Sharp 27F640, Service Manual

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5
27F640
27F641
CIRCUIT PROTECTION
The receiver is protected by a 4.0A fuse (F701),
mounted on PWB-A, wired into one side of the AC
line input.
X-RADIATION PROTECTOR CIRCUIT TEST
After service has been performed on the horizontal
deflection system, high voltage system, B+ system,
test the X-Radiation protection circuit to ascertain
proper operation as follows:
1. Apply 120V AC using a variac transformer for accurate
input voltage.
2. Allow for warm up and adjust all customer controls
for normal picture and sound.
3. Receive a good local channel.
4. Connect a digital voltmeter to TP653 (P651 Pin3) and
make sure that the voltmeter reads 13.85
±
0.6V DC.
5. Apply external 17.3V DC at TP653 by using an
external DC supply, TV must be shut off.
6. To reset the protector, unplug the AC cord (about
1min.) and plug the AC cord power on. Now make
sure that normal picture appears on the screen.
7. If the operation of the horizontal oscillator does not
stop in step 5, the circuit must be repaired before the
set is returned to the customer.
HIGH VOLTAGE CHECK
High voltage is not adjustable but must be checked
to verify that the receiver is operating within safe
and efficient design limitations as specified checks
should be as follows:
1. Connect an accurate high voltage meter between
ground and anode of picture tube.
2. Operate receiver for at least 15 minutes at 120V AC
line voltage, with a strong air signal or a properly tuned
in test signal.
3. Enter the service mode and select the service
adjustment "V11" and Bus data "01" (Y-mute on, CRT
Cut Off).
4. The voltage should be below 31.5kV (at zero beam).
If a correct reading cannot be obtained, check circuitry
for malfunctioning components. After the voltage test,
make Y-mute off to the normal mode.
INSTALLATION AND SERVICE INSTRUCTIONS
Note: (1) When performing any adjustments to resistor controls and transformers use non-metallic
screwdrivers or TV alignment tools.
(2) Before performing adjustments, the TV set must be on at least 15 minutes.