Magnum CTV-2120 TXT User manual

MODEL:
SERVICE MANUAL
CTV-2120 TXT
TV SET

2
SAFETY INSTRUCTIONS
WARNING: BEFORE SERVICING THIS CHASSIS, READ THE "X-RAY
RADIATION PRECAUTION", "SAFETY PRECAUTION" AND "PRODUCT SAFETY
NOTICE" DESCRIBED BELOW.
X-RAY RADIATION PRECAUTION
1. Extremely high voltage of the picture tube may result in producing potentially hazardous X-RAY RADIATION. To
avoid such hazards, the high voltage must not be above the specifiedlimit.
The nominal value of the high voltage of this receiver is about 25.9 kV at zero beam current (minimum brightness)
under 175-245V AC power source.
The high voltage must, under any circumstances, not exceed about 30.5 kV.
Each time this receiver requires servicing, the high voltage should be checked according to the HIGH VOLTAGE
CHECK procedure at the back of this manual. it is recommended to record the reading of the high voltage in the
service record each time. Using an accurate and reliable high impedance and high voltage meter is quite important.
Connect the NEGATIVE and POSITIVE probe of a high voltage meter to the "ground" and the high voltage anode
cap of the picture tube respectively.
HIGH VOLTAGE CHECK CONNECTION DIAGRAM
2. The only source of X-RAY RADIATION in this receiver is the picture tube. For ensuring the intensity of X-RAY
RADIATION from the picture tube being within the specified safety limit, the replacement picture tube must be
exactly the same type specified in the parts list.
3. Some parts in this receiver have special safety-related characteristicswhich would affect X-RAY RADIATION
protection. For safety, parts replacement should be carried out only after referring to the "PRODUCT SAFETY
NOTICE" below.
PRODUCTSAFETY NOTICE
Many electrical and mechanical parts in this receiver have special safety-related characteristics (directly relate to
high voltage, high temperature or electric shock) which are not easily seen by visual inspection. Whenever replacing
such components, make sure that the replacement parts can provide effective X-RAY RADIATION protection even
though their high voltage and wattage can meet the specification of the original design. Such parts can be identified by
shading and marking with in the schematic diagram and the parts list.
Before replacing any of these components, read the parts list in this manual carefully. Using substitute parts which do
not have the same safety characteristics as the ones specified in the parts list may create excessive X-RAY RADIATION.
I2C BUS CONCEPT
(1). Characteristics
1.1 I2C Bus consists of clock (SCL) and data (SDA) lines.
1.2 It transmits data among integrated circuits in full duplex mode.
1.3 It is composed of a main IC chip (CPU) and one or more sub-IC chips.
lThe CPU mainly operates data transmissions and also generates clock signal.
lThe CPU also controls all sub-IC chips, making them work.
(2). I2C Bus Application in this TV unit
High impedance and high voltagh meter Chassis Picture tube ground
Picture tube high voltage anode cap

3
SDA
SCL
SDA
SCL
SDA
SCL
In this TV unit, IC801 is the main chip while IC802, IC201 and other chips are regarded as sub-chips.
2.1 IC801 (CPU) controls the functions of IC201 via the I2C bus between them.
2.2 The data of channel positions, BT voltage, band, AFT, clear, volume, power on/off, timer, color, etc. are written
into, stored in and read out from IC802 via the I2C bus.
SAFETY PRECAUTION
1.High voltage of 24-26 kV is always present inside this receiver when it is operating, so be cautious of electric shock
hazard while removing the back cabinet to process adjustment.
(A) Servicing should not be attempted by any person who is not very familiar with the required re-cautions when
working on this high-voltage equipment.
(B) Before removing the anode cap of the picture tube, discharge the high voltage potential from the picture tube
anode several times by short-circuiting the anode together with its ground tokeep off electric shock hazard.
(C) Perfectly discharge the high voltage potential of the picture tube before handling the picture tube which is
highly evacuated. When it is broken, danger may be caused because of the violent burst of its glass fragments.
2. If the fuse in this receiver is blown, replace it with the type specified in the chassis parts list or with the same
specifications (never use other types).
3. Whenever replacing with new components, twist the lead wires of the component together with the concerned
residual leads before soldering.
4. Whenever replacing with a new high wattage resistor (such as oxide metal filmresistor) on any of the circuit boards,
keep the body of the resistor 10 mm above the circuit board.
5. Keep all connecting wires away from the components of high voltage or high temperature.
6. This receiver is designed to operate at AC 175-245V~50/60Hz, NEVER connect to DC supply or any other power
sources.
7. The main chassis of this receiver is perfectly isolated.
INSTALLATION AND SERVICE ADJUSTMENTS
GENERAL INFORMATION:
Normally, this receiver have been thoroughly checked and adjusted before leaving the factory; therefore it should
operate normally and produce perfect color and B/W pictures upon installation. However, several minor adjustments
may be required according to the practical situation.
This receiver is packed in a cardboard carton during transportation. Carefully draw it out from the carton and remove
all packing materials.
Plug the receiver's power cord into a convenient 175-245V 50/60Hz AC two pinsor three pins power outlet.
Check and adjust all the customer controls such as BRIGHTNESS, CONTRAST and COLOUR to obtain natural color or
B/W picture.
AUTOMATIC DEGAUSSING :
A degaussing coil is mounted around the picture tube so that external degaussing after moving the receiver is
normally unnecessary, providing the receiver is properly degaussed upon installation. The degaussing coil operates for
about 1 second after the power to the receiver is switched ON. If the set is moved or faced in a different direction, the
power switch must be switched off at least one hour in order that the automatic degaussing circuit operates properly.
And then the receiver turned it again.
Should the chassis or parts of the cabinet become magnetized to cause poor colour purity, use an external degaussing
coil. Slowly move the degaussing coil around the faceplate of the picture tube, the sides and front of the receiver and
slowly withdraw the coil to a distance of about 2 meters before disconnecting it from AC source. If colour shading still
persists, perform the “COLOUR PURITY ADJUSTMENT” and “CONVERGENCE ADJUSTMENTS” procedures as
mentioned later.

4
Remote Handset Operation
Top View of Remote Control
HOW TO OPERATE REMOTE CONTROL
There are 27 buttons on the remotecontrol. It operates with infra-red beam which is not affected by noise or other
interferences. Make sure strong light never strikes on the infra-red receiver; otherwise, it would obstruct the remote
control working normally with the TV unit.
Do not drop or expose it to high temperature.
*4 (FOR NICAM/ GERMAN STEREO ONLY) *15-27 (FOR TELETEXT ONLY)
1. SOUND MUTING BUTTON
2. NUMBER (0-9) BUTTONS
3. STATUS (RED) BUTTON
4. NICAM BUTTON
5. PERSONAL PREFERENCE (GREEN) BUTTON (PP)
6. MENU BUTTON
7. VOLUME (UP/DOWN) BUTTONS
8. STANDBY BUTTON
9. DIGITSELECTBUTTONS
10. TV/AV BUTTON
11. PREVIOUS (YELLOW) BUTTON
12. ANALOG BUTTON
13. SLEEP (BLUE) BUTTON
14. PROGRAM (UP/DOWN) BUTTONS
15. CANCEL BUTTON
16. SUBCODE BUTTON
17. STOP BUTTON
18. REVEAL BUTTON
19. TV/TXT. BUTTON
20. INDEX BUTTON
21. MIX. BUTTON
22. SIZE BUTTON
23. DIGIT ENTRY (0-9) BUTTONS
24-27.COLOUR BUTTON
HOW TO DISASSEMBLE REMOTE CONTROL HAND UNIT (see Fig. 1)
1. Remove the battery cover and loosen the screws.
2. Open one side of the back cabinet to take it away from the front cabinet.
Fig. 1
REVEAL
SUBCODE
PP
AV
STOP
CANCEL
VOL
P
P
VOL
STATUS
NIACM ANALOG
SIZE
INDEX
SLEEP
MIX
TV/TXT
RECALL
+
+
-

5
METHOD OF REMOVING BACK CABINET(see Fig. 2)
Attn.: Before disassembling the back cabinet, first draw the power cord plug of the receiver from AC outlet.
1. Disconnect the antenna cable from the antenna terminal.
2. Loosen the 5pieces of screw (A) used in fixing the antenna jack plate on the back cabinet.
3. Loosen the 9pieces of screw (B) used in fixing the back cabinet to the front cabinet; thenremove the back cabinet.
Screws(B)
Screws(B)
Screws(A)
Fig.2
METHOD OF REMOVING PICTURE TUBE(see Fig. 4)
After taking out the chassis holder (main chassis), proceed the following procedures accordingly:
1. Turn the receiver down and let the screen of the picture tube face downward, and put it on a soft cushion.
2. Loosen the 4 pieces of nut used in fixing the picture tube on the front cabinet, remove the degaussing coil; then use
two hands to hold the edges of the picture tube tightly and draw it out.
3. Detach the ground wire of the picture tube which is attached to thelugs of the picture tube with springs.
Fig.4
SUGGESTION: Before servicing the chassis, please read through “X-RAY RADIATION PRECAUTION",
"SAFETY PRECAUTION" and "PRODUCT SAFETY NOTICE" atPage 2& 3of this manual.
GENERAL ADJUSTMENT INSTRUCTIONS
This receiver is transistorized and special care should be taken when servicing. If not necessary, do not attempt any
adjustments because the requirements of the procedures are very stringent. Read the following matters before
attempting any adjustments.
An isolation transformer should be used during any dynamic service to avoid possible electricshock hazard.
The test equipment specified or their equivalent is required in having proper alignment. Using unsuitable equipment,
which do not meet these requirements, may result in improper alignment.
Correct matching of the equipment is essential. Failure of using proper matching will result in responses which cannot
show the true operation of the receiver.
Excessive signal by using a sweep generator can cause the receiver circuit overloaded. Overloading should be avoided
to obtain a true response curve. Insertion of markers by using the marker generator should not cause the response
curve distorted.