Samsung LE32A336 red light blinking

[coolizard]

Hello,
I have a samsung LE32A336. I am sure that a repaired whole PSU, because I tested all voltages on their nominal current. Everything's fine, until I connect main board, then StandBy supply (5.2V) started oscillation between 5,2V and 0 (it is a reason why red led blinking). I think, it is because on the mother board is shortcut, but I cannot find where. I changed all elites, but does not help. I am thinking about corrupted EEPROM, but it cannot shortcut supply, am I right? BTW, when I connect resistor between StB supply and ON/OFF pin on PSU, TV works fine, but it is not good way . Any suggestion please? Main board is: BN94-02117.

[Agent24]

Re: Samsung LE32A336 red light blinking

That problem sounds rather odd, if the TV works OK when manually starting the PSU.
What do you measure on the 5.2v rail voltage when you do that?

Can you post photos of your boards etc?

[budm]

Re: Samsung LE32A336 red light blinking

What resistance do get get when measure between GND and the STBY pin of the main board?
How much current did you pull on the stby power pin? 0.5A, 1A?

[coolizard]

Re: Samsung LE32A336 red light blinking

Hello,
new information is, that TV is down even if I manually start PSU, so there must be something dead on CPU board and I cannot measure stby voltage while CPU brd is connected. I attached pictures.

Resistance between GND and STBY on main board is more than 1M (some capacitors charging and resistance is going higher and higher).

I tested STBy pwr on 0,6A it should be nominal because it is written on board.

[budm]

Re: Samsung LE32A336 red light blinking

The overload of the STBY power supply can be at the output side of the Voltage regulators ICs. I would start checking the resistance between the two legs of the filter/bypass caps to see any one of them shows really low resistance.

[coolizard]

Re: Samsung LE32A336 red light blinking

I tested all elit caps and some ceramical but without succes. I also remove them and test externally for capacity, everything looks fine. On the output of one LDO (is still on the board) I measured resistance 300ohm, but I dont know if it is bad or not. Any other idea please? Am lost .

[Agent24]

Re: Samsung LE32A336 red light blinking

It's a little hard to say. at 5v or 3.3v or so, 300 ohms does not present much of a load - only a few milliamps. And if the rail is powering a large ASIC\CPU etc then a low resistance is not an unusual thing - but, it could be indicative of a leaky component on that rail too, which only breaks down when the full operating voltage is applied.

Can you identify all the LDOs or other regulators which run directly off the 5v2 STBY rail? - and can you show close-up photos of the board area for each one?

[coolizard]

Re: Samsung LE32A336 red light blinking

Hello,
I found two LDOs directly on 5V2 rail, one is under the shiled, it is a reason, why I am late, it is not easy to pull shield off. Look at pictures please.

[budm]

Re: Samsung LE32A336 red light blinking

You are seeing the resistance of the resistor network for setting the LDO output Voltage.

[coolizard]

Re: Samsung LE32A336 red light blinking

Hello together,
I have some new measurement. When I connect CPU board to external supply, the consumption is almost 800mA on 5V (stby power) for about 2s, then it stabilises on 50mA. I think problem is, that the 5V on PSU board has maximum 600mA and if something takes 800mA, it turn off and on again. I checked all elits on main board and also removed all LDO one by one, but everything looks fine. Any idea please?

[Agent24]

Re: Samsung LE32A336 red light blinking

So with all LDO removed the 5v2SB rail still power cycles?

What is the current draw?

[coolizard]

Re: Samsung LE32A336 red light blinking

Hello,

I removed LDO one by one, but always put them back, if it doesnt help. So I dont know current draw without all of them. Now with all LDOs it takes 800mA.

[coolizard]

Re: Samsung LE32A336 red light blinking

Hello again,

I have new info. CPU PCB works well for now, but PSU is dead again :/. It start working only if I heat up IC STR-A6159, just touch this IC with solder and it power on. How is it possible? I changed this IC as one of first parts before 4 month.

[Agent24]

Re: Samsung LE32A336 red light blinking

Are you sure it's heat? Have you tried a hairdryer or similar to see if you get the same results?

Did you touch the IC body or a pin, and if so, which pin?

Did you touch it with the soldering iron while the PSU was powered up or off?

[coolizard]

Re: Samsung LE32A336 red light blinking

Are you sure it's heat? Have you tried a hairdryer or similar to see if you get the same results?

Did you touch the IC body or a pin, and if so, which pin?

Did you touch it with the soldering iron while the PSU was powered up or off?

Yes I am sure. I used hot air (set on 150 degrees) for soldering with very thin tip and it works.

I also tried touch (IC body) with soldering iron and it works too.

All tests was on powered PSU and I was checking output of PSU on oscilloscope. PSU pulsing until I heated A6159. All caps around are new, even SMD.

[Agent24]

Re: Samsung LE32A336 red light blinking

Try another A6159?

[coolizard]

Re: Samsung LE32A336 red light blinking

Try another A6159?

It was last one. I order few pcs from china, but it will take a month. Other idea?

[Agent24]

Re: Samsung LE32A336 red light blinking

It could be some other part nearby. SMD ceramic capacitors can get cracked easily during soldering, you could check those, especially if you replaced them. If you are replacing them, use hot air to solder them and not the soldering iron.

You might want to try ordering known genuine IC from a good shop like http://www.digikey.com/product-detai...159-ND/3929382

China is not always good...

Also, have you checked the VCC supply capacitor for your STR-A6159 IC? It maybe high ESR or otherwise bad.

[coolizard]

Re: Samsung LE32A336 red light blinking

Hello again,

finally I repaired PSU, it was bad diode in 5.2V stb snubber, red LED lights continously now. TV also worked for few ours, but after I turned TV off, I cannot turn it on again. Something must be dead on CPU board now .

Any idea? On CPU board I changed all elits.

Edit:
Of course I measured all voltage rails, they are OK.

Edit2:
interesting, on CPU board is small 1uF elit, I measured 30V on him. How is it possible? The highest rail has 12,3V.

[coolizard]

Re: Samsung LE32A336 red light blinking

SOLVED!!
I forgot to writte how it is done, but late is better then never . It was wrong current measuring resistor for STR-A6159 IC. On that resistor was different voltage drop than it should be, so the STR-A6159 thinked it is ovecurrented. Do not measure this resistor with multimeter! Remove him from PCB and measure voltage drop for 1A current. TV works fine for almost year .