Panasonic CT-25G5B Schematic

ORDER NO. MTNC000664A1 B5

Service Manual

Color Television

Main Manual

(NA6LV)

Panasonic

Models

CT-25G5B AP356M CT-25G5UB AP356M

This Simplified Service Manual is issued to add listed models to the main Service Manual order No. MTNC000146C1(CT-27G 5B/CB /UB). A full set of Sc hematics , Pict ures and a c omplete Parts List are in clude d in this Simplified Manual. Please file and use this Service Manual together with the Main Service Manual, order No. MTNC000146C1(CT-27G5B/CB/UB).

“WARNING! This Service Manual is desig ned for expe rienced repa ir technici ans only and is not de signed for u se by the general pub lic. It does not contain warnings or cautions to advise non-technical individuals of potential dangers in attempting to service a product. Products powered by electricity should be serviced or repai red only by exp erienced profe ssional techn icians. Any attemp t to service or repair the product or products dealt with in this Service Manual by anyone else could result in serious injury or death.”

Chassis

The service technician is required to read and follow the “Safety Precautions” and “Important Safety Notice” in this Main Manual.

and distribution is a violation of law.

Important Safety Notice

Special components are used in this television set which are important for safety. These parts are identified on the schematic diagra m by the s ymbol and printed in BOLD TYPE on the repl aceme nt part list. It is esse ntial tha t

these critical parts are replaced with the manufacturer’s specified replacement part to prevent X-ray radiation, shock, fire or other hazards. Do not modify the original design without the manufacturer’s permission.

Safety Precautions

General Guidelines

An Isolation Transformer should always be used during the servicing of a r eceiver whose c hassis is not isolated from AC power line. Use a transformer of adequate power rating as this protects the technician from accidents resulting in personal injury from electrical shocks. It will also pr otect the Receiver from being damaged by accidenta l shorting that may occur during servicing. When servicing, observe the original lead dress, especially in the high voltage circuit. Replace all damaged parts (also parts that show signs of overheating.) Always Replace Protective Devices, such as fishpaper, isolation resistors and capacitors, and shields after servicing the Receiver. Use only manufacturer’s recommended rating for fus es, circuits breakers, etc. High potentials are present when this Receiver is operating. Operation of the Receiver without the rear cover introduc es danger for el ectrical sho ck. Servicin g should not be performed by anyone who is not thoroughly familiar with the necessary precautions when servicing high-voltage equipment.

Extreme care should be p ra ctic ed wh en Handling the Picture Tube. Rough handling may cause it to implode

due to atmospheric pres sure. (14.7 lbs per sq. in.). D o not nick or scratch the glass or subject it to any undu e pressure. When handling, use safety goggles and heavy gloves for protection. Discharge the picture tube by shorting the anode to chassis ground (not to the cabinet or to other mounting hardware). When discharging connect co ld ground (i .e. dag groun d lea d) to the anode with a well insulated wire or use a grounding probe. Avoid prolonged exposure at close range to unshielded areas of the picture tube to prevent exposure to X-ray radiation. The Test Picture Tube used for servicing the chas sis at the bench should incorporate safety glass and magnetic shieldi ng. The safety glass pr ovide shielding for the tube viewing area against X-ray radiation as well as implosion. T he magnetic shield lim its the X-ray radiation around the bell of the pict ure tube in addition to the restricting magnetic effects. When using a picture tube test jig for service, ensure that the jig is capable of handling 37.69kV without causing X-ray radiation. Before returning a ser viced receiver to the owner, the service technic ian must thoroughly test the unit to ensure that is completely safe to operate. Do not use a

line isolation transformer when testing.

Leakage Current Cold Check

Unplug the AC cord and connect a jumper between the two plug prongs. Measure the re si stance betw e e n th e j um p ere d AC pl ug and expose metallic parts such as screwheads, antenna terminals, control shafts, etc. If the exposed

metallic part has a return path to the chassis, the reading should be between 240kΩ and 5.2MΩ. If the exposed metallic part does not have a return path to the chassis, the reading should be infinite.

Leakage Current Hot Check (Fig. 1)

Plug the AC cord directly into the AC outlet. Do not use an isolation transformer during the check. Connect a 1.5kΩ 10 watt resistor in parallel with a

0.15µF capacitor between an exposed metallic part and ground. Use earth ground, for example a water pipe. Using a DVM with a 1000 ohms/volt sensitivity or higher, measure the AC potential across the resistor. Repeat the procedure and measure the voltage present with all other exposed metallic parts. Verify that any potential does not exceed 0.75 volt RMS. A leakage curr ent test er (suc h a S impson M odel 229, Sencore Model P R57 or equival ent) may be used in the above procedure, in which case any current measure must not exceed 1/2 milliamp. If any measurement is out of the specified limits, there is a possibility of a s hoc k haz ard and the Receiver mus t b e repaired and rechecked before it is returned to the customer.

AC VOLTMETER

COLD WATER PIPE (GROUND)

0.15µF

TO INSTRUMENT’S EXPOSED METAL PARTS

1500Ω,10 W

Figure 1. Hot Check Circuit

X-ray Radiation

WARNING: T he potential source of X-ray radiation in the

TV set is in the High V ol tage sect ion and th e picture tu be.

Note: It is important to use an accurate, calibrated

high voltage meter.

Set the brightness, picture, sharpness and color controls to Minimum. Measure the High Voltage. The high voltage should be 29.25kV ± 1.25kV. If the upper limit is out of tolerance, immediate service and correction is required to insure safe operation and to prevent the possibility of premature component failure.

Horizontal Oscillator Disa ble Circuit Test

This test must be performed as a final check before the Receiver is returned to the customer. See Horizontal Oscillator Disable Circuit Procedure Check in this manual.

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Important Safety Notice . . . . . . . . . . . . . . . . . . .2

Safety Precautions. . . . . . . . . . . . . . . . . .2

Service Notes . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Horizontal Oscillator Disable Circuit. . . . .5

Receivers Feature Table. . . . . . . . . . . . . . . . . . .6

Location of Controls (Receiver)

Receiver Front Control Panel. . . . . . . . . .7

Location of Controls (Remote)

EUR501450 . . . . . . . . . . . . . . . . . . . . . . .8

Component Identification. . . . . . . . . . . . . . . . . .9

Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

SCHEMATICS AND VOLTAGES

A-Board . . . . . . . . . . . . . . . . . . . . . . . . Sheet-1A

C-Board . . . . . . . . . . . . . . . . . . . . . . . . Sheet-1B

WAVEFORMS. . . . . . . . . . . . . . . . . . . . . Sheet-1B

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Service Notes

Chip Components

TRANSISTOR

CAPACITOR

RESISTOR

MH DIODE

SOLDER CAPS

1ST DIGIT

2ND DIGIT

MULTIPLIER =1600 = 1.6k

GRADE

TYPE

COMMON

ANODES

CATHODE

Note: These components are affixed with glue. Be careful not to break or damage any foil under the

component or at the pins of th e ICs when removing. Usually applying heat to the component for a short time while twisting with tweezers will break the component loose.

Leadless Chip Component (surface mount)

Chip components must be replaced with identical chips due to critical foil tr ack spacing. There are n o holes in the board to mount standard transistors or diodes. Some chips capacitor or resistor board solder pads may have holes t hrough the board, however the hole diameter limits standard resistor replacement to 1/8 watt. Standard capacitor may also be limited for the same reason. It is recommended that identical components be used. Chip resistor have a three digit numerical resistance code - 1st and 2nd significant digits and a multiplier. Example: 162 = 1600 or 1.6kΩ resistor, 0 = 0Ω (jumper). Chip capacitors generally do not have the value indicated on the capacitor. The color of the co mponent indicates the general range of the capaci tance. Chip transistors are id enti fie d b y a two letter code. The first letter indicates the type and the second lette r, the grade of transistor. Chip diodes have a two lette r i den tif icati on c ode as per the code chart an d are a dual diode pack with either common anode or common cathode. Check the parts list for correct diode number.

Component Removal

1. Use solder wick to remove s older from compo nent end caps or terminal.

2. Without pulling up, carefully twist the component with tweezers to break the adhesive.

3. Do not reuse removed leadless or chip components since they are subject to stress fracture during removal.

Chip Component Installation

1. Put a small amount of solder on the board soldering pads.

2. Hold the chip component against the soldering pads with tweezers or with a miniature alligator clip and apply heat to the pad area with a 30 watt iron until solder flows. Do not appl y heat for more than 3 seconds.

How to Replace Flat-IC

- Required Tools -

• Soldering iron • De-solder braids

• Iron wire or small awl • Magnifier

1. Remove the solder from all of the pins of a Fla t-IC by using a de-solder braid.

De-Solder

Flat-IC

2. Put the iron wire under the pins of the Flat-IC and pull it in the direction indicated while heating the pins using a soldering iron. A small awl can be used instead of the iron wire.

Iron Wire

Pull

Soldering Iron

3. Remove the solder from all the pads of the Fla t-IC by using a de-solder braid.

Soldering Iron

De-Solder Braid

Flat IC

4. Position the new Flat-I C in place (app ly the pins of the Flat-IC to the soldering pads where the pins need to be soldered). Properly determine the positions of the soldering pads and pins by correctly aligning the polarity symbol.

Polarity Symbol

Braid

Awl

123.........

5. Solder all pins to the soldering pads using a fine tipped soldering iron.

Solder

Soldering Iron

6. Check with a magnifier for solder bridge between the pins or for dry joint between pi ns and sold erin g pads. To remove a solder bridge, use a de-s older braid as shown in the figure below.

De-Solder Braid

Solder Bridge

Soldering Iron

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Service Notes (Continued)

IMPORTANT: To protect against possible damage to

the solid state devices due to arcing or static discharge, make cer tain that all g round wir es a nd CTR DAG wire are securely connected.

CAUTION: The power supply circuit is above earth ground and the chassis cannot be polarized. Use an isolation transformer when servicing the Receiver to avoid damage to the test equipmen t or to the chassis. Connect the test equipment to the proper ground ( ) or

( ) when servicing, or incorrect voltages will be measured.

WARNING: This Receiver has been designed to meet or exceed applicable safety and X-ray radiation protection as specified by government agencies and independent testing laboratories.

To maintain original product safety design standards relative to X-ray radiation and shock and fire hazard,

parts indicated with the s ymbol on the schematic must be replaced with identical parts. Order parts from

the manufacturer’s parts center using the parts numbers shown in t his service manual, or provide the chassis number and the part reference number.

For optimum perfo rmance and reliab ility, all other parts should be replaced with components of identical specification.

Procedure:

1. Tune in a station to verify that the horizontal is in sync.

2. Obtain a Monoscope pattern or a signal generator crosshatch pattern

3. Connect the voltmete r (-) lead to T PD2 an d the (+) lead to TPD1 (junction of D555 anode, R556 & R557). Set Bright level to (0 ) an d Picture for a 1.8 volt reading on the voltmeter.

4. Turn the Receiver OFF. Connect a jumpe r across IC803 pin 3 and pin 4. Apply +9 V DC to cathode of D001.

5. Reduce the AC supply voltage to approximately 45V. Connect the high voltage meter to the CRT anode. (H.V. button).

Note: Use the Dag Ground (C10 on the CRT Board)

to connect the (-) lead of the meter.

6. Turn the Receiver ON. Slowly increase the AC supply voltage and verify that the high voltages does not exceed 37.1kV when horizontal; just begins to pull ou t of sync . If the hig h voltage is no t within the specified limit, the cause must be determined and corrected before the Receiver is returned to the customer.

Horizontal Oscillator Disable Circuit

This chassis employs a special circuit to protect against excessive high voltage and beam current. If, for any reason, the high voltage and beam current exceed a predetermined level this protective circuit activates and detunes the horizontal oscillator that limits the high voltage. The over-voltage protection circuit is not adjustable. However, if components indicated by the

symbol on the schematic in either the horizontal sweep system or the over-voltage protection circuit

itself are changed, the operation of the circuit should be checked using the following procedure:

Equipment needed to check the disabled circuit:

1. Voltmeter (0 - 200V scale)

2. High Voltage Meter (0- 50kV)

3. Variac or Isolation Transformer

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Receiver Feature Table

FEATURE\MODEL CT-25G5B/UB

Chassis NA6LV T un ning sys tem 40K # of channe ls 181 Menu language Eng/Span/Fr Closed Caption X V-Chip X 75 Ω input X Remote Model # EUR501450 Picture tube A63QDB891X Notch filter P V/A norm V AI Sound X Built-in audio power 1.5Wx2 (10%) # of speakers 2 A/V in (rear/front) 2(1/1) Dimensions mm

(WxDxH) in Weight (kg/lbs) 34.25/75.35 Power source (V/Hz) 120/60 Anode voltage 29.25kV ± 1.25kV Video input jack Audio input jack 500mV RMS 47kΩ A-Board TNP2AH018 AB C-Board TNP2AA062 AD

600x665x634

23.62x26.18x24.96

75Ω, phono jack

p-p

Table 1. Receiver Features

Specifications are subject to change without notice or obligation. Dimensions and weights are approximate.

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