The set will be dead, no standby light, no response to power.
Section - 1
The power supply section of the set is dead.
We have to begin with its ON/OFF switch first. Check the ON/OFF switch for its pole continuity. On rare cases, any one pole of the power switch will be defective. The switch is a DPST [Double Pole Single Throw] type. If any one among these poles has an internal contact defect, no power will get into the power regulator of the set and thus dead condition.
If switch is found OK, come towards fuse [F600 – 3.15 Amps]. All component numbers here se refer can be seen on its printed circuit board, printed on both component and foil side. If fuse is found blown up, take a pause. Never put any more fuse, as there will be specific reason for this fuse to blow up. We must find it out first. If we insert a fuse without rectifying the problem to which the present fuse has been blown up, it may make more damage to components. Fuse is used here as a protection device to any short-circuit that may occur to internal circuits. Just find the reason for its failure, is the first thing to do. Just follow the circuit.
A special care should take before power up this chassis. We must have to detach the degauss coil connection plug out to place the main board in service position. Here the set uses one posistor [THP 600] with three terminals. A resistor [470Ohms/3W] is connected with its terminal [1] to AC supply line. Desolder this resistor out, or just lift up a little to get it disconnected from the circuit. Otherwise, a tremendous current will follow through this resistor without degauss coil connected, when we switch ON the TV after fuse replacement. It is best to desolder out the degaussing posistor out from it, till all the other work has been done and resolder it after. Moreover, if this posistor has shorted internally, the fuse will blow out as soon as we switch ON the TV. If fuse does not blow out when this posistor has been removed from the printed circuit board, we can make sure that the short inside this posistor caused the fuse to blow out. If this is the case, without this posistor, the set should work well. Then we have to replace this posistor only. The work is over.
The next step is to check the mains bridge rectifier [D601] and mains filter capacitor [C603]. But before checking these come towards the ‘switching regulator’ IC [D600 – STR F6707A], a most susceptible component in power supply section. Locate its pins (1&2). Check the resistance between these two terminals. It should never show a short (less than 1k). If found very low resistance, desolder out this component from the circuit board. No check the resistance across +ve and –ve terminals of the mains filter capacitor. It should be high. Before touching these terminals with probes of millimeter, properly discharge the capacitor; otherwise, multimeter will get damaged.
Continued on section-2
