Topfield TF4000FI, Service Manual, Page: 17 / 62

17
5.5. The Advanced Test of SMPS.
--------------------------------------
Caution
-------------------------------------------
I. The SMPS must be disconnected from the mains plug to test.
II. The capacitor inside the SMPS (power supply) can hold charge even if
the IRD has been disconnected from the mains plug. To handle SMPS,
wait until the capacitor is discharged.
III. Very high voltage is generated in SMPS.
5.5.1. Check the damaged parts.
- Check point 1 –
Check whether there is broken part by visual test.
5.5.2. Test the diodes.
Check point 1 –
Check whether the diodes has crack. If there is a crack, replace it with new one.
Same part should be replaced.
- Check point 2 –
Check the resistance of all the diodes. If the resistance is too low (lower than 10ohm), it is the problem.
Replace it with new one. Same part should be replaced. Diodes is named as Dxx or ZDxx.(ex: D1,
ZD1)
To measure the resistance, you must remove the mains plug.
5.5.3. Check the Shunt regulator
- Check point 1 –
Check the voltage of U2.3(cathode). It should higher than 3V. If not, remove U2 and check it again.
- Check point 2 –
If U2.3 is higher than 3V, the voltage at U2.1(ref) should 2.5V. If not, replace U2 with new one.
5.5.4. Check the Pothocoupler IC
- Check point 1 –
Check the pothocoupler PC1. Check the resistance of diode part and potho Tr part.
If its resistance is about 0 or very low, replace it with new one.
Check if it has damages. And replace it with new one.
5.5.5. Check the Fuse.
- Check point 1 –
Check the fuse. Before replacing the fuse, check the other problem which can exist.
The same kind and rated fuse should be replaced.