PART-5
Now we came the most important section of the power supply. The switching output section. Here an IC is used for all functions [oscillator and output] to drive an SMPS transformer’s primary winding. The secondary winding of this SMPS transformer generates all three voltages supplied to other printed circuit boards. They are 13VDC which appear at pin number 1 at CNM 901, 26VDC appear at pins 1,2,3,4 &5 at CNM 802, and 12VDC appear at pin number 9,10 & 11 of CNM 801. Pin number 15 of CNM 801 will be a constant 5VDC, and it is the standby voltage. If this standby voltage is all right, you can see the standby light at the front panel of the TV lights up, as soon as the set is switched ON. Check the 5VDC first if there is no standby light on the front panel of the TV. If there is standby light on the front panel, no need to check this voltage. It will be there. Check the other voltages.
Before replacing the switching regulator IC [ICM801S: F9222L], check all the other components related to its other pins. The most of the resistors and capacitors marked on this board will be SMD types [Surface Mount Types], and replacing them will be a challenging job. If this IC was found shorted, replace QM803 & QM802, even though they are found good. Replace the opto-coupler Ic [PS803S:WK707] too. The most important thing to note is to check all the solder points in this section for loose soldering joints or dry soldering joints. Resolder all the suspected solder terminals, by applying a little more solder. Check the solder terminals of the SMPS transformer [tm801] for loose contact. Reconnect the unsoldered [RM801] back into circuit.
If everything is Ok. The set should switch ON without any problem.
In most cases, the solder terminals of two regulator Ics used at the secondary side of the SMPS transformer was found loose solder points. So check and resolder the older terminals of these regulator Ics [ICM853:KIA278R12P1 & ICM852:MC33167T].
When replacing components to power supply regulator section, insist on original type and number used. Never make any experiment by replacing equalent or other types than specified. It may make things more badly.
On the 24VDC supply rail, which appears at pin number 1,2,3,4&5 of CNM802 & CNM803, should be checked for accuracy, as this is the main voltage that goes to the main board as well as the backlight inverter board.
If nothing can help you, or you feel difficulty in getting the exact component for replacement, it will be best to replace the power inverter board as card basis.