Thursday, June 7, 2012

Feedback and more questions from Afghanistan

Hi Humphrey,

Hope you are fine and doing well.
I have read the eBook, it was very interesting and i learned so many things from it.
But some question still I have and I would like you to explain them for me. The questions are as follows.
How the HOT switches ON/OFF very fast? 

Is the mechanism inside the HOT is like that, or it is switched OFF by the one of the output voltage of FBT though another Transistor or something, and when it is switched OFF there is no output voltage from FBT, and when there is output from FBT the HOT is switched ON again, and this way it is witched ON/OFF very fast.

Good question, this switching on/off is controlled by the horizontal oscillator...usually this is found inside the Big main ic in the television…see chap 10 and look for the example of pin 23 where you have the horizontal out pin…this pin send out pulses to the base of the drive transistor..Amplified then through the drive transformer for the purpose of impedance matching then finally to the base of the HOT transistor.
This transistor then switches on/off at the rate of 15625Hz (I mean15625 times per second)

If we give a constant voltage (without a transistor) in the primary winding of a transformer, is the voltage produced in the secondary winding? or without the transistor it is not possible to make a step up/down transformer or to step up/down the power.

Again good question. Transformers are not designed to work with DC. Remember the B+ is direct current and therefore if you pass it through the transformer nothing will happen…in fact it is not healthy.
I know you have in mind the linear transformer used directly on power outlet in radios and amplifiers, let say the one which step down 240vac to 12vac.

Remember the power outlet has 240Vac/110Vac and a frequency of 50Hz/60Hz (this means it’s not smooth and therefore keep on changing (oscillating) at the rate of 50 times per seconds) and therefore does not need an oscillator.

How we can find the audio circuit in the TV board?

Audio ic usually has heat sink and if you follow the wires from the speakers will also lead you there.

What are the functions of the ICs (micro, vertical, jungle, audio, RGB and Etc...) in general?  

Micro-Many functions but basically used for communications between you and the television..Take for example you press volume button on your remote control. this will send a signal to the micro and it will interpret what you have done and increase the TV volume and vice versa.
Vertical ic- used in vertical circuit…basically used to open the screen vertically.
Jungle-many circuits inbuilt here.
Audio ic-used in audio(sound) part of the tv output.
RGB-Red, Green, Blue- may be ic or discrete. Basically used to amplify the and blue signals for the color circuit.

What is the function of the crystal oscillator in the TV near micro and in the remote control?

Basically for generating pulses…

What is the function of IC jungle? Isn’t it the Horizontal out ic in chapter 10, that give pulse to the H-drive transistor?

IC jungle-jungle basically means many functions. Yes one of its functions is generating horizontal out pulses.

Inside the CRT is the anode cap (HV 24 -27 Kv) is connected to the shadow mask? Where the screen and focus voltage are connected in the electron gun? Are the connected to heaters or somewhere else?

No it is separate-the heater is the like a small bulb inside the neck of the CRT tube. Usually it uses AC.

Best regards, and thank you very much.Naseem

Dear Humphrey,
Thank you very much for your nice answers, they were really useful and i learned more things.

in future if i face a problem that i cannot solve it, i will ask you for help.

Best regards,Naseem

Hi Naseem,
Thank you for your positive feedback and glad to hear that my answers were useful to you. sure please don't hesitate to come back to me in case you have any issue in relation to this exciting career.

Regards Humphrey

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