Let’s check fault to power supply board, step by step.
Consider the set is in dead condition. No standby light on its front panel lights up. No response main powers ON/OFF switch.
Check first the continuity or AC cord. You can check it with a multimeter, set to Ohms range. Check both conductor of the ac cord from plug point to the connection point to main power ON/Off switch for continuity. If found faulty, replacing it must rectify the problem to your set.
If mains cord is found OK, check the contacts of the mains ON/OFF switch. It is a DPST [Double Pole Single Throw] type switch. If any one among its contact inside has trouble, main AC power won’t get into the set, causing a dead condition.
You can check the contact condition of the switch with the help of a multimeter, as we did to check the continuity of AC power cord earlier.
If Ac power cord, and Mains Power ON/Off switch are found OK, we have to troubleshoot the circuit board for proper working.
Be very careful while working with power board of any TVs, as mains power will be present there, when we switch on the set, and mains filter capacitor will hold a charge for a long time, which can hurt us. Use of a hand glove is recommended when working with power boards.
Unscrew out the power board from the TV; Place it on a nonconductive surface
Inspect it. It will have four output connectors [CNM 801, CNM 803, CNM 802 & CNM 804]. All these four connectors carries output voltages from this power board feeds other board of this TV. There will be an AC input point, to which AC is fed from two poles of the ON/OFF switch. Come to this point
There is a fuse [Over current Protection]. It is a 6.3Amps fuse. Component number to this fuse will be marked as FS801S. All component numbers will be printed on the power board, both on component side and print side. From here, I’ll give you the components to be checked in a format [component part number on board: actual component number] hereafter.
Check [FS801S: 6.3AMPS FUSE]. If found blown up, make sure that some thing short circuit is there on the power board. It should be due to some shorted component or components on board. Check and find out this component/s is the main thing with repair. Find out the exact point of fault, and exact component, which has got damaged. Be very patient, careful and concentrate on work only.
If mains fuse [FS801S] is found blown out, never insert a fuse to the fuse holder first. Check the resistance across the [RX801X: 750K], which is connected across the AC input. The multimeter should read high value resistance nearly 700KOhms here. If it is found very low reading, say in Ohms value, Check [VX801X:INR10D751], for short. Resolder this component out from the circuit and check its resistance. It will look like a disc ceramic capacitor, it is not a capacitor. It is a Metal Oxide Veristor [MOV], used as surge protector. It is used with most of the present electronic device’s power supply section as a protection device. It has a peak threshold voltage value, say 400VAC or so. If any voltage spike appear with AC power line, over this threshold voltage, even for moment duration, the MOV will get shorted, resulting the mains protection fuse [FS801S] to bow out, thus protecting the device from further damages. In most occasions this will be the fault. If MOV said above is found good [reading across its two terminals is very high; up to Megohms], we must go to check further
To be continued: on part-3
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