CRT TV repair course by humphrey preview

CRT Television Repair Course By Humphrey Kimathi http://humphreykimathi.blogspot.com CRT TV repair course by Humphrey-Preview, Page By Humphrey Kimathi 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 information Contained 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: Part one: is composed of 18 chapters of the major circuit blocks in CRT TV and explains basic functions and common problems associated with these blocks Part Two: is composed of 10 chapters of pure real life repair histories from the technician work bench The book is illustrated with numerous color photos to make the reader learn faster and get the concept pretty fast 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 CRT TV repair course by Humphrey-Preview, Page This Book is Dedicated to My Wife Rosemary My Children Brian, Marvin, John and Grace CRT TV repair course by Humphrey-Preview, Page 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 22: Samsung Television dead Chapter 23: JVC 14'' DEAD AFTER A VOLTAGE SURGE FROM A GENERATOR Chapter 24: GLD TV FIELD COLLAPSE WITH A SINGLE HORIZOTAL LINE Chapter 25: JVC Television Dead 21” Chapter 26 :Chanwong TV-china with No Power symptoms Chapter 27: Sony TV 1902 GE NO PICTURE NO SOUND only screen display i.e channel Number Chapter 28 : Conclusion CRT TV repair course by Humphrey-Preview, Page Chapter 1:Introduction to Television Repair Career This course is intended for people who are already in the field of Television repair and have basic knowledge in electronics and therefore understand safety precaution when working on electronics devices If you are already in the field of repairs you would agree with me that most of the electronics books and 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 getting tough, 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: Page 5, CRT TV repair course by Humphrey-Preview Page 6, CRT TV repair course by Humphrey-Preview Chapter 2:Component found in the Power supply(S.M.P.S) Most of the electronics equipment nowadays use switch mode power supply(smps) to generate 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 and the effect they have on the supply when they fail Fuse When you switch on the Television via power switch, the power passes through a fuse which is used for safety purposes, so whenever you see a fuse has failed don't blame it because that why it there to do-that is to blow if there is a problem with the power supply like a shot, the fuse will cut off the power to the equipment to avoid further damage to the equipment And also preventing the equipment from catching fire! 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 Varistor Another components found in the smps in some of the good design is the Varistor, see picture below Symbol in circuit board Varistor This is also a safety component and is always connected on across the AC power line, but they 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 So if there a power surge the varistor will conduct and because it is connected across the AC power 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 CRT TV repair course by Humphrey-Preview, Page Chapter 3:Understanding S.M.P.S sub units Hot ground/Cold ground Component side Bottom side CRT TV repair course by Humphrey-Preview , Page Chapter 4: Solving power supply problems(smps) using control ic Most problems with equipment using smps like television and monitors are power related This is because powers supplies run under considerable stress due to high voltages and currents involved around these circuits In order to understand how to solve smps problem I am going to show you how to analyze common failure mode in CRT television, you can use this principle in repairing CRT monitor too Television is Dead Here dead I mean the set does not show any sign of life, power ON LED is not lighted and nothing happens even after power is switched on First confirm the television cable is not broken inside, you can check this by measuring the voltage across the AC power input connector on the circuit board If the voltage is reaching the circuit board, then look for the fuse and see if it is blown, if the fuse is okay check also the surge limiter is open or not If these two components are ok then most likely there is no short on the primary side of the power supply 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 of Voltages 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 the equipment 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 flow through your body and this can be fatal But if you are using one hand it is not possible CRT TV repair course by Humphrey-Preview, Page Chapter 5:Solving power supply problem for Television using transistor instead of control ic 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 in this lesson I am going to use an Akira Television as our case study 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 when a customer bring in this type of television as usual is to confirm what the complain was…I mean if he or she said no power or no audio please confirm the same before even opening the set Then open the set and scan around the primary power component both the top and underside and see if there is catastrophic failure on any component(e.g a broken component which you can see with your own 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 and see 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) CRT TV repair course by Humphrey-Preview, Page 10 Chapter 14: Understanding and troubleshooting Vertical circuit Another block where there is potential of problems in CRT television and monitor is the vertical circuit Vertical circuit problems can be manifested in many ways and therefore one has to be keen when getting clues associated with the vertical circuit because some of them not point directly to the vertical circuit has a problem but if one is keen you can always tell if its the vertical problem causing the symptoms or not From my experience whenever you see the television screen height is narrow(does not occupy the whole area from the top to the bottom of the screen) Then suspect some problem on the vertical circuit, others may have some write line at the top or bottom part of the screen Others you can see an horizontal line across the screen but there is picture at the top and below that line but the picture is somehow distorted/squashed but the sound is okay in all those scenarios Also black stripe above and below the screen is common, symptoms like lines on top of the screen or no image at the bottom points to a faulty Capacitor around the vertical ic CRT TV repair course by Humphrey-Preview, Page 19 Chapter 15: Understanding and troubleshooting the Audio circuit Some times on your line of repair you will encounter a case where a television is brought in for repair with NO audio PICTURE OK symptoms Please note that I mean the picture is present and very clear but there is no sound from the speaker If it is no audio and no picture this is a different case and should be handed on another topic Below you can see an audio circuit of a television using ic LA4266 things to look for here includes a) b) First be sure the television is not muted via remote control Set your meter to low ohm and test between the two pins of the speaker If okay it should have low reading between ohms and 16 ohms CRT TV repair course by Humphrey-Preview, Page 20 Chapter 16: Understanding and troubleshooting the Tuner circuit If you receive a set with the symptoms no AUDIO and No PICTURE then the best place to is troubleshoot is the Tuner circuit Usually for the tuner to function it will require the Vcc-in the above model is volts and if this voltage is missing then the tuner will not work and hence no picture and no audio CRT TV repair course by Humphrey-Preview, Page 21 Chapter 17: Understanding and troubleshooting the micro processor Just like computers television set have micro processor which control the functions of the Television Microprocessor are quite reliable and highly protected from static discharge and power surges Most of the time if you suspect the problem is as a result of bad micro you should first be sure that the following is okay because if any of the following is missing then the micro will not work Micro power supply- usually volts Micro reset supply- usually volts Crystal oscillator is okay CRT TV repair course by Humphrey-Preview, Page 22 Chapter 18: Understanding and troubleshooting the remote control The remote control circuit in television works like the transmitter and receiver in radio circuit Inside the remote control there is a circuit which emit pulses(signal) and in the TV circuit board we have another circuit which receiver signal and these pulses are send to the microprocessor for interpretations and action usually if you receiver a case where the remote is not working it is important to isolate if indeed it’s the remote having the problem or the receiver inside the television To isolate the problem you need to confirm if the television front buttons are working and the remote is not working If the front buttons are working then only can we suspect the remote control unit CRT TV repair course by Humphrey-Preview, Page 23 Chapter 19:LG Television NO PICTURE- AUDIO OK blue background This is a LG television made in Egypt (or is it made or assembled in Egypt) and the customer complain was No picture but audio is okay So I went down to his residence to check on it…remember most of my repairs are done on the site and therefore I normally some preparation for the task ahead of the time In this assignment I had prepared myself with the basic equipment plus a circuit diagram of the LG television (any) because mostly TV circuit diagram for a particular model are very similar in terms of major circuit modules In this case from the symptoms given by the owner via the phone I was very sure the problem was likely to be on the CRT circuit board, so I went down to his place and found he was not around but the houseboy was around to assists me with what I wanted Asking him about the television he told me that there was another technician there and I wanted to know how far he went into the television even before I opened it and he confided with me the technician came and after a keen observation on the screen for about ten minutes without his eyes blinking he told them that the problem is new in the world and therefore he sees no hope on the television and therefore the best place for it is in the dustbin or make it a toy for his children My friend that is why it is very important always to get a second opinion even in the medical world I mean if your doctor tell you that your leg need to be amputated (God forbid) please ask him/her for some times and get another doctor to hear his opinion For me I was very happy with this technician because he was honest with himself and never attempted to repair it because he could have done even more mess So I opened the set and went straight to the small CRT circuit (RGB) CRT TV repair course by Humphrey-Preview, Page 24 Chapter 20: PANASONIC TV MODEL TC-14E1T with intermittent single horizontal line (blue), sometimes screen is lit but no picture, sound ok Also the osd(i.e channel number is visible but blurred) Intermittent problems are mostly caused by dry joints; you can confirm this by hitting the Television gently with bare hand on the sides This I did and confirmed there were many dry joint because the screen kept on changing Sometimes I even managed to get a picture, which was reddish purple in color I mean this Television has all sort of weird symptoms The Television was using I.C LA7837 for the vertical Drive so I decided to Google for the datasheet of this IC and I bumped on this shown in the diagram below You know sometimes if you fail to get the circuit diagram of the exact model you are working on you can go round this problem by getting only the data sheet of the suspect I.C and this can go a long way in assisting you to know which pin is which for proper diagnosis Very important is the supply (v cc pin) which is very important because a new working I.C from the factory is as good as a bad one if the V CC supply is missing, it’s like trying to drive a new car without gasoline That is why it is very important to make sure the supply voltage to any I.C is present and is correct value So from the data sheet I was able to see that for this particular I.C LA7837 it is feed by three Voltage sources Pin is feed with 12 Volt DC; pin and 13 is feed with 24 volts each, Please note that the 12 volts is from the secondary of the power supply and the 24 Volts is from the secondary of the fly back transformer and therefore one can fail and the other remain but still the vertical I.C will not work I mean if any of the three supplies is missing the vertical I.C will not work and therefore if you find any of the supply missing be sure to the voltage testing from that pin backward and find out what is blocking the voltage Look for open fusible resistor or filter capacitor for that line has developed high ESR Usually if capacitor has high ESR causes the supply for that line to drop One thing I was sure about is that there was a problem with the vertical circuit I measured all the components around the vertical I.C and they seem okay according to my meter The voltages were also okay to me I.e main supply 24volts both sides of the diode, and 12 volts for pin CRT TV repair course by Humphrey-Preview, Page 25 Chapter 21:Gold star TV vertical partially closed This Gold star television came in with the customer complains the picture has a problem…so I powered the television to confirm his report As a technician it is very important to confirm what the customer has said in his presence otherwise the set might have gone to another technician with no color symptoms and when the customer picked it from technician A he/she didn’t bother to check the condition after staying at this technician A for six months with the usual excuse of lack of spares And was just returned to the box and brought to technician B who in this case happens to be you No color symptoms you have figured it is not a big deal and therefore you will hold it a bit to attend more serious repairs so two days later you decide to work on that set with no color So you apply power with your eyes fixed on the screen to confirm what the customer told you two days ago Pressed POWER ON button and nothing happens Checking on the power outlet it working well and therefore you decide to open the set to see if the fuse is gone and when you finally open the television you notice the fuse is okay but a lot of the circuit has been tampered with and components even missing including the microprocessor, you know how much it cost in your local currency Just when you have confirmed the above here comes the customer coming to see the progress of the set and as you begin to thank him for coming your way so that you can show him how his set was abused by the previous repairers he tells you that he only knows you and if you are not able to fix his set just bring it back the way it was with” NO COLOR SYMPTOMS’ Or he calls the police These things happen and if they have not happened to you yet please take my advice otherwise history does repeat itself So I applied the rule above and I switched on the Gold star television and I observed the following:1 The set came up beautifully and I noticed the picture was partially closed with a black slip below and on top of the screen Sound was okay As a technician you can make a lot of conclusion just by watching the screen if you have a good knowledge on how that equipment circuit works CRT TV repair course by Humphrey-Preview, Page 26 Chapter 22: Samsung Television dead I received a phone call from a customer who wanted me to go and check his television which has developed a problem and was not working So I walked to his residence for that mission with a few tools: a multi meter which in electronics world is actually the eyes of the technician, I mean you can’t see electricity (voltage) with your own eyes but the meter can see and tell you if there is voltage or not and a screwdriver to open up the set The set was brought to me and I asked a brief history of the set especially the last moment before it died, I was told there was some smoke seen coming out of the set before they switched of quickly I didn’t intend to confirm that by powering it on again and therefore I opened the set and started scanning around the power supply looking for a component with catastrophic failure because I figured that since there was smoke, there must have some fire also and where there is fire there must be a heat mark or component swollen or broken to pieces Yes! I noted one capacitor with the top part swollen, the capacitor was rated 100uF/160V, in electronics sometimes if you don’t have the schematic you can have an idea of the voltage expected on any line by using the working voltage of the main filter capacitor of that line, for example usually when designing circuit the rule of the thumb is that the working voltage of the filter capacitor should be double the expected voltage on that line Therefore a capacitor rated 160 volts like the one above expect around 90 volts to 120 volts on that line, usually in television this capacitor with the 160Volts rating supply the B+ voltage to the fly back and therefore it is the main source on the secondary side of the power supply output Next I decided to check the state of the fuse and it passed the meter test with flying colors, so I decided to apply power and some voltage testing I applied power and to my surprise nothing happened, no smoke so I concluded that whoever said that he switched off after seeing the smoke did it a little too late So I started my voltage testing, with my meter negative probe on the main capacitor negative pin, I started to test the voltage at the actual main capacitor and there were zero Volts …Nothing! Hint: when you get zero volt on a circuit means there must be an open circuit or component but not a short, usually a short causes voltage to go low and pulsating(at least there must be some funny reading on the meter) CRT TV repair course by Humphrey-Preview, Page 27 Chapter 23: JVC 14'' DEAD AFTER A VOLTAGE SURGE FROM A GENERATOR The customer complains was that the TV was blown by high voltage from a generator I opened the set and scanned around the primary side of the power supply and found the main filter capacitor was bulging out I replaced it together with the control chip (str-G6653) which almost always goes when there is power surge After replacing the two components the set came up but no color (Picture was black and while) with some very thin lines across the screen I hit the set softly with my bare hands and the color came on but intermittent CRT TV repair course by Humphrey-Preview, Page 28 Chapter 24: GLD TV FIELD COLLAPSE WITH A SINGLE HORIZOTAL LINE GLD TV FIELD COLLAPSE WITH A SINGLE HORIZOTAL LINE across the picture (clear picture below the line but distorted picture above the line Also white lines across the upper part of the screen There is also blank part above and below the screen In my opinion a technician and a medical doctor have a lot in common, we deal with symptoms(facts) analyze them and figure out from the data at hand the most likely cause of those symptoms Fortunately for doctors they have added advantage because at least with human being they can speak out how they are feeling, add some additional test and there you go, Drug prescription is done Ok? Now for technician’s machines don’t speak, therefore we rely heavily on keen observations, testing critical test point, some history from the owner on how the problem started etc to be able to figure out the actual circuit causing the problem (symptoms) at hand This part is very critical, the more information you gather the more likely you are going to narrow down to the actual circuit which is causing the problem If the machine (Television or Monitor) has something on the screen, you can get a lot of clues on the screen behavior even before opening the machine Let take this GLD TV as a case study, the information on the headline of the article is what I was able to observe on the screen I have tried to reproduce the symptoms on the picture below Screen height is narrow A SINGLE HORIZOTAL LINE across the picture Clear picture below the line but distorted picture above the line Also lines across the upper part of the screen There is also blank part above and below the screen These are strong facts all pointing to Vertical Circuit, am I right? NOW LET OPEN THE TELEVISION AND TEST OUR ANALYSIS After opening this particular set I noticed two capacitors 1000uf/35v which had their top silver part swollen I put my finger on them and they were also getting hot This was enough evidence that these two capacitors are faulty CRT TV repair course by Humphrey-Preview, Page 29 Chapter 25: JVC Television Dead 21” I was brought a dead JVC TV to repair; when I pressed the power ON button, I could hear the degaussing coil engage as usual on power on I opened the set and I measured the voltage across the main capacitor No voltage was found-absolutely zero volts Alas what is the problem now? All over a sudden I heard a loud crack sound and noticed a resistor has broken down—see resistor R904 above across the degaussing coil- what was it doing there in the first place(anyway in most set its written optional but in this case it was there) I never had a chance to know its actual value to date It was also very hot and broke into pieces CRT TV repair course by Humphrey-Preview, Page 30 Chapter 26 :Chanwong TV-china with No Power symptoms This TV has no power symptoms-first I checked the fuse and it was blown but not blacked inside meaning there was no heavy shot in the supply Remember a fuse can tell you a lot about the last moment of any equipment before it died (in medical terms postmortem) Fuse blown, dark inside - Means the machine died due to heavy shot Please be sure to use the light serious Lamp to bring up the machine after replacing the fuse Fuse blown, clear inside- Means the fuse might have died through natural dead After I replaced the fuse it didn’t blow again confirming to me that there was no serious shorted component (I mean component shorted which is taking the supply directly to the ground I measured the output voltages and there was none: absolutely zero volts Then I checked the voltage at the main capacitor and it was 320 v dc which is okay The voltage was also reaching the switching transistor collector same voltage I measured the S.O.T base voltage and it was 0.02 volts I followed the start up circuit divider and the voltage was ok and no resistor was open But from the above voltage measurement you find the Zero volts at the base of the s.o.t is suspect Either the S.O.T (v513)is sorted base-emitter because its taking the voltage to the ground ) Or V512(c3807) is shorted collector-emitter because it’s also taking the base of the s.o.t to the ground Or capacitor c517 across the collector emitter of v512(c3807) is shorted to the ground CRT TV repair course by Humphrey-Preview, Page 31 Chapter 27: Sony TV 1902 GE NO PICTURE NO SOUND only screen display i.e channel Number This is quite old machine over 10 years The customer complains was that the machine has intermittent picture on and off Usually if the picture misses they would tap slightly at the back of the TV at the RF inputs Also the TV used to have a drift on the channel when off (every time they put off the TV they must tune again because they find the channel is not clear) First suspect – dry joint I did a thorough check for dry joint and I did all that I could but to no avail Next is voltage checking around the CRT circuit and I noticed that the RGB collector voltage is high i.e 200 Volts before and after the 15 k resistor All the three cathode I measured the RGB BIAS VOLTAGE and I found 0.76 Volts in all three Hence the reason why the collector voltage was not dropping i.e its like the RGB TRANSISTOR ARE OPEN BECAUSE THERE IS NO BIAS VOLTAGE I followed that circuit up the main Jungle ic and the voltage was the same I suspected the ic could be faulty…but before I embark on that mission I was to be very sure it is that ic because it is quite expensive to change By the way all other low signal voltage were ok the v, 12 volts were ok meaning the ic and the turner is getting powered I did esr test around the processor ic and changed whatever capacitor I was not happy with but still no change Then when fixing the Ariel into its sockets I noticed that it has some effect like if there is some disconnection inside the turner CRT TV repair course by Humphrey-Preview, Page 32 Conclusion My dear friends and fellow technicians we have come to the end this course on CRT Television troubleshooting and repair And my final word I can give to you is a quote by Albert Einstein, the most famous physicist of all time, he was known for his brilliant mind and gentle spirit, who believed he was just one small part of the world, trying to figure things out He said…… Anyone with a functional brain can soon become an expert in any field if he or she would simply study the subject only fifteen minutes a day I believe if you can follow that simple principle when studying this course then I will be looking for you at the top Wishing you all the best in your future endeavors Humphrey Kimathi Author of CRT Television repair course CRT TV repair course by Humphrey-Preview, Page 33