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Do it yourself series lamp current limiter. Chapter 9: Using the series bulb for find shorted component on the primary supply. Chapter Understanding the Horizontal circuits. T getting shorted after replacement.
Understanding and troubleshooting Color problems. Understanding and troubleshooting Vertical circuit.
Understanding and troubleshooting the Audio circuit. Understanding and troubleshooting the Tuner circuit. Understanding and troubleshooting the micro processor. Understanding and troubleshooting the remote control. Real life repair histories. Gold star TV vertical partially closed. Samsung Television dead. Sony TV GE. NO Picture NO sound only screen display i.
The ebook price is only USD Copyright www. List of Content Chapter 1: Introduction to Television Repair Career Chapter 2: S Chapter 3: S sub units Chapter 4: 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 T getting shorted after replacement Chapter Understanding and troubleshooting Vertical circuit Chapter Understanding and troubleshooting the Audio circuit Chapter Understanding and troubleshooting the Tuner circuit Chapter Gold star TV vertical partially closed Chapter Samsung Television dead Chapter Horizontal circuit can be divided into two sections.
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 the drive transformer primary.
Drive transformer-this is basically used for impedance matching between the horizontal drive circuit and horizontal output circuit CRT TV repair course by Humphrey-Preview , Page 15 Chapter understanding fly back transformer 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 screen voltage behaves as brightness control and therefore whenever you find the screen is dark especially after replacing the fly back and the screen is still dark even after using the remote brightness control button then consider adjusting this knob little and see if the brightness increases. The focus knob is used to focus the picture and therefore if you find again after replacing the fly back the picture is dis focused then you also try to adjust the focus knob a little.
If you adjust the focus and still not change to the picture then perhaps the CRT is faulty or the fly back itself is bad, but before you change these first change the CRT neck socket and see if the focus improves. Also in some model the RGB amplifiers supply comes from the fly back transformer usually around Vdc This Voltage if it is missing or low usually causes the screen to be very bright and with lines across the screen but when this voltage is high causes the screen to appear dark blank.
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. 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.
T you find alas it is shorted again. This problem of H. T getting shorted immediately or after some times of replacement has given many technician sleep less night trying to figure out what is happening here!!
In the lesson I am going to give you some tips on what to do to prevent the H. T getting shorted after replacement. Usually color problems are easy to solve if you do some preparation to analyze failure on this circuit And the best way to analyze this faults is to do voltage testing on the critical test point of this circuit and by so doing you will narrow down to the actual fault section pretty fast.
But first you need to have a rough estimate of the actual voltages expected on those test points in order to analyze the information correctly. Below I have reproduced a chart of estimated voltages at those points but may vary from set to set but not too far from the figures below. Now that there is something on the screen it means the HV is present and therefore the fly back is okay and the heater circuit is okay and therefore not considered for troubleshooting.
First check for dry joints around this circuit by tapping this small board with the back of your screw driver and see if the color changes every time you tap this circuit softly. You can invest on a mirror medium size and be watching the screen from the mirror when you are working behind the television and you want to see the screen without straining yourself.
If the color keep on changing or you see some splashes on the screen expect dry joints around this board and therefore you should re solder it thoroughly.
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 do 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.
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. 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 LA Set your meter to low ohm and test between the two pins of the speaker.
If okay it should have low reading between 4 ohms and 16 ohms. Usually for the tuner to function it will require the Vcc-in the above model is 9 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 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.
CRT TV repair course by Humphrey-Preview, Page 22 Chapter 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. 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. So I went down to his residence to check on itremember most of my repairs are done on the site and therefore I normally do 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. 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. Also the osd i.
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. 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, its 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 LA it is feed by three Voltage sources. Pin 1 is feed with 12 Volt DC; pin 8 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 do 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. 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 you apply power with your eyes fixed on the screen to confirm what the customer told you two days ago.
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 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 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 cant 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 didnt 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.
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 do 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! 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-G 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. 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. Now for technicians machines dont 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 1. Screen height is narrow. Clear picture below the line but distorted picture above the line.