such as a water pipe.

3. Use an AC 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 AC plug at the outlet and repeat each of
the above measurements.

6. The potential at any point should not exceed

1.4 Vrms. 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.

HOT CHECK CIRCUIT

A.C. VOLTMETER

2kΩ 10 Watts

TO INSTRUMENT’S EXPOSED
METALLIC PARTS

Fig. 1.

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 29,5kV 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.
TX-28MD4 28,5kV ± 1kV.
TX-25MD4 28,2kV ± 1kV.
TX-21MD4 28kV ± 1kV.
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.

WATER PIPE

(

EARTH)

2

SERVICE HINTS

How to remove the rear cover

1. Remove the 9 screws as shown in Fig.2.

LOCATION OF CONTROLS

SCREWS

Fig.2.

E-BOARD

H-BOARD

Fig.3.

FOCUS
SCREEN

Y-BOARD

3

HOW TO MOVE THE CHASSIS INTO SERVICE POSITION

(A)

1. Remove the bead clamper from the mains lead and attach to the degauss coil, shown in Fig.5.

2. Hold and lift the rear of the E-PCB chassis and gently pull the chassis toward you, as shown in Fig.4.

3. Release the respective wiring clips and rotate the chassis horizontally through 90°, anti-cl ockwise.

4. Move the EHT lead around to the left side of the CRT neck.

5. Elevate the front of the chassis.

6. Clip the chassis frame onto the bead clamper, on the degauss coil, as shown in Fig.5.

7. Locate the base of the chassis frame into the hole (marked A), shown in Fig.6.

8. After servicing replace the bead clamper and ensure all wiring is returned to its original position before returning the
receiver to the customer.

Fig.5.

Fig.4.

Fig.6.

4

ADJUSTMENT PROCEDURE

The remote control is used for entering and storing adjustments, with the exception of Cut-off adjustments, which must
always be done prior to service adjustment. Perform adjustments in accordance with screen display. The display on the
screen also specifies the software version as well as the approx. setting values. The adjustment sequence for the service
mode is indicated below.

1. Set the Bass to maximum position, set the Treble to

minimum position, press the F button followed by the
volume down button on the customer controls at the
front of the TV and at the same time press the
"INDEX" button on the remote control, this will place
the TV into the Service Mode.

2. Press the RED / GREEN buttons to step up / down

through the functions.

NOTE: This TV also has the option of using a Memory Pack which enables you to copy the preset TV channels into the
Memory Pack and then download them onto this or any other EURO-4 TV set.

3. Press the YELLOW / BLUE buttons to alter the
function values.

4. Press the STR button after each adjustment has
been made to store the required values.

5. To exit the Service Mode, press the "N" button.

TV to Memory Pack process

1. Plug the memory pack into the AV1 21 pin terminal at
the back of the TV and switch the TV on.

2. Go into Service Mode as explained above.
The screen will show :-

Program
External>>TV

3. Press the BLUE button on the remote control.
The screen will show :-

Program
TV>>External

4. Press the STR button on the TV.
The screen will show :-

Please Wait

5. All the tuning information stored inside the TV will
now be transferred to the Memory Pack. This process
will take 2-3 minutes to complete and when finished
the screen will show :-

Complete

Memory Pack to TV process

1. Plug the memory pack into the AV1 21 pin terminal at
the back of the TV and switch the TV on.

2. Go into Service Mode as explained above.
The screen will show :-

Program
External>>TV

3. Press the STR button on the TV.
The screen will show :-

Please Wait

4. All the tuning information stored inside the Memory
Pack will now be transferred to the TV. This process
will take 2-3 minutes to complete and when finished
the screen will show :-

Complete

5. The tuning information from the Memory Pack has
now been copied into the TV.

6. To exit from the Service Mode press the "N" button.

7. The process has now been completed and the
Memory Pack can now be removed.

ERRORS

If an error occurs while using the Memory Pack the TV will detect this and the screen will show :-

Error !!

Error !!

If this happens then press the "N" button and repeat the process that was being used. If the errors continue to occur then
check the connectors between the TV and the memory pack and check the 9V battery inside the memory pack.

5

ADJUSTMENT PROCEDURE

Item / Preparation Adjustments
+B SET-UP

1. Receive a Greyscale signal.

2. Set the controls :­Brightness Minimum
Contrast Minimum
Volume Minimum

CUT OFF / Ug2 Test

1. Receive a Greyscale signal.

2. Degauss the tube externally.

3. Set the TV into Service Mode 1.

4. Select Cut off mode.

1. Set the +B voltage up as follows:­Adjust R811 so that B2 shows 148V±1V [130V±1V

TX-21MD4]

2. Confirm the following voltages.

B9 5 ± 0,25V B10 5 ± 0,25V
B5 12 ± 0,5V B11 33 ± 1,5V
B4 16 ± 1V B7 8 ± 0,5V
B12 26 ± 1V B8 5,5 ± 0,5V
B3 35 ± 1V B13 15 ± 1V
B1 200 ± 10V B14 -15 ± 1V

To adjust Cutoff connect an oscilloscope to the Blue
cathode, adjust "cutoff" value using the "Yellow" and "Blue"
buttons until the black level is 160V±5V press "STR" to store
the value. Remove the oscilloscope.
Select Ug2 adjustment and adjust the screen VR until the
display shows "O.K."

SELF CHECK

Self-check is used to automatically check the bus lines and hexadecimal code of the TV set. To get into the Self-Check mode
press the down (-/v) button on the customer controls at the front of the set, at the same time pressing the STATUS button on
the remote control, and the screen will show :-

VDP O.K.
TUN O.K.
E2 O.K.

PCB O.K.
Cab O.K.
Sum

Factory use only

MSP O.K.

--

OPTION 1 3D [3C]
OPTION 2 0C [0E]
OPTION 3 1D [1D]
OPTION 4 00 [00]
OPTION 5 EF [EF]
OPTION 6 23 [23]

If the CCU ports have been checked and found to be incorrect or not located then " - - " will appear in place of "O.K.".

Service Aids

To aid in the service of our current chassis there are a number of Service Aids which have been made available.

• LUCI interface kit (Linked Utility Computer Interface)
Part number: TZS6EZ002
This contains interface and cables for connecting TV service connector and a PC as well as diagnostic software. As new
models are introduced upgrade software will become available.

• VICI (Visual Interactive Computer Information)
These C.D.'s contain multimedia documentation providing quick access to service information.
Part No. TZS7EZ006 & TZS7EZ005

1. Service Manuals

2. Instruction Books

3. Technical Information

• TASMIN (Technically Advanced System for Multimedia Interactive Notes)
As well as providing a first step towards more interactive training this product also achieves quick access to Technical
Information.

6

WAVEFORM PATTERN TABLE

Vert Out
IC601 Pin 31

0.7V

H - Out
IC601 Pin 50

3V

HFLB
IC601 Pin 13

6.2V

20mS

64µS

Vert Drive
IC451 Pin 2

57V

H - Out
IC701 Pin 5

30mV

HFLB
IC701 Pin 8

1.5V

20mS

64µS

VFLB
IC451 Pin 3

1V

20mS

H - Pulse
Base Q503

2V

64µS

Video Out
IC601 Pin 59

2V

R - Out
IC601 Pin 37

275mV

R - Out
E8 Pin 5

4.6V

SCL
IC1201 Pin 3

64µS

64µS

64µS

G - Out
IC601 Pin 38

275mV

G - Out
E8 Pin 3

4.4V

SVM Out
IC601 Pin 34

64µS

64µS

64µS

64µS

B - Out
IC601 Pin 39

275mV

64µS

B - Out
E8 Pin 4

4.6V

64µS

3.7V
88mV

13µS

64µS

7

ALIGNMENT SETTINGS

(The figures below are nominal and used for representative purposes only.)

Alignment Function Settings / Special features

Horizontal Position

Vertical Position

Horizontal Amplitude

Vert. Amplitude

EW-amplitude

EW-amplitude

Trapezium-comp

Trapezium-comp

H-Pos

061

V-Pos

005

H-Amp

055

V-Amp

054

E/W-Amp1

-128

E/W-Amp2

006

Trapez-1

047

Trapez-2

-128

Optimum setting.

Optimum setting.

Optimum setting.

Optimum setting.

Optimum setting.

Optimum setting.

Optimum setting.

Optimum setting.

Vertical Linearity

Vertical Symmetry

DVCO

Cut-off DC

Ug2 Test

Highlight

Lowlight

Sub-Brightness

V-Lin

006

V-Sym

002

DVCO

-005

Cut-off

0171

Ug2

055

O.K.

High 0902 0777 0864
Low 0117 0132 0112

Sub-Brightness

255

Optimum setting.

Optimum setting.

Receive a PAL Colour Bar Pattern. For
DVCO alignment press "Blue" button, wait
until the colours are changing slowly and
press "STR".
To adjust Cutoff connect an oscilloscope to
the blue cathode, adjust "cutoff" value
using the "Yellow" and "Blue" buttons until

the black level is 160V±5V press "STR" to
store the value. Remove the oscilloscope.
Select Ug2 adjustment and adjust the
screen VR until the display shows "O.K."

Black Level

160V±5V
GND

Optimum setting.

Optimum setting.

8

VIDEO BLOCK DIAGRAM

,Q

Q352Q35





,Q

&



Q35

9

AV1

9LGHR2XW

%OXH

*UHHQ

5HG

9LGHR

AV2

9LGHR

$9

E - BOARD











Q105

Q104

61 V IN 1

43 B IN
42 G IN
41 R IN

62 VIN 2

63 VIN 3

60 C IN

VIN 4

64

IC601

VIDEO

PROCESSOR

VIDEO OUT
59

Q3601

SVM OUT 34

B OUT 39

G OUT 38

R OUT 37

B IN 47

G IN 46

R IN 45

TX-28MD4
TX-25MD4

ONLY

Q950 Q951

Q303

Q304

Q301

Q302

E8

TX-28MD4
TX-25MD4

ONLY

Q905 Q907 Q909

7

7

4

4

IC351

3

Q908Q906

7

Q353

VM

COILS

Y - BOARD

RGB

4

OUTPUT

2

1

8

9

3

3

5

5

Y2

CRT

1

2XW

9LGHR

AV3

Q3001

68
CVBS

IC1101

MICRO

PROCESSOR

R 37

G 38
B 39

E15

6

8

1

E61

H - BOARD

H1

6

8

1

H3

Q3402

IC3401

8

VIDEO

SWITCHING

6

3