Philips H8 - Troubleshooting Flow Charts

DEAD SET/
SHUTDOWN
IS 135 VOLTS (VBAT)
PRESENT ON THE CATHODE
OF DIODE 6938?
DOES A VOLTAGE APPEAR
MOMENTARILY ON THE CATHODE
OF 6938 WHEN POWER IS
APPLIED TO THE SET?
NO
IS A SMALL VOLTAGE
PRESENT ON THE
CATHODE OF 6941?
NO
CHECK FOR A SHORT
ON THE VBAT (135V)
LINE.
YES
IS 130 TO 160 VOLTS
PRESENT ON PIN 3 OF 7921?
THIS IS RELATIVE TO HOT
GROUND.
NO
IS THE VOLTAGE ON PIN 4
OF 7921 CHANGING
BETWEEN 11 AND 16
VOLTS?
YES
IS A VOLTAGE > 16
VOLTS PRESENT ON
PIN 4 OF 7921?
NO
CHECK 7921, 2919,
AND RELATED
COMPONENTS.
YES
CHECK 7921, 6921, 3914,
3913, AND RELATED
COMPONENTS.
NO
IS DRIVE SIGNAL
PRESENT ON PIN 3
OF 7921?
YES
CHECK 7921.
NO
CHECK 5912, 3924,
3929, 6929, 3923, 7929,
AND RELATED
COMPONENTS.
YES
DOES THE STAND-BY LINE
GO LOW WHEN THE POWER
BUTTON IS PRESSED?
YES
DOES THE 8 VOLT
SUPPLY TURN ON?
YES
CHECK 7944, 7942,
AND RELATED
COMPONENTS.
NO
DOES THE 5 VOLT
SUPPLY TURN ON?
YES
CHECK 7967 AND
RELATED
COMPONENTS.
NO
IS HORIZONTAL
(LINEDRIVE1)
PRESENT?
YES
REPLACE THE SMALL
SIGNAL BOARD (SSB)
NO
IS HIGH VOLTAGE
PRESENT?
YES
CHECK 7481, 7410,
5431, AND RELATED
COMPONENTS.
NO
IS THE VERTICAL
FEEDBACK PULSE
PRESENT WHEN THE
SET IS TURNED ON?
YES
IS +13 VOLTS DC
PRESENT ON PIN 2 OF
7501 WHEN THE SET IS
TURNED ON?
NO
CHECK 3448, 3449,
AND RELATED
COMPONENTS.
NO
IS -13 VOLTS DC
PRESENT ON PIN 4 OF
7501 WHEN THE SET IS
TURNED ON?
YES
CHECK 3446, 3447,
AND RELATED
COMPONENTS.
NO
IS VERTICAL DRIVE
PRESENT ON PIN 7 OF
7501?
YES
REPLACE THE SMALL
SIGNAL BOARD (SSB).
NO
CHECK 7501, YOKES,
AND RELATED
COMPONENTS.
YES
IS THE 3.3 VOLT
STANDBY VOLTAGE
PRESENT?
NO
CHECK 7965 AND
RELATED
COMPONENTS.
NO
IS THE FRONT
DETECT LINE < 1
VOLT DC?
YES
CHECK 7991, 7990,
AND RELATED
COMPONENTS.
YES
DOES THE KEYBOARD LINE
(PIN 2 OF 0226 CHANGE TO 0.66
VOLTS WHEN THE POWER
BUTTON IS PRESSED?
NO
CHANGE THE SMALL
SIGNAL BOARD (SSB).
YES
CHECK THE
KEYBOARD AND
CONNECTIONS.
NO
A
YES
CHECK 7921, FUSE
1900, BRIDGE 6915,
AND RELATED
COMPONENTS.
NO
DOES APPROX 14 VOLTS
APPEAR MOMENTARILY
ON THE CATHODE OF
6941?
YES
CHECK FUSE 1941 AND
RELATED
COMPONENTS.
NO
CHECK THE FEEDBACK PATH,
7929, 7971, AND RELATED
COMPONENTS.
YES
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