Hi,
There is some problem with the winding of any one of the chopper transformer in the inverter board. Thats why it senses the over load and shuts of the oscillator stage of the inverter. Remove the Chopper transformer one by one from the baod and inspect is there is any buring in its secondery winding.As it is a hight voltage transformer (above 1000v) chances to the winding get burned (shorted). Some time it will not be vissible, if the inner section of the winding is burned. If so remove all the transformers and check the ohms of winding or the indectence of the secondery winding of all the transformers. Ohms or inductance should be very near values for all the transformers. If any one shows more than 3% difference then its winding is short. If the transformer is avilable then replace the same, if not you have to replace the inverter board. Also you have to check the high volatge non-polar capacitor for short (if short will show low ohms. have to check after removing from the board ) in the secondary side of the inverter board .
ok
Hi,
Remember that you have to check the inductance (you need inductance meter) of each transformer's secondary winding . Even if the transformer is short it will provide desided output by the help of feed back circut. ( feed back circut is used to control and maintain the output voltage at a constat level. it is an AVR circuit automatic voltage regulator circuit. It will help to drop down the output voltage if the output voltage is high and will step up the ouput volttage if the output voltage is low by giving feed back voltage to the primery drive oscillator ic.). At this time it will drain a high current from the primary satge and will swich of by protecting the primary drive section and power supply. So dont think that tarnsformer is ok if there is light when using the test tube that you have.
ok
hi,
If you disable the protection circuit it will lead to total failure of inverter or the power supply. I can't lead you to do such a thing. Portection circuit is a must and it should be there.
ok
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There's a good chance you have failing electrolytic capacitors either in the power section or the inverter section or both. In your case, most likely the inverter section.
Any caps in these sections that look bulged at the top, even slightly, or bulged/leaking at the bottom (look for discoloration of the circuit board around the base of the capacitor) need to be replaced.
If you repeatedly turn it off and on, eventually it'll probably stay on, but every time you turn it off, the unit will get harder and harder to start up until one day it just won't.
Sometimes you have to do the opposite to start it up and unplug it for some time and then try again.
If you aren't tech savvy, don't worry, read the rest of this solution and watch the videos.
If you are handy with a soldering iron and can identify the power supply and/or inverter / FM section for the backlights, an inexpensive handful of capacitors will likely fix you right up.
Match the capacitance on the capacitors. Go over voltage if you can, and still have them fit.
IE - it's not a bad idea to replace a 10V cap with a 16V or 25V or even a 50V, but don't replace a 680uF cap with a 500uF or a 1000uF (unless you are SURE it's only doing supply output ripple filtering,
and even then, you should go OVER, not under the uF rating).
Most of the caps that go are 10V 1000uF or 3300uF.
I found some great videos of the procedure (for many Samsungs with the same issue) on youtube.
http://www.youtube.com/watch?v=Mm51C_RDIZE
http://www.youtube.com/watch?v=BNHHrgX_6cs&feature=related
http://www.youtube.com/watch?v=8l0AUj8QUkg&NR=1&feature=fvwp
http://www.youtube.com/watch?v=Y7b_nTaZYcU&feature=related
Backlight related video here:
http://www.youtube.com/watch?v=6XoF6QZ1dmw&feature=related
As you can see, this issue spans plasma TVs, as well as large and small LCD TVs and monitors, amplifiers, computer power supplies and motherboards, and other electronic equipment.
The parts are cheap, and skill required is minimal.
A great parts source is Digi-Key, and you can order the parts online at www.digikey.com
They typically cost under a dollar a piece plus a flat shipping rate.
The parts usually arrive one business day later.
If you watch the third video, you will see that even someone with no soldering experience can perform these repairs as demonstrated by the woman in the video.
You really need to look for bad caps...when these things cause inversion circuits to go off frequency, they under or over load the supply and cause a protection shut down....in these cases you can troubleshoot the protection all you want, but the end result is the protection circuit is doing exactly what it's supposed to. The other side is when the power supply is off frequency and the voltage drops under load causing again the protection circuit to trip and shut off the inverters - of course allowing the supply to go right back up to voltage - meaning if you are measuring the supply with a meter, it will appear perfect. You would have to be looking at the power output with an oscilloscope to see the blip that triggered the protection.
Again, bad capacitors being the problem.
Before you assume you know more about these things than we do, try listening to what we say..sometimes we actually have an idea of what we're talking about.
If you indeed replaced ALL the capacitors in the power supply AND the entire inverter circuit, then I am indeed at a loss. Protection circuits rarely fail, and the symptoms you are experiencing are 98% of the time simply a degrading capacitor (since it does work briefly).
All I can suggest is forcing the enable line high (disconnecting it from the protection circuit) and see if the backlights stay on. If they do, you might have a bad transistor or mosfet. A non recommended solution would be leaving the enable line high disconnected from the protection circuit if indeed the protection circuit itself is the fault.
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Whn you say no backlight, do you mean you still have sound? Also are you able to see a faint picture on the screen if you focus a flash light on it from close distance?
You did not tell me whether you have sound which confirms that the 12v required for the mainboard is also there in case of which we can confirm that the source of the problem as LCD Controller AKA T-con as the source of the problem. The t-con is inexpensive(costs about 40$) and easy to replace. So if you can just get me this info I can tell you how to proceed.
The protection circuitry is designed to shut off voltage to a component in case of failure. This mechanism exists to prevent damage to the set. You cannot/should not bypass it. Besides you say you have backlight so it's not the inverter that's faulty but rather the t-con. You have not responded to any of my questions and we cannot confirm the source of the problem. I am gonna ask you again. Do you have sound even though there is no picture? If yes then let me know and I will help you fix it by replacing the t-con so that the protect error won't be triggered.
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Hi,
If the supply voltage are present in the power supply board, the fault is between the backlight or the inverter board. Once there's no high voltage generated by the high voltage transformer within one second upon start-up, backlight feedback circuitry is turned off and trigger that kind of symptoms.
You have to check for busted backlights, it will produce an overload to high voltage transformer and will trigger the feedback circuitry. Busted bulb can't be test using the multimeter but has a physical indication of fault like blackened end. You can easily identify it by physical inspection. Much better also if you have a spare bulb to swap to a suspicious one.
Check the resistance of high voltage transformer's secondary winding (directly connected to the bulb by two wires, pink/white) using a multimeter. Compare the reading, all secondary winding of the high voltage transformers should be the same, if you found lower/higher resistance from one transformer, it is considered faulty.
Jdvillanueva
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If one of bulb is busted, I would see uneven background light.But background is perfect.
I tested resistance on transformers they all fine.
Pink/white wires run separate bulbs, not one bulb.
There one black return wire, which plug into inverter.
I test that one, it connection is good as well.
Inverter does generate HV, but only for 2-3 second than shots off.When its run, no discoloration onscreen, no pinkish.That tells me bulbs are good.But something shorting it off.If you apllay 5v on enable wire you will see screen light up for 2 seconds.This is very common problem , don't you have solution for it?/////
On this model, no HV transistors, but HV surfase mount ICs
Do you know how to disable short down???
To make inverter run.
No broken bulbs, no bad transformers, No bad HV ICs.Back light runs for 2 seconds, goes off.If disconnect & reconnect enable wire from mother board, have back light with Akai logo on screen.
nO BACKLIGHT, If you shine flashlight faint pixture , good sound.
My way of testing each bulb is simple:
I have good working bulb from PC monitor back light that I use as load for each HV transformer.
IT works every time.That why I know , Idon't have broken bulb or deffective HV transformer.
I have problem with protection cuirquit. I don't have problem with mother board or power suplay,:I've got 24v, &enable 5V.If you've got schematik, help me.
I replaced all caps in power suplay & inverter board.I have ESR meter .
How do I disable protection?? For inverter???I think problem in protection itself.
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