Question about LG 42PX5D 42 in. Plasma HDTV

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Thanks, but it isnt that simple. Most of the supply rails are OK, but the feed to the ZSUS PCB shuts down under a problem in just one part of the overall P.S. Hard to work through on the PCB as you need to undo a lot of TO220 components to be able to work both sides of the pcb! Good suggestions! Thanks

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Well I just had coffee so thought I would share tips.

if you do something like I do when working out a system .
shoot a digital picture and print or edit it on-screen.

start by documenting removed and interconnected components.
mark inputs and outputs, then power flow, regulation, feedback
then mark the main divisions to each circuit
look for a data bus. HV area,
document the hot spots and damage
if it can be maintained in shutdown mode what area got cool.
a thermal picture of board would be very helpful but you can map it manually using hands , ir sensors or thermal probe (insulated)

I use an audio probe in a lot of circuits to listen to the signals.
though some scopes have audio and digital capture I found audio to be a lot faster once you get used to it. you can hear heat noise in the dc signals, you can hear caps ticking, data sounds digital. even different voltages have special sounds.

once you make this map of a board you will find troubleshooting much faster and easier as you record the data.

print out a couple of copies and work out a system to get to them quickly.
the hardest of all but necessary is to make a rig to run the unit outside the unit.

Get yourself a good analog meter, on the Rx1 scale it puts out a small bit of voltage so you can test transistors ,diodes and cap all in-circuit , reason. if you watch the rise of the needle and speed it falls, you can tell the overall time of the charge /discharge of circuit or cap.


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Posted on Jun 12, 2008


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1 Answer

What does a pcb look like i want to make sure i am right

PCB means printed circuit board.All the boards in your TV are PCBs, Please specify which board. example YSus, ZSus, Power Supply. Control board, YDrivers etc

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Will not power up. Tested from plug to power board. Power does not leave power board from any terminals.

The power supply board could very well be defective. I would also check the Zsus board and the Xsus boards. If either of these boards fail it could also cause the power supply board to fail.
You can unplug the connectors to the zsus board at the power supply and try to turn the set on. If it does turn on, the power supply board is ok. If not, the power supply is bad. If the power supply board is ok, undo the plug connectors that power the Xsus board and hook up the plug connectors to the Zsus board. Turn the set an and see if it stays on or shuts down. Part numbers should be on the boards. Zenith is really LG Corp. Their customer support number is 1800-243-0000.
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Yes sounds like it is "Detecting" a "Fault" condition and shutting down the Arc for safety, then it recovers, and it repeats, I think, you should Check, your Earth leads, Connections, and Overcurrent Protection Threshold if there is a control. Check power is going to the feed motor at time of arc, and if it is still getting enough or if it, the voltage to it,"Sags" under load...In this case it is a power supply problem.

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This is a fault in the power supply itself, I have just repaired one of these power supplies successfully.
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When reassembling the power supply, care must be taken to ensure that parts like the ferrite cored transformer are thermally bonded to the aluminium heatsink with a smear of heatsink compound.
When the power supply was first powered up following repair, everything was normal, the green power LED came on as usual, the supply outputs both came up OK, and the unit was not making any buzzing sounds, completely silent. The HDD now operated as normal when once again powered from this power supply.

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Did you check the simple things first?
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Loading the paper

Cut the paper off clean.
Slid it through the slot on the back.
The place the paper between the black plastic rail,
and the bottom of the calculator.
Keep feeding it in the slot untill you can see it under the
foam wheel.
The repedably hit the feed button until the paper comes
out the other side.
If it does not feed, the paper is not under the wheel far enough.
This should work on other similar models as well.

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1 Answer

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The Sony Plasma designe not to repair at component level your problem I believe in YSUS PCB you can adjust a few variables resistors on this PCB make sure to mark on the spot before turn you can alway go back to original point, set your plasma on normal channel turn the variable resistor slowly and observe the picture any spot will effect the picture if you can not adjust you need to replace a new PCB
Let me know how you go

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2 Answers

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1 Answer

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