AndrzejM
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tda4605
1. After applying mains supply, one can hear that the SMPS starts and stops regularly.
2. After disconnecting +120V from the SMPS transformer (the voltage for horizontal deflection circuits), SMPS starts up, and the POWER ON LED is on.
3. All elements in horizontal deflection seems to be OK. But to be sure all elements in +120 V rectifier area (BU508, diode, inductance and two 47uF/160V capacitors) have been replaced but without the positive effect.
4. This lead to the conclusion that the fault was in the TDA4605 based switching mode power supply.
5. There was 300V at the 220uF/385V capacitor at the input of the power supply (measured by digital multimeter) but additionally I have tested the 300V by the oscilloscope and I noticed very short negatives pulses there.
| ~ 1sec. |
______________________________ - 300V
||||| |||||
|| || || |
| | | | |
- 250V
SOLUTION:
The 220uF / 385V capacitor ((the one the rectified mains supply is applying to) was faulty.
Instead of nominal 200uF it has only 1uF. This 1uF was enough to start up the power supply under condition, that the load is below nominal value (without the deflection circuit). When rectifying diode, 100uF / 120V capacitor + 27kom discharge resistor were connected the transient task of charging 100uf capacitor was to heavy heavy for SMPS to start.
Because the problem concerns SMPS the type of equipment the problem appeared is insignificant, but as pure formality here are the details:
TV set “Curtis” OTVC 2501, capacitor reference : C665 .
1. After applying mains supply, one can hear that the SMPS starts and stops regularly.
2. After disconnecting +120V from the SMPS transformer (the voltage for horizontal deflection circuits), SMPS starts up, and the POWER ON LED is on.
3. All elements in horizontal deflection seems to be OK. But to be sure all elements in +120 V rectifier area (BU508, diode, inductance and two 47uF/160V capacitors) have been replaced but without the positive effect.
4. This lead to the conclusion that the fault was in the TDA4605 based switching mode power supply.
5. There was 300V at the 220uF/385V capacitor at the input of the power supply (measured by digital multimeter) but additionally I have tested the 300V by the oscilloscope and I noticed very short negatives pulses there.
| ~ 1sec. |
______________________________ - 300V
||||| |||||
|| || || |
| | | | |
- 250V
SOLUTION:
The 220uF / 385V capacitor ((the one the rectified mains supply is applying to) was faulty.
Instead of nominal 200uF it has only 1uF. This 1uF was enough to start up the power supply under condition, that the load is below nominal value (without the deflection circuit). When rectifying diode, 100uF / 120V capacitor + 27kom discharge resistor were connected the transient task of charging 100uf capacitor was to heavy heavy for SMPS to start.
Because the problem concerns SMPS the type of equipment the problem appeared is insignificant, but as pure formality here are the details:
TV set “Curtis” OTVC 2501, capacitor reference : C665 .