I have a schematic of the power supply and have used it to check it's components. The only thing I found was a open 560K resistor in the string of four that bias the FET. With the set off and pluged in, the voltage on the COLD side is only about half what the schematic calls for. Is this normal?
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This is a general answer to your question:
Your TV is shutting down because it is consuming too much current from the internal power supply. The power supply has a protection cct
to protect your TV from further damage. If yo have any technical background, then you can follow these simple steps to troubleshoot your TV fault with the aid of a schematic diagram. Let us revise what you need for your job:
1- You need a schematic diagram for your TV model
2- You must be very careful when dealing with powered equippments
3- You need to prepare all the required tools to start your test and repair
4- You must be very confident that you are able to do the job using scientific steps. We all have done many mistakes but at the end we became experts in our fields. Please remember the fault is hidden somewhere and you are going to dig it out.
Let me start now:
-Disconnect any device connected to your TV
-Plug your TV to the Main
-Power on your TV, If the fault is still persisting then check the timer setting of your remote control or take the batteries out. Restart your TV again and if the same problem appear then we need to start our repair now. I personally advice you not to do any think if you don't know what you are doing, but if you want to learn, then do the followings without powering your TV.
- Disconnect your TV cable from the main
- Place and secure your TV on a clean wooden bench.
- Remove the back cover carefully
- look at the boards and identify which is which and compare it with the technical diagram of your TV.
- Identify the power supply section. Remember that 50 % of the TV faults are within the power supply and the rest lies in different area. Furthermore, many faults occurs due to bad soldering, sparks,loose connecters, metallic debris, excessive heat and bad ventilation.
Now if you have identified the power supply board(SMPS) which is very easy to find, disconnect the output jack and test each of the male and female jack pins with the ground. Use an AVO meter (put the selector to ohms) to check for any short cct with the ground. Remembr that there are some pins connect to the ground in both jacks. If you find any thing abnormal then compare your findings with the diagram. Alternatively, you can power your TV and measure the voltages at the output pins of the power supply and compare your readings with the service manual, but please be very careful. Again remember that switch mode power supplies (SMPS)
can work with a range of voltages 90VAC-240VAC, so if you have a step-down transformer from 220VAC to 110VAC, then it would be great and more safe when conducting your tests. In this test we can isolate the fault if it is in the power supply or in a different place. Also remember that your AVO (DC voltage) readings would appear higher than normal because we have isolated the load.
If the power supply was perfect then we are sure now that the problem is somewhere else, but in certain and limited cases some SMPS cannot provide the required power to the load due to internal changes and shifts in the values of the components in the loads and the power supply. In this case you need more experience to identify the source of the problem.
We have now finished from the power supply, however in the old TVs there is another power supply source which is the line transformer. This one is very simple and I am going to discuss that later.
Hi you will probably find it very difficult to get the parts for that make of telly did the repair shop look inside the telly or did they just turn you away when they see what make it was. The problem your having could be one of a couple of things. The first thing to check would be the internal fuse only check this if you have nothing at all coming on not even the standby light. If the standby lights on then the fault would be in the high voltage part of the board. I have looked everywhere for the schematics for your telly and have been unable to locate one on line. The place to start looking for the problem if you are able to look yourself but only do this if you ahev some experiance in this kind of thing else you could damage the telly further. If the fuse is blown you could change this first but if it is blown you need to find out what has caused it to blow. You will probably find that it could be the power relay transformer that the power lead goes into inside the telly this is the most likely problem because if this was fine then you would at least have the standby light on as you dont then it probably is this. It could even be a resistor or transistor around this part that has gone these will also need testing but without schematics you would be guessing so that would be the first thing to do is locate schematics i have looked and not found any yet but will keep looking for you will let you know. As for parts if you can get the part number off the part thats gone then you might be able to source one using search engine but you will need to get the part number, this would be on schematics also. If you arenot able to repair this yourself but can get the part number and source the parts yourself then repair shop should fit them for you. Ill have another look now for schematics and also see if i can source any parts for your make and model ill get back to you soon ok
Possible fault could be that any electronic component is either malfunctioning or you have a case of dry soldering , loose connection on heating of components. when the set trips off try to tap gently for resumption. if not cool off and switch on, If you are familiar with electronics open the rear cover, check from the power circuit onwards for visual dry connections, further you can take a voltage check when the set switches from the power supply to the output drives .hope this will help
If this appears after extended operation - an hour or more - it may just be a build up of dust, dirt, and grime over the years. After understanding the safety info, some careful vacuuming inside may help. Just don't be tempted to turn any screws or adjustments!
Dust is attracted to the high voltage section in particular - even the front faceplate of the CRT collects a lot and should be wiped with a damp cloth from time to time.
If the symptoms develop quickly - in a few minutes or less, then there could still be a dust problem - a power resistor may be heating a wad of it but other possibilities need to be considered.
If not dust, then probably in the power supply but realize that TVs don't have a nice metal case labeled 'power supply'. It is just a bunch of stuff scattered around the main board. Without identifying the part that is heating, a diagnosis is tough especially if the set really does work fine otherwise. However, if a series regulator were faulty and putting out too much voltage, the set could appear to work properly but in fact have excessive power dissipation in certain components. If cleaning the dust does not solve the problem, you will probably need a schematic to identify the correct voltages. You have to take the television to the manufacturer, Thanks...
If the TV is the conventional CRT type, normally, all you would need to adjust would be the brightness level and occasionally the picture (contrast).
In some instances when both settings are at the maximum but the picture is still dark indicates a hardware fault inside the TV. Often, this would be a simple resistor that has opened up in the G1 or G2 located at a squarish PCB at the rear of the CRT. This is relatively an easy repair job and low cost.
The worst possible scenario, this could possibly be a major component failure such as the tube itself or some other part(s).
Should you venture a DIY, you would need familiarity with electronic components and circuitry, use of a DVM and a soldering iron as well as access to a service manual or at the very least a schematic diagram. Should you be uncomfortable going this route, perhaps your best bet would be to seek the services of a qualified professional.
Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.
Sounds like there is a Power Supply problem. Maybe a common problem of the Electrolitics drying up. This can also cause the Power Supply to short circuit and resistors can go Open Circuit. Get a Technician to look at it.
Is a good thing the main fuse is not open,your problem is in the power supply ,as I understand you have no indication of power(no lights,No clicks)The 5 volts that power the microprocessor might be missing,this 5 volts usually come from a regulator,this regulator should have 12 volts in one side and the 5 volts in the other,the 12 volts come from the secondary of a transformer and it has its own fusible resistor,if the resistor is open is because the regulator is shorted and it need to be replaced.This is a good place to check.Be careful when checking this parts.If you are not too familiar with tv service seek the assistance of a servicer,it should not be too expensive.
you have a vert sweep colapse. Fisrt thing is to get a schematic diagram and find the vert. output Ic and the clamper diode. Measure the voltage on both sides. If its low then its apossibility that the Ic was drawing loads of current and blew out the b+ feed resistor. Look on the schematic and trace back the voltage line from the vert output ic back to the sweep power supply on the secondary of the flyback transformer. check the limiter resistor to the feed and if its open replace the cap right there the resistor as well as the vertical output Ic ALL AT ONCE!!! If you dont you will cause it to go out again in a short time. Good Luck.. If you post the vert part of the schematic I will be more then happy to assist you with this repair.