Friday, September 9, 2011

TV wont turn on?

TV wont turn on all i have is blinking of the litle lamp when i push the button.

In most cases the standby light might blink with different rapidity to indicate a fault relevant to the processor. It is possible that most of these indicate that there are errors in the processing section .Since there is a possible short or leak in the circuit the output driver section can take in huge current to trip the SMPS or from advice from the micro processor. Remove the power plugs and make sure that high voltage sections are discharged of the potential stored in capacitors. Look for visible signs of leak or of busted capacitors. Look for bulged capacitors or damaged components- burnt or busted. Use a multimeter to check the continuity or shorting in components, if so detach from circuit and test . If the voltage builds up and the set power ON and then shuts up then the suspected section must be checked in detail.

The processor must have the +5 voltage to the function properly , the +B and secondary voltages also must be checked to infer the fault. Trace with caution and in running through the signal path , circuit trail.

Read tips to check the SMPS unit:

To help in identifying common problems in SMPS circuits.

There was a time when we had only transformers fitted on all the appliances which was sturdy and could stand up to rigourous voltage conditions. The disadvantges was the growing cost of copper & lamination metal, the weight and the universal voltage condition.
The switch mode power supply came in to replace all the devices with an added advantage od space, cost and range of voltage but brought in higher failures when there was a voltage error.
So I am listing few tips to look into a SMPS failure and possible safeguards.
First of all in a SMPS failure if a fuse has blown the chances are there is a fault in the circuit and very rarely the fuse can be replaced unless the component is sorted out.
So check from the power supply the possible major components to suspect.:
1. Fuse
2. The surge protector -- usually a varistor ( metal oxide)
3. Rectifiers- in bridge circuit.
4. Chopping oscillators- Intergrated circuit.
5.Chopping drivers-- MOSFETS ( now incorporating a single IC for OSC and drive )
6. SM ferrite transformer.
7. Main filter capacitor ( will be seen as leak or short)
8.Discrete reverse feedback diodes, capacitors or fusible resistors .
9.Optocoupler which is the feedback trigger.
10.Short in the secondary circuit can switch off power by current limiting.

These are the most possible components that one must check on in case of a SMPS failure.
To prevent a SMPS failure it is important that there are no transcient surges in the line supply, So have a good tight connection. If isolation transformers are used for costly sets it will be ideal to check many failures.
Try not to leave the sets always connected to mains except if it is necessary to set the clock functions or timer functions.

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