Toshiba 50H81 Service Manual - Page 16

Circuit Checks, Voltage, Check, Caution, Circuit, Anode, Measuring, Method - power supply

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GENERAL ADJUSTMENTS SPECIFIC INFORMATIONS CIRCUIT CHECKS HIGH VOLTAGE CHECK CAUTION: There is no HIGH VOLTAGE ADJUSTMENT on this chassis. Checking should be done following the steps below. 1. Connect an accurate high voltage meter to the anode of the picture tube. 2. Turn on the receiver. Set the BRIGHTNESS and CONTRAST to minimum (zero beam current). 3. High voltage must be measured below (B) kV. Refer to table-1 for high voltage (B). (See SETTING & ADJUSTING DATA on page 17) 4. Vary the BRIGHTNESS to both extremes to be sure the high voltage does not exceed the limit under any conditions. CAUTION: When the following parts fail, check the High Voltage after replacing. Location No. T461 C407 C408 C441 C432 C433 Name Flyback Capacitor Capacitor Capacitor Capacitor Capacitor Descriptions 50" TFB3090AD 4700pF, ±3% 8200pF, ±5% 4700pF, ±5% 8200pF, ±5% 1200pF, ±3% ANODE VOLTAGE MEASURING METHOD CAUTION: Take extra precaution when measuring this high voltage. High voltages are also present in surrounding circuit boards (CRT DRIVE assembly, DEFLECTION assembly, and POWER SUPPLY assembly). 1. Disconnect the FBT anode cable as outlined below. Measure high voltage at the point where the cable enters the FBT. 2. Holding the rubber cover firmly, turn it counterclockwise and check that the lock has been disengaged. (See Fig. b on page 8.) 3. Determine the extent of the rubber cover before disconnecting the cable. 4. Pull straight up the anode cable to disconnect. 5. When reconnecting the cable, proceed in the reverse order. After reconnecting, tug on the cable to check that it is secure. FS CIRCUIT CHECK The Fail Safe (FS) circuit check is indispensable for the final check in servicing. Checking should be done following the steps below. 1. Turn the receiver on. 2. Temporarily short TP- (R) and TP- (X) on the DEF/POWER Board with a jumper wire. Raster and sound will disappear. 3. The receiver must remain in this state even after removing the jumper wire. This is the evidence that the FS circuit is functioning properly. 4. To obtain a picture again, temporarily turn the receiver off and allow the FS circuit more than 5 seconds to reset. Then turn the receiver on to produce a normal picture. Troubleshooting Guide for Fail Safe Circuit Check that the set returns to normal operation when pin 12 of Z801 is grounded with jumper wire. YES NO Check the voltage across Capacitor C419 is approximately (C) volts. Refer to table -4 for fall safe voltage (C) . Faulty power circuit or horizontal circuit. YES (See SETTING & ADJUSTING DATA on page 17) NO Defective Fail Safe Circuit - 16 -

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– 16 –
GENERAL ADJUSTMENTS
SPECIFIC INFORMATIONS
CIRCUIT
CHECKS
HIGH
VOLTAGE
CHECK
CAUTION:
There is no HIGH VOLTAGE ADJUSTMENT on
this chassis. Checking should be done following
the steps below.
1. Connect an accurate high voltage meter to the anode of
the picture tube.
2. Turn on the receiver.
Set the BRIGHTNESS and CON-
TRAST to minimum (zero beam current).
3.
High voltage must be measured below (B) kV.
Refer to table-1 for high voltage (B).
(See SETTING & ADJUSTING DATA on page 17)
4. Vary the BRIGHTNESS to both extremes to be sure the
high voltage does not exceed the limit under any condi-
tions.
CAUTION:
When the following parts fail, check the High Voltage after
replacing.
FS
CIRCUIT
CHECK
The Fail Safe (FS) circuit check is indispensable for the final
check in servicing.
Checking should be done following the
steps below.
1.
Turn the receiver on.
2.
Temporarily short TP- (R) and TP- (X) on the DEF/POWER
Board with a jumper wire.
Raster and sound will disappear.
3.
The receiver must remain in this state even after removing
the jumper wire.
This is the evidence that the FS circuit is
functioning properly.
4.
To obtain a picture again, temporarily turn the receiver off
and allow the FS circuit more than 5 seconds to reset.
Then
turn the receiver on to produce a normal picture.
Location
No.
Name
50"
T461
C407
C408
C441
C432
C433
TFB3090AD
4700pF,
±
3%
8200pF,
±
5%
4700pF,
±
5%
8200pF,
±
5%
1200pF,
±
3%
ANODE
VOLTAGE
MEASURING
METHOD
CAUTION: Take extra precaution when measuring this high
voltage. High voltages are also present in
surrounding circuit boards (CRT DRIVE assem-
bly, DEFLECTION assembly, and POWER
SUPPLY assembly).
1.
Disconnect the FBT anode cable as outlined below. Meas-
ure high voltage at the point where the cable enters the
FBT.
2. Holding the rubber cover firmly, turn it counterclockwise
and check that the lock has been disengaged. (See Fig. b
on page 8.)
3.
Determine the extent of the rubber cover before discon-
necting the cable.
4.
Pull straight up the anode cable to disconnect.
5.
When reconnecting the cable, proceed in the reverse order.
After reconnecting, tug on the cable to check that it is se-
cure.
Troubleshooting Guide for Fail Safe Circuit
Check that the set returns to normal operation when
pin 12 of Z801 is grounded with jumper wire.
Check the voltage across
Capacitor C419 is
approximately (
C)
volts.
Refer to table –4 for
fall safe voltage (
C)
.
Faulty power
circuit or hori-
zontal circuit.
Defective Fail Safe Circuit
(See SETTING & ADJUSTING
DATA on page 17)
YES
NO
NO
YES
Descriptions
Flyback
Capacitor
Capacitor
Capacitor
Capacitor
Capacitor