CRT TV repair course by humphrey preview

List of ContentChapter 1:Introduction to Television Repair Career Chapter 2:Component found in the Power supplyS.M.P.S Chapter 3:Understanding S.M.P.S sub units Chapter 4: Solving power

CRT Television Repair Course

By Humphrey Kimathi

http://humphreykimathi.blogspot.com

The reader of this book is expressly warned to consider and adopt all safety precaution that might be indicated by the activities Herein and to avoid all potential hazards.

The author particularly disclaims any liability, loss or risk taken by individuals who directly or indirectly act on the informationContained herein The author believes that the information presented here is sound, but readers cannot hold him responsible For either the actions they take or the result of those actions

All Rights Reserved

No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without permission in writing from the owner

Preface

CRT Television repair course 2011 Edition is an E book covering all the major building blocks in CRT television with emphasis given

to real life scenario from the technician work bench and therefore provide a good source of reference for practicing technicians

The book is divided into two parts:

associated with these blocks

The book is illustrated with numerous color photos to make the reader learn faster and get the concept pretty fast

By Humphrey Kimathi

Part one: is composed of 18 chapters of the major circuit blocks in CRT TV and explains basic functions and common problems

Part Two: is composed of 10 chapters of pure real life repair histories from the technician work bench.

To navigate the book just click on the Chapter reference on the list of contents and it will jump straight to the very topic and

to go back to the first page just click on your keyboard (Ctrl + Home) key

This Book is Dedicated to

My Wife Rosemary

My Children Brian, Marvin, John and Grace

List of Content

Chapter 1:Introduction to Television Repair Career

Chapter 2:Component found in the Power supply(S.M.P.S)

Chapter 3:Understanding S.M.P.S sub units

Chapter 4: Solving power supply problems(smps) using control ic

Chapter 5:Solving power supply problem for Television using transistor instead of control ic

Chapter 6: Understanding the Secondary power supplies

Chapter 7: Main power fuse keep on blowing

Chapter 8: Do it yourself series lamp current limiter

Chapter 9: Using the series bulb for find shorted component on the primary supply

Chapter 10: Understanding the Horizontal circuits

Chapter 11: understanding fly back transformer

Chapter 12: H.O.T getting shorted after replacement

Chapter 13: Understanding and troubleshooting Colour problems

Chapter 14: Understanding and troubleshooting Vertical circuit

Chapter 15: Understanding and troubleshooting the Audio circuit

Chapter 16: Understanding and troubleshooting the Tuner circuit

Chapter 17: Understanding and troubleshooting the micro processor

Chapter 18: Understanding and troubleshooting the remote control

Chapter 19:LG Television NO PICTURE- AUDIO OK blue background

Chapter 20: PANASONIC TV MODEL TC-14E1T with intermittent single horizontal line (blue)Chapter 21:Gold star TV vertical partially closed

Chapter 1:Introduction to Television Repair Career

This course is intended for people who are already in the field of Television repair and have basicknowledge in electronics and therefore understand safety precaution when working on electronicsdevices

If you are already in the field of repairs you would agree with me that most of the electronics booksand colleges teach about the theory of operation and how components works

The moment you step out of that class and join the field is when you realize that things are gettingtough, the customer is not interested with your papers but….is my equipment working?

So the only way to make your customers believe you are up to the challenge is by quick diagnosing

of the problem and repair…Period!

This book is written to address the above issues comprehensively as most of the materials in

this course will be practical real life experiences from the technician workbench

Tools of trade

Every trade have his own tools of trade, for Television repairs the minimum you should have

include: Chapter 2:Component found in the Power supply(S.M.P.S)

various voltages to feed other circuit.

Power supply section of all electronics equipment is one area where there is a lot of stress for the equipment as far as components are concerned due to high currents and voltage involved and therefore most of the electronics problems will be power supply related and also the horizontal circuit which we will study latter in this course

For now let us concentrate on the switch mode power supply components and what they do and the effect they have on the supply when they fail.

So next time you see a fuse has blown you need to appreciate it for job well done, on the same note

I believe you have understood why you should never replace a fuse with a Jumper wire- always think safety first to you and also to your customers.

Fuse often fail by being open and you can easily confirm that with a meter set to low ohm

resistance.

Symbol in circuit board

This is also a safety component and is always connected on across the AC power line, but they do not conduct unless the AC voltages increases above normal like during power surge caused by Lightening or using outlet which is not well regulated like using generators.

line it will create a short circuit across the power line and hence force the fuse to blow and hence disconnect the equipment from further damages.

Most of the electronics equipment nowadays use switch mode power supply(smps) to generate

Chapter 3:Understanding S.M.P.S sub units

Hot ground/Cold ground

Component side

Bottom side

This is because powers supplies run under considerable stress due to high voltages and currents involved around these circuits.

in CRT television, you can use this principle in repairing CRT monitor too

note: Short in the primary side of the power supply usually cause the surge limiter or the fuse to blow

From now on we shall be using the main capacitor negative as the Ground for all the measurement ofVoltages on the primary side of the power supply

I have modified my meter ground probe with a crocodile clip so that I can attach it to ground point of theequipment I am repairing and therefore I use only one hand to probe the circuit

This is a safety precaution because as you know for there to have a potential difference there must be

a connection between the live and the ground

So if you are using your two hands and incidentally touch the live and the ground then current will flowthrough your body and this can be fatal But if you are using one hand it is not possible

Chapter 4: Solving power supply problems(smps) using control ic.

Most problems with equipment using smps like television and monitors are power related

In order to understand how to solve smps problem I am going to show you how to analyze common failure mode

If these two components are ok then most likely there is no short on the primary side of the power supply

These types of the television are also very common in the market and therefore I would like to

highlight how to go about them when troubleshooting their power supply

These television are mostly imported from china and if you have been working on them you will

notice that they all have the same circuit diagram but different faces and Names and therefore

On the above picture you can see the main component that you would find on the primary power

supply when you open up the Television Please take some time to locate these component on the

actual board if you have one near you

The First thing you should do when a customer bring in this type of television as usual is to confirmwhat the complain was…I mean if he or she said no power or no audio please confirm the same beforeeven opening the set

Then open the set and scan around the primary power component both the top and underside and seeown eyes without using the meter)

Then if there was no power at all check with your meter the state of the fuse or the surge limiter andsee if they are broken

If any of them is broken don’t replace it first before you check the state of the Chopper transistor(in

our case D1710)

Chapter 5:Solving power supply problem for Television using transistor instead of control ic.

in this lesson I am going to use an Akira Television as our case study

if there is catastrophic failure on any component(e.g a broken component which you can see with your

Chapter 6: Understanding the Secondary power supplies

outputs on the secondary side to supply different blocks in the television set

Usually the number of output from the secondary side of the chopper transformer varies from model to modelbut basically the minimum is two outputs

this television secondary supplies we will have covered all the china made televisions because from my experience these set are using the same circuit diagram, the only different is the external cover and

the model name but the moment you open one you will find that the circuit board is the same with veryGLD,AUCMA, FLAMINGO, etc

you notice that it has several secondary output and we will analyze them one by one

Before you analyze them first let me point out that all measurement on the secondary side of the power supply

we shall be using the cold ground has we learn t in earlier chapter

Also to check the output voltage from the chopper transformer you have to measure Voltage at the cathode

Of the secondary diode

If the switch mode power supply (s.m.p.s) is okay and working the way it should then it will produce several

To start with let analyze the secondary supply of the Akira TV made in china Please note that by analyzing

little variation and the moment you master one model there you go these television include include

Below you can see the diagram of the Akira television made in china and if you look at the circuit below

Chapter 7: Main power fuse keep on blowing

When you receive a television in your repair shop, it is usually very important to check the health of thepower supply

You can quickly check for obvious safety components to see if they have been triggered on due to faultelsewhere or not

The main safety components in the television power supply is the fuse and the surge limiter

I mean triggered by fault elsewhere because rarely does a fuse or surge limiter blows alone, there must

a cause why it has blown

Whenever you find any of these component is open and you replace it most of the time you will findthat the same component open again

This is because there is a fault(short) somewhere else and what the fuse is doing is a safety measure

to cut of the supply otherwise fire can even break out from the equipment

So the rule of the thumb is that whenever you find a fuse or surge limiter is gone never replace it until

To check the switching transistor set analogue meter to X1 and measure between leg marked C and E1)with the red probe on the middle leg C and black probe on leg marked E

2)with the black probe on the middle leg C and the red probe on the leg marked E

you have checked the condition of the switching transistor or control ic in that power supply

Chapter 8: Do it yourself series lamp current limiter

In this lesson we are going to learn how to make yourself a series bulb current limiter

Chapter 9: Using the series bulb for find shorted component on the primary supply

In chapter seven we discussed some of the causes that can cause the fuse or the surge limiter to blow

In this lesson we are going to learn how you can use the series bulb to find hard to find short in the

primary power supply I mean primary because short on the secondary side rarely causes the fuse

to blow but only causes the power supply to appear dead

Sometimes component can develop semi short and very hard to test them with a meter like one time

I came across a transistor which was shorted base-emitter junction which was around 82 ohms and

as you know most meter recognize a short if it reads less than 30 ohms

Therefore a component which is shorted and the reading is higher than 30 ohms the meter will assumethat it is okay but when you subject that component to the power source then it will manifest as shortThis is where this gadget comes in to help locate the component which is presenting short under loadUsing the above diagram/circuit you can disconnect the component highlighted with an arrow one

at a time and the moment you disconnect the culprit you will notice that the brightness will go down

Chapter 10: Understanding the Horizontal circuits

and therefore you will find more problems on this block more than any other on the secondary circuit

television and monitor is the B+ supply.

This is the supply which supply the fly back transformer to get other voltage which are generated by the fly back transformer just like the voltage which we saw in our previous lesson being generated by the switch mode power supply.

Horizontal circuit can be divided into two sections.

1 Horizontal drive circuit

2 Horizontal output circuit

From the diagram above the circuit on your left of the blue vertical line is the horizontal drive circuit Basically this circuit is composed of five important component which includes.

the drive transformer primary.

and horizontal output circuit

Horizontal circuit is another area which operates under a lot of stress in crt television and monitors

The main source of the secondary circuit in terms of high current which supplies the main load in crt

1.RC- network-used to protect the drive transistor from induces voltages from the drive transformer

2.Current resistor-Set the current and voltage to the driver stage

3.Filter Capacitor-Filter and boost the current to the driver stage by charging and discharging through

4.Drive transistor-act as on/off switch, can be either a bipolar or MOSFET transistor

5.Drive transformer-this is basically used for impedance matching between the horizontal drive circuit

Fly back transformer is probably the biggest component on the television motherboard and in this lesson

we are going to familiarize yourself with this component

The fly back transformer is feed with the main supply from the power supply called the B+ which is a

On the body of the fly back transformer it has two adjustable Potentiometers, the upper one adjust the focusvoltage and the lower one adjust the screen Voltage

The screen voltage behaves as brightness control and therefore whenever you find the screen is darkespecially after replacing the fly back and the screen is still dark even after using the remote brightnesscontrol button then consider adjusting this knob little and see if the brightness increases

Chapter 11: understanding fly back transformer

direct current(dc) and in return generates other voltages like the eht which is over 24 kV volts Dc for theEHT cap , the focus Voltage between 5 kV to 8 kV and the screen voltage which is around 200 to 800 vdc

Chapter 12: H.O.T getting shorted after replacement

This is a common phenomena with HOT whereby a customer bring in a Television and after checking

it find out the Horizontal output transistor(H.O.T) is shorted.

Naturally you replace the shorted transistor with a new one and you power on the Television and it come up beautifully and before you begin to celebrate the television goes down again(stop working) You open the set and after checking the health of the same component (H.O.T) you find alas it is