Sony CTV-25R1 Manual page 101

4. The normal voltage should be less than 0.5Vdc. If it is less than
0.5Vdc before the TV turns OFF again, there is a problem in the
protection circuit at Q300 or IC301.
Test Q300 for leakage or replace.
Move your DVM probe to IC301/pin 18 and turn ON the TV. If this
voltage stays below 2Vdc, Q300 is leaky. If above 2Vdc, IC301 may
be defective.
5. If the voltage at Q300's base is HIGHER than 0.5Vdc, the problem
may be in IC521, Q571, or in the circuitry.
6. Place your DVM at IC521/pin 7 and turn ON the TV. The normal
voltage should be less than 2Vdc. If it is higher, the problem is around
IC521 or there is excessive FBT voltage from an open safety capaci-
tor (C508) or high B+ voltage.
Reduce the AC voltage and monitor the voltages at IC521/pins 5 &
6. The voltage at IC521/pin 6 is fixed at the D573 zener voltage
plus 0.6V (D572). The normal voltage at pin 5 should never ex-
ceed 10Vdc.
If the voltage at IC521/pin 5 is HIGHER than 10Vdc, the problem is in
the circuit's safety capacitor or high B+ voltage.
If the voltage at IC521/pin 5 is Lower than 10Vdc, the problem is
about IC521.
7. If none of the voltages around IC521 were high, the problem must be
around Q571, a defective horizontal output transistor or transformer.
8. Place your DVM at Q571/collector. Turn the TV ON. This voltage
should not rise above 10Vdc.
If this voltage is HIGH, suspect Q571, R571 and other resistors in the
area.
If these protection parts test OK, there is a heavy current demand on
the B+ line. The problem may be a short at the FBT secondary wind-
ings.
97
Timer / Standby light – blinks four times
A vertical deflection failure or horizontal drive failure is indicated.
1. Test the horizontal section by using one of these tricks:
•
Place your scope probe by the FBT and turn ON the TV. You will
see the horizontal signal if the drive path from the Jungle IC to
the FBT is OK
• Listening to the frying sound at the yoke is another indicator of
horizontal signal arriving at the yoke
2. Test the vertical stage by using the scope probe to monitor the verti-
cal drive signal and the DVM to measure the positive and negative
supply voltages to the vertical IC541 at turn ON.
3. Test the Protection circuitry by placing your scope lead at the Vertical
Output IC541/pin 3. You should see a 30Vp-p pulse there. If it is
present, this pulse is not getting to IC001/pin 17. Replace zener
D001 if shorted.
Timer / Standby light – blinks five times
This failure is caused by a problem in the video output IK circuit. Turning
up the screen control will let you see light on the screen so you can make
an evaluation of the problem. For more details see the Video Output
section of this training manual.