Phase line coming into the main input AC is obtained to the bridge rectifier through the fuse F1 5 amps. neutral line obtained to the bridge rectifier to the thermistor TH1 MF 72 -SD9 NTP . Fuse is used for the protection against over current or short circuit. Thermistor is used for protection from jerks because of UP and down in the AC supply. converted into DC supply through the diodes D1 to D4 RL 207 of the bridge rectifier. negative supply being out from the bridge rectifier shown by the spiked lines and its known as the floating negative.
This section is converting AC 220 V supply in DC and filtering and storing. there are four diodes in this section for converting AC into DC , which are called as bridge rectifier, through full wave rectification by bridge rectifier, +330V and -330V are obtained from main AC 220V supply. negative supply obtained from the bridge is called the floating negative.
There are two electrolytic capacitors (330MF200V) in the filter section for filtering and storing the DC +330V AND -330V obtained from the bridge rectifier section. these electrolytic capacitors are connected in series, because of which working voltage of the capacitor is doubled, whereas the capacitance is divide into two parts of equal.
Two resistance are connected in parallel of the two capacitors for the purpose of discharging the two capacitor. voltage is divided in equal parts at the middle points of the capacitor used as the voltage divider, therefore,+ or - 160v supply is out from the middle point of the capacitor. this trigger supply is given to the one end of primary winding of SM transformer. on the other end , high signal output is given from the switching section to turn the SM transformer ON, DC supply which is the output of the rectifier section and filter section is given to the starter section and switching output section.
AC FUSE BLOWS OFF
check bridge rectifier diodes(bd1 -bd4) RL 205 may short. second one check DC 330V filter and stored capacitors (c5 and c6) 330 mf 200v any one of capacitor may short. third one check output switching mosfets any one of mosfet may short.
NO DC ACROOSS BRIDGE RECTIFIER
Check mains on/off switch, A/C power supply mains card, SMPS on/off switch, check for FUSE open, check thermistor TH MF72-SD9 OPEN.
LOW OUTPUT DC VOLTAGE
any one of bridge rectifier diode may open, check 330 mf 200v dc filter capacitor may open or leakage.
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