Horizontal Oscillator Disable Circuit - Panasonic CT-32SX12F Service Manual

IMPORTANT: To protect against possible damage to
the solid state devices due to arcing or static discharge,
make certain that all ground wires 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 equipment 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 symbol
must be replaced with identical parts. Order parts from
the manufacturer's parts center using the parts
numbers shown in this service manual, or provide the
chassis number and the part reference number.
For optimum performance and reliability, all other parts
should be replaced with components of identical
specification.

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. DC ammeter
2. High voltage meter (0- 50kV electrostatic)
3. Variac or isolation transformer
4. HHS jig (see Fig. 2)
100Ω
TPD50
Figure 2. HHS jig
Service notes (continued)
on the schematic
1KΩ
TPD51
- 6 -
Preparation
1. Connect receiver to AC 120 Volts. Do not turn ON.
2. Connect HIGH VOLTAGE meter to 2nd anode
(H.V. button).
Note: Use cold ground(
3. Connect the ammeter serial from the flyback anode
lead to the picture tube anode socket.
4. Prepare HHS jig to be connected between TPD50
and TPD51 as shown in Fig. 2.
:
Procedure
1. Open connector A17.
2. Turn power ON and apply a white pattern.
3. Set current within 50-100µΑ by changing the
picture and bright controls.
4. Turn power OFF.
5. Connect HHS jig between TPD50 and TPD51 (VR
should be turn fully clockwise).
6. Turn power on.
7. Turn slowly the variable resistor to increase the
current until the horizontal sync frequency abruptly
increases indicating that the horizontal frequency is
just beginning to pull out of sync. Maintain the
current within 50-100µΑ by changing the picture
and bright controls
8. Observe the high voltage meter. HIGH VOLTAGE
should read less than 36kV.
9. Turn power OFF, remove HHS jig, HV meter,
ammeter and connect A17 connector.
10. Turn power ON.
BRIGHTNESS controls. Confirm B+ 140V±1.5V
with 120V AC applied.
Note: If high voltage is not within the specified
limit, the cause must be determined before
the receiver is returned to the owner.
) for negative lead.
Reset PICTURE and