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50PC5D UL I changed the panel out. LG sent a sub. I had to take psu and main board off of old set. They sent the correct cables for new boards. But now tv comes on 5 secs and shuts off. I did autogen and get good test patterns. LG sent me a new main board. Still shuts off after 5 secs. All voltages are good. What am I missing? There is one cable connected to P705 on main board but I don't know where it goes. LG cant help me. It is a 4 pin connector. Does it go to control board? There are two ports both 4 pin. Help.

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  • Patrick McAlexander Sep 02, 2010

    This is a plasma

  • Patrick McAlexander Sep 07, 2010

    Thank you. You have been very, very helpful.



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I presume because you say "All the voltages are correct" that you must have a service manual?

Above is your troubleshooting manual, below is for a service manual, if you do not have one.

Support link below.

Right whenever a unit shuts down after a few seconds, the problem is usually an Overload, on the Power Supply or an output from a high current output.
You need to use an oscilloscope, and/or a Multimeter and monitor the main Voltage outputs, and see which one is failing, and subsequently shutting down the PSU. Usually you are looking for a short circuit, or nearly so, and usually the bad component(s) will be very hot. Often the bad part can be isolated using Freeze Spray, one freezes components one by one, and restart, the one that you freeze and clears the problem, even if only temporarily, will be the faulty component.
Now if it is NOT a faulty component, it may be that the PSU, is NOT getting the signal that indicates All is well, after the Computer does a self check, when finished it then signal to the PSU, that all is OK, and to continue to Power on, now if there is a logic fault, missing signals etc, then the PSU is instructed to power down, to stop any bigger problems occurring.
You say all the voltages are correct, well this maybe so up to a point, but obviously, they all Cannot be all OK, as it still shuts down.
You need to use the schematic diagram, and take readings around the input, output connections, and check, that indeed the Voltages & CURRENT drawn is within spec. This can be a long and arduous task.
As for your errant connections, well again the ONLY place this information would exist is in the Service Manual. You MUST check, using the manual, that signals and waveforms are exactly correct.
many many problems are actually within the PSU itself, so this is a good place to start. Then check, the load, (Sub Circuits) that connects to the PSU's individual voltage rails, looking for the problem that causes the shutdown. usually, if a short or partial short, the Voltage on that Rail, will dip, or drop, immediately before failure, I usually use my oscilloscope in Capture Mode, to check.
As related using the service manual, and schematic, work, along the Voltage rails, measuring waveforms and voltages and currents, until you find the faulty, section or component(s). Which should be replaced.
Also remember may Faults are Chain faults, meaning that, one faulty bit, may lead top another, like say, a faulty diode, is allowing AC ripple to pass and this in turn makes an Electrolytic Capacitor go faulty, so just replacing either one will NOT fix it, one needs to find and replace BOTH.
Good luck.

Posted on Sep 03, 2010

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The connections you are talking about only fit a certain way they are mistake proof.Your problem is in the hig voltage section of your TV though check the ceramic caps they are usually connected in parallel. Next to a transformer. Your set has three circuits like this for each colour gun. Take one lead of the caps out of the circuit. If one is reading below the normal farad reading of all the rest this is your problem. Make sure you check them all.

Posted on Sep 01, 2010


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