First off, this post is NOT suggested for the beginner, or the do-it-your-selfer who is trying to keep from paying for a TV repair, and is looking for technical assistance. You will not be able to provide the answers the people on here who will be helping you will need, as they are going to want specifics. *HOWEVER* for someone with some experience fixing LCD TVs, and those wanting to make some money at it, you might find some food for thought here. I would be interested in your thoughts and comments.
Notes for those who want to work faster:
I work in a facility that requires me to fix a lot of HDTVs. I rarely work on less than 10/day, 15 in a day is not uncommon. It is mostly board level replacement, but we are doing more and more component level repairs as the sets go out of warranty. In this kind of environment, you need to learn to work smart, and increase efficiency. One way I try to do this is in my troubleshooting strategy. I like to use techniques that tell me several things at once, as this can be a real time saver. In this process, I sometimes make "assumptions" that might raise a few eyebrows among troubleshooting purists, but they are assumptions that are based upon a LOT of experience over 33 years in electronics. Personally, I think they must be effective, as I work at the pace described above, and carry a rework rate of less than 1%.
The process starts with a 30 second inspection of the boards, looking for tha standard obvious symptoms - blown fuse (if glass type), bulged or leaky caps, burned components or circuit board areas, board cracks etc. This should all be standard procedure for an experienced tech.
As a side note, I have thousands of repair records that I like to analyze. The percentage of sets I see that have capacitors bad is less than 4%. The percentage of sets fixed by just replacing a fuse is even less. If a fuse is opened, it is usually due to a failure of some other component.
I want to describe my strategy for a dead set. Many people, when faced with a dead set, go to the obvious place - the power supply. I don't. The first place I go for a dead set is to the IR/Function Switch Board cable coming from the main board. It will be the cable that runs from the main board to the front panel controls and remote sensor. It normally has 6-10 pins, and is often located on the bottom or left edge of the main board. I can quickly measure the voltage on all of the pins. I am looking for 3-5 volts on usually 2 or more pins. 1 of those pins will be the power supply for those boards, another will be the IR sensor return. I then press a button on a remote pointed at the set, and look for fluctuation of the voltage on one of those pins.
By now, you are probably thinking I am delusional. But let's look at what we now know:
1) If we found no voltages, there is at least 95% certainty that your standby voltage is not present. We know this because the voltage for the IR sensor and panel switches MUST come from the standby voltage, as they must be present when the set is off. This supply is regulated down on the main board from the standby supply, but that regulator on the main board rarely fails, and you will quickly figure it out when testing the power supply in the next step.
2) If we found the voltages, we can be reasonably certain that the standby voltage is good, for the reason stated above. We also have learned that the IR sensor is working, and it's signal is getting back to the main board, assuming we saw the fluctuations described above.
Now, we were able to get all of this information in about 1 or 2 minutes once the set is opened. We have not had to refer to service literature. We have not had to locate the connector legend on the power circuit board, find the standby pin, count to it and measure it. I can check the voltage on all of these pins on the main board faster than I can look for the standby voltage at the power board.
The next thing I want to know is if my power board is working, or if I am looking at a main board issue. For this I use a little device I like to call my "main board simulator jig". It allows me to turn on most LCD TV power supplies, and backlight systems. It basically consists of 4 resistors, potted in epoxy, with a color coded wiring harness. The schematic, and photos of it are shown below. It is usually a quick process to disconnect the power connector to the main board (at the main board end), and insert the wires of the jig in the proper pins, as shown on the legend on the power board. I then plug the set in and look for the backlight. This can quickly show you if the power board is functioning, as well as the inverters and backlights. If the backlights are not lit, I then read all of the voltages on the power board connector and see what is and isn't working. If backlight is lit, we are more than likely looking at something other than the power board, probably the main. Once again, the idea is to maximize the amount of information we can glean from a given diagnostic test.
Notes for those who want to work faster:
I work in a facility that requires me to fix a lot of HDTVs. I rarely work on less than 10/day, 15 in a day is not uncommon. It is mostly board level replacement, but we are doing more and more component level repairs as the sets go out of warranty. In this kind of environment, you need to learn to work smart, and increase efficiency. One way I try to do this is in my troubleshooting strategy. I like to use techniques that tell me several things at once, as this can be a real time saver. In this process, I sometimes make "assumptions" that might raise a few eyebrows among troubleshooting purists, but they are assumptions that are based upon a LOT of experience over 33 years in electronics. Personally, I think they must be effective, as I work at the pace described above, and carry a rework rate of less than 1%.
The process starts with a 30 second inspection of the boards, looking for tha standard obvious symptoms - blown fuse (if glass type), bulged or leaky caps, burned components or circuit board areas, board cracks etc. This should all be standard procedure for an experienced tech.
As a side note, I have thousands of repair records that I like to analyze. The percentage of sets I see that have capacitors bad is less than 4%. The percentage of sets fixed by just replacing a fuse is even less. If a fuse is opened, it is usually due to a failure of some other component.
I want to describe my strategy for a dead set. Many people, when faced with a dead set, go to the obvious place - the power supply. I don't. The first place I go for a dead set is to the IR/Function Switch Board cable coming from the main board. It will be the cable that runs from the main board to the front panel controls and remote sensor. It normally has 6-10 pins, and is often located on the bottom or left edge of the main board. I can quickly measure the voltage on all of the pins. I am looking for 3-5 volts on usually 2 or more pins. 1 of those pins will be the power supply for those boards, another will be the IR sensor return. I then press a button on a remote pointed at the set, and look for fluctuation of the voltage on one of those pins.
By now, you are probably thinking I am delusional. But let's look at what we now know:
1) If we found no voltages, there is at least 95% certainty that your standby voltage is not present. We know this because the voltage for the IR sensor and panel switches MUST come from the standby voltage, as they must be present when the set is off. This supply is regulated down on the main board from the standby supply, but that regulator on the main board rarely fails, and you will quickly figure it out when testing the power supply in the next step.
2) If we found the voltages, we can be reasonably certain that the standby voltage is good, for the reason stated above. We also have learned that the IR sensor is working, and it's signal is getting back to the main board, assuming we saw the fluctuations described above.
Now, we were able to get all of this information in about 1 or 2 minutes once the set is opened. We have not had to refer to service literature. We have not had to locate the connector legend on the power circuit board, find the standby pin, count to it and measure it. I can check the voltage on all of these pins on the main board faster than I can look for the standby voltage at the power board.
The next thing I want to know is if my power board is working, or if I am looking at a main board issue. For this I use a little device I like to call my "main board simulator jig". It allows me to turn on most LCD TV power supplies, and backlight systems. It basically consists of 4 resistors, potted in epoxy, with a color coded wiring harness. The schematic, and photos of it are shown below. It is usually a quick process to disconnect the power connector to the main board (at the main board end), and insert the wires of the jig in the proper pins, as shown on the legend on the power board. I then plug the set in and look for the backlight. This can quickly show you if the power board is functioning, as well as the inverters and backlights. If the backlights are not lit, I then read all of the voltages on the power board connector and see what is and isn't working. If backlight is lit, we are more than likely looking at something other than the power board, probably the main. Once again, the idea is to maximize the amount of information we can glean from a given diagnostic test.
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