Friday, November 15, 2013

Basic electronic questions and answers all the way from India

Dear Humphrey 
Greetings to you from Dinkar Patel!

I purchased your Publication that is CRT TV Repair Course. Of course it is worth buying and very, very helpful for beginners like me. I am going step by step so it is very helpful to me.

I Have Sony CRT TV KV- R14Q1 I need our help as well as
Assistance to rectify the problems.

It is Powering On, Fuse, Switch, Main Capacitor seems to be
OK I checked up voltages as per your guidelines in the above book.
I have following doubts to clarify yet:

1. What is the procedure to test Opto coupler in circuit? If not then, after removing from circuit.

Opto coupler is basically composed of two components in one but not electrically connected.

1. Photo transistor-Photo means light, therefore photo-transistor is a component with is sensitive to light.

Usually has two pins collector and emitter, the third leg Base is not visible and is the one which receive the light signal from the L.E.D on the other side. So because the visible leg is the collector and the emitter pin, one can test it as the ordinary transistor whereby you should expect high and high using digital meter is diode mode either way.

 When doing in- circuit test this refers to the two pins of the opto coupler on the primary side of the supply.

2. LED- on the other hand L.E.D is light emitting diode; this means if you apply some voltage the LED will emit light.

For testing purposes an LED is tested just like an ordinary diode so if you set your meter to diode test mode expect to have one reading only(high/low) if the LED is good. The LED pins of the opto coupler are the ones on the secondary side of the power supply

2. Is it necessary to provide insulation to Power Regulator
IC STR S6307, If Yes the What kind of Insulation? How it will dissipate excess heat?.

No, usually the IC STR S6307 comes in a plastic package (over molding) and therefore does not need any insulation.

I guess it dissipate heat by conduction.

3. Testing Procedure of Horizontal Drive Transformer (HDT),
Can we test it in circuit with Blue Ring Tester?

These rarely have problems; I think blue ring tester will not be able to test these.

 4. Some of Diodes are tested in circuit with Digital MM,
Shows Both way Reading and some shows for few seconds both way and there after OL. (I shall test it with one leg removed, but it will at next point).

The sure way to test a diode is with one leg out of circuit (out of circuit)

 5. Some of the Resistors decreasing their Resistance in circuit but when with one leg removed it reads near to exact value. What could be the reason?
This depends on how resistor relate with other components, usually when resistors are connected in series give higher resistance and when in parallel they give lower resistances...

For testing purposes if the resistor has higher resistor in circuit that resistor is considered bad but if lower the resistor value it is okay…as you said once one leg is removed out of the circuit the resistance will go back to the normal value as you  have rightly put it…that was good observation..Congrats.

Please help me Humphrey to clear my above issues.
With kind regards,
Dinkar Patel from India.

Regards Humphrey

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