42' plasma TV - Denver KTV-55 - Faulty power supply

[joshnz]

Re: 42' plasma TV - Denver KTV-55 - Faulty power supply

Pin 4 turns regulator on or off.
voltage greater than 2volts = on
voltage less than .8 volts = off

output voltage is low regulator need capacitors on input and output to give good voltage. Yes you can use a resistor to provide dummy load in your testing setup.

PlainBill was asking you to lift pin 1 and measure amps going in to the regulator from the board.

[Djihatch]

Re: 42' plasma TV - Denver KTV-55 - Faulty power supply

Thanks Plainbill

I unsoldered the voltage regulator an put it on a PCB like (I don't know how its called in english : The blank ones used in labs where you can put components and wires without soldering).
So I was free to perform all tests. I can't check the temperature because power is on during 1 second then the relays turn it off. So there is not enough time for this component to heat.
Here are the results, during the second when the power is on :
pin 1 (Vin - Dc input) : 20.3 V - 38 mA
pin 2 (Vout - Dc output) : 9.3 V (instead of 15 V) - 33 mA
pin 3 : Ground
pin 4 (On - Off control) : 6.3 V - 0 mA

If this voltage regulator,is driven by a current, this is obvious that it can't work with 0 mA on pin 4. What sounds weird to me is that there is 9.3 V and 33 mA on pin 2, it should be 0.

This component is still out of the board. Is it possible to put a dummy resistor instead of pin 4 to check if there's a significant current which would mean that pin 4 is open ?

Are they common failures on those kind of PSU that prevent voltage regulators to be set to "On".

Thanks again.

[PlainBill]

Re: 42' plasma TV - Denver KTV-55 - Faulty power supply

Thanks a lot. this website seems to be very interesting.

I found a KIA78R15PI (voltage regulator) that gives me 10 V (Vout controled with a scopemeter) instead of 15 V, wich may explain that the NCP1653 controler doesn't drive correctly the FETs.
Does that means that the voltage regulator is bad ? (That sounds weird to me, I thought that a bad voltage regulator should give the same voltage as Vin if shorted, or nothing is open but not another regulated voltage)
Does that mean that it is overloaded ? How can I chack that ?

Thank you.

The easiest way to check the current draw would be to unsolder pin 1 (input), then use an ammeter to measure the current the regulator is drawing. (Pin 2 would show the current the regulator is supplying, but pin 1 may be easier to access.) An even simpler method would be to check the temperature of the regulator.

If it radiates heat and leaves a blister on your thumb, it's overheating.

PlainBill

[Djihatch]

Re: 42' plasma TV - Denver KTV-55 - Faulty power supply

Thanks a lot. this website seems to be very interesting.

I found a KIA78R15PI (voltage regulator) that gives me 10 V (Vout controled with a scopemeter) instead of 15 V, wich may explain that the NCP1653 controler doesn't drive correctly the FETs.
Does that means that the voltage regulator is bad ? (That sounds weird to me, I thought that a bad voltage regulator should give the same voltage as Vin if shorted, or nothing is open but not another regulated voltage)
Does that mean that it is overloaded ? How can I chack that ?

Thank you.

[retiredcaps]

Re: 42' plasma TV - Denver KTV-55 - Faulty power supply

When I was in front of the TV's, they were obviously plasma TVs. They were cheap and my aim is to learn, so I bought them.

If anyone has and idea ;-)

The Coppell TV repair blog has some valuable info on plasma TVs over the last 2 years at

http://blog.coppelltvrepair.com/

[Djihatch]

Hi, I'm back with another problem ;-) I hope that someone will help...

I bought 5 TVs from a guy who thought that they were LCDs (I know a bit more about LCDs). When I was in front of the TV's, they were obviously plasma TVs. They were cheap and my aim is to learn, so I bought them. But now I need your help to fix them !

The PSU is a Samsung one : LJ44-00133 A (I seached a lot and can't find the schematics, if someone can help ;-) ).

The problem :
When I plug the plasma, the led panel is red (which seems to be ok)
When I turn on the plasma the led turns to green, I hear a relay turn on and off during a second but the panel stay green (that is strange because it usualy blinks red).
No way to turn it off and on again using the button : I have to unplug and replug the TV to hear the relay again by pressing the button.

-Fuses are OK.
-All eletrolityc caps are OK (unsoldered and tested).
I checked big FETS onboard and they're not shorted (As they are not easy to unsolder, I wait for your advices for easyer troubleshoot on other components before I unsolder them for accurate test)
- I assume that, as LCD TVs, there is a feedback using optos, etc... So I cheched what happens on transformers that separate hot from cold side (using a scopemeter). On hot side, nothing happens when I hear relays being on during a second. Obviously, the cold part is not supplied, so there is no feedback wich causes the relay to be off after one second (correct me if I'm wrong).
- I checked what happens on the FETS (gate) with a scopemeter and I think there's nothing significant. Maybe the signal is too low for me to catch him, or maybe there's a problem because FETS should receive something significant on their gates.
- I checked volts on connectors. Nothing on 12V and more connectors. I assume that this is "normal" because the cold part is not powered. only Vsb is OK on "low voltage" connectors. Other voltages are unsignificant (ex : 0.5 v where it should be 5 V).

At this point, I'm stuck ;-). I'm pretty sure that something prevent the first fets to let the power go ahead...
I could unsolder all transistors and ceramic caps to check them all. But it will take ages, and that may cause other problems (bads solders as an example).

So, If anyone has and idea about how to reduce the area to check (I'm pretty sure that the problem is in the hot part).
Is there a way to bypass some electronic controled parts (such as FETS) (with non destructive methods, of course !) to troubleshoot that board...

If anyone has and idea ;-)

Thanks by advance.

PS: I appologize for my poor english (I'm french).