ACER 193w - How to troubleshoot the power supply regulator board - SMPS
The fuse 901 blows as soon as the set is switched ON Click on the pictures to magnify
SMPS schematic
Check the MOV (VAR901) for short [If the input AC voltage is too high; this MOV will get shorted, and the fuse will blow up. This is a protection device against sudden over voltages. If the voltage goes too high than normal, this MOV will get shorted.
Check all the four rectifier diodes for short.
Check the capacitors C903, C902, C901, C938 for short. Desolder out each of them from the circuit, and check.
Check whether the FETQ901 (STP10NK70ZFP) for Source to Drain junction short. This is a common fault can occur to this type of circuit. If the Source – Drain junction gets shorted, means, the +DC voltage is shorted to floating Ground. Will result a fuse failure. If this FET shows a short circuit, there is a possibility for the damage of the SMPS control IC TEA1530AT. It will be best to replace this IC along with the replacement of the FET. If one among these resistors R904, R932, R933 is faulty, the power supply will not switch On. These three serially connected resistor supplies the start voltage to the SMPS control IC. If you found the FET is shorted, check all the solder connections of C906, R908, D900 for any loose solder. If there is any kind of loose contact to the connections of these components, the new FET replaced will get shorted as soon as you switch the power ON. You won’t get any time to measure and to find out the fault. So give special attention to these components, and their solder terminals. I strongly suggest replacing these three components along with new FET. The failure [winding short] of the filter transformer [L902] is very rare. Yet, check it too. The SMPS transformer short is very rare. I haven’t experienced any fault of it so far.
It is best to countercheck all once more, before Power ON the SMPS. After making a final confirmation, pull out the AC fuse from its socket, and connect a “Filament type 100Watts bulb” at two ends of the fuse holder; and Power ON the SMPS. If everything is OK, the bulb will glow bright at first [Due to the main reservoir filter capacitor – C905- charge], and will get dim within seconds. The bulb should go dim after 1 second, otherwise make sure that the fault hasn’t been rectified; and further check is necessary. If it is OK, then disconnect the bulb, and insert the cartridge fuse [250V - 4amp]; and switch the set ON.
