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

[zameelm]

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

I have a plasma TV with the same problem with the same PSU (LJ44-00133 A). I checked the Vin (pin 1) of the voltage regulator with a multimeter and found to be zero. Pin 4 reads 2.8v. I have very little knowledge of electronics. Please help!

[Djihatch]

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

Hi,

Just a little feedback, it may help someone ;-)
The TV is working fine for one month now.
I just replaced the the 4 pin regulator (the fourth pin was a on/off feature) with a common 3 pin regulator (I had to bend pin 2 and 3 for the pinout match the pcb one ). Before doing this, i checked how on/off feature was controlled and realized that it was directly connected to power trought resistors (no ICs), wich meaned that its state was always to on.
I assume that some manufacturers buy end of sale components in large quantities, even if some components features are unused, to reduce prices.

Thanks for the help provided by this forum.

Djihatch

[Djihatch]

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

thanks for the tips to both of you.

[PlainBill]

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

Thanks Plainbill,

I added location in my profile ;-), unfortunately, I live in France, so shipping will be increased for me.
How did you do to find an equivalent ? I searched for hours and no way...
At least, you suggested me and equivalent. I hope that it will be easier to find even in France.
As I'm curious, I used a 3 pin equivalent voltage regulator, and it worked for 20 minutes (it could work longer, but now that I'm sure that this voltage regulator is the only faulty component, there's no need to test it more).
this regulator is not controled by an IC. It's switched on with relays and resistors. I'm not good enough in electronic to be sure that there's no need for this voltage regulator to be controled. I think that if the designer decided to use a 4 pin regulator instead of a 3 pin (and cheaper !) regulator, that's for a good reason.
I'll try to find a cheap controller available in France and I'll let you know.

Thanks again.

The whole basis of finding equivalent parts is that no manufacturer wants to use a single-source component unless THEY control the production. The common practice is each company will use their own two or three letter prefix, the divider character is usually the same, and the meaning of the trailing characters will vary with the manufacturer.

There are a couple of steps to go through on exercises like this. First, I went on DigiKey's web site and tried selecting equivalent parts by the critical features - 15V, 1A, LDO, TO-220 package with 4 pins. That didn't bring up any hits.

Next, I stripped the part number down to it's significant part - 75R15 added datasheet and Googled that. That took me to alldatasheet.com, which gave me the original part number and the Fairchild part number. Since Digikey had drawn a blank, I next tried Mouser with the full part number, and hit paydirt.

PlainBill

[PCBONEZ]

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

http://www.google.com/#sclient=psy&h...w=1280&bih=839

Compare specs to LM2940/LM2940C and see if RS has some of those.

.

[Djihatch]

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

Thanks PCBONEZ, but this component is not available :-(

[PCBONEZ]

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

Check here:
http://www.rs-components.com/index.html

[Djihatch]

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

Thanks Plainbill,

I added location in my profile ;-), unfortunately, I live in France, so shipping will be increased for me.
How did you do to find an equivalent ? I searched for hours and no way...
At least, you suggested me and equivalent. I hope that it will be easier to find even in France.
As I'm curious, I used a 3 pin equivalent voltage regulator, and it worked for 20 minutes (it could work longer, but now that I'm sure that this voltage regulator is the only faulty component, there's no need to test it more).
this regulator is not controled by an IC. It's switched on with relays and resistors. I'm not good enough in electronic to be sure that there's no need for this voltage regulator to be controled. I think that if the designer decided to use a 4 pin regulator instead of a 3 pin (and cheaper !) regulator, that's for a good reason.
I'll try to find a cheap controller available in France and I'll let you know.

Thanks again.

[PlainBill]

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

Hi,

I've built a test circuit for the voltage regulator... And it has exploded !!! I have to find a new one (I found some of these in china but they cost 20 $ + 15 $ shipping !!!).

Let me know if you have cheaper solution...

Thanks.

Pin 4 of the KIA78R15P switches it on and off. Was that function used, or was the control pin held high by a resistor?

Forget that!! The equivalent part is available from Fairchild as KA78R15C.

The good news (if you live in the USA) - it is available from Mouser as item number 512-KA78R15CTU.

The better news is they have 12,706 in stock.

The best news is they cost $0.95 each.

The bad news is shipping will cost about $5.00

And this is a good opportunity to suggest you add your location to your profile. It makes it easier to suggest a meaningful supplier.

PlainBill

[Djihatch]

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

Hi,

I've built a test circuit for the voltage regulator... And it has exploded !!! I have to find a new one (I found some of these in china but they cost 20 $ + 15 $ shipping !!!).

Let me know if you have cheaper solution...

Thanks.

[joshnz]

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

The output of the psu will be fed into the regulator to provide a regulated supply that is why that regulator is the to take the 20 volts to make nice and smooth 15volts.

[joshnz]

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

oh i see what you ment the input to the regulator does not need to be regulated

[Djihatch]

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

thanks,

I've built the test circuit but I have no regulated supply at home. I'll grab one at work tomorow and let you know.
Have a nice day (or good night ;-)

[joshnz]

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

yes should be regulated.
The regulator is designed to provide 15volts at 1 amp with a vin of 15.5 volts or greater up to 30 volts.

Looks like it is faulty.

[Djihatch]

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

I get 20.3 V on Vin pin. Unfortunately, I don't have the schematics of this PSU, so I don't know if it's correct. I assume that if it's more than 15v, it should be regulated.

Thanks

[joshnz]

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

Are you getting Vin from the tv?

[joshnz]

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

Here is a example test circuit.

[Djihatch]

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

I used a 250 ohm 1 W resistor between Gnd and Vout. I've measured 11.3 v instead of 15. with this resistor, I should have 6 mA at 15 V (Vout). I'm just above load regulation that is written in the datasheet (5 mA to 1 A) so it should work.
2 options : the regulator is bad or Vin supply is bad and doesn't support load. I'd like to put a dummy resistor between Vin and ground but as I have no schematics, and I don't want to burn something.

++

[Djihatch]

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

Thanks to both of you.

In fact, the voltage regulator is out of the PCB (for the measurement to be easyer), but the wiring is still the same. I assume that the design of this board is good (with corrects capacitors), so the Vout should be correct too...
for the test, what kind of capacitor should I use ? how should I solder them ? (first between ground and Vin, second between ground and Vout ? 1 unpolarized cap between Vin and Vout ?)

Thanks again

[PlainBill]

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.

Correct. However, the measurements suggest the regulator is bad. Djihatch can try adding bypass caps at input and output as you suggested which should take only a few minutes and would confirm this.

PlainBill