haier le42b1380 power supply issue

[freakaftr8]

Re: haier le42b1380 power supply issue

Way cool! I'm tearing into the panel tonight to see what I find.

[freakaftr8]

Re: haier le42b1380 power supply issue

okay so I Got into the panel last night and found out that all the LEDs are working and there's no shorts. However one strip was dimmer than the others I swap that strip to another pin and now the other strip Is dim. .

that Schottky barrier diode that burned out was an SR360 which is a 60 volt 3 amp. I replaced it with it only thing I could find and SR506 which is a 60V 5 amp. is there any possibility that this is throwing the balancer off since there are two of them one runs two connectors and the other one runs the other two connectors

[budm]

Re: haier le42b1380 power supply issue

"SR506 which is a 60V 5 amp" Higher current rating is fine.
The rectifiers are for the boost converter circuits outputs, so you need to check the DC Voltage on the Cathode side of those diodes to see if one is showing less Voltage than the other.
The typical LED drive circuit is that the Voltage is boosted up and then fed to the Anode pin of each LED strings, the Cathode side of each strings (if there are four individual strings) is connected to the Drain pin of the Power MOSFET, the Source pin is connected to the current sensing resistor, another end of the resistor is connected to ground, the sensing resistor is used for feedback to maintain steady current through the LED strings.
The Gate pin of the MOSFET is driven by the PWM signal for controlling the brightness.

[freakaftr8]

Re: haier le42b1380 power supply issue

I have the panel out again I started probing the positive red leads going into the LED backlights I found one short it on the left side I remove the short as the red wire head rubbed into the side frame and I still get a brief flash of the LED lights although they're all bright and 12 volt brief to the main board also but the TV will not stay on just a quick pulse and that's it.

so it was a very intermittent short I would not show up sometimes but when you flexthe TV would show up another time

[freakaftr8]

Re: haier le42b1380 power supply issue

okay so I had found a bad SMD resistor that runs off of the diode that was shorted. It was a 160 k Ohm what do you think the chances are that since I had a short in one of the LED strips that I might have destroyed the LED driver on that bank? Would the panel attempt to light up under a bad LED driver?

[budm]

Re: haier le42b1380 power supply issue

"I have the panel out again I started probing the positive red leads going into the LED backlights I found one short it on the left side" Are you saying that the red lead is shorted to the chassis?

[budm]

Re: haier le42b1380 power supply issue

OK, I look at the pictures of the bottom side of the board around the LED Driver boost converter power supplies.
There are 2 pairs LED strings, each pair has two LED strings connected in series and driven by its own boost converter power supply.
As you can see, there are two rectifier for each filter cap to supply the + Voltage to the ANODE of the string. Those two cap should have the same Voltage reading when the TV is turned on. You can also see two SMD IC, can you get the P/N?
So the diode may have been damaged when the Anode is shorted to ground which can also damage the MOSFET, that is why you need to check the DC Voltage at the Cathode of both diode to see if they put out the same voltage.

[freakaftr8]

Re: haier le42b1380 power supply issue

hi bud. Yes I have checked the anodes of both diodes and I'm getting roughly 38 volts on each side so it looks like the booster circuits are working properly however if you look at the picture I know it's hard to see but right out of the anode side of the diode right before it there is a small SMD resistor and a SMD capacitor the SMD resistor is a 160 k. the resistor was open on the diode side that blew so I replaced it. The SMD caps however seem to test ok in circuit. What I'm curious about is I hooked up the LED strips to a completely repaired power supply and I'm curious to think if something else had gone bad although the MOSFETs for the booster circuits are testing okay still of course I have no way to test the LED driver IC

[budm]

Re: haier le42b1380 power supply issue

Are you talking about these caps and resistors?

[budm]

Re: haier le42b1380 power supply issue

BTW, can you read the P/N on the ICs so we can look up the spec sheet to see how it works?

[freakaftr8]

Re: haier le42b1380 power supply issue

Yes on the cap but the resistor is the one before the cap right off the anode side of the diode . they are labeled 1603. I know it's hard to see though.

what IC do you need the part number for? The LED driver ic'S?

[budm]

Re: haier le42b1380 power supply issue

They are RC snubber for the diode, the circuit will still function without them in place. The two 160K are connected in parallel to give 80K resistance. https://cdn.badcaps-static.com/pdfs/...bf1cc12e6f.pdf
"The LED driver ic'S?" Yes, there are two of them, one per two LED strings. They look like are made by TI from looking at the Logo.

[freakaftr8]

Re: haier le42b1380 power supply issue

*led controller ics are 13408y tl494c

[budm]

Re: haier le42b1380 power supply issue

They are not using LED driver/controller?
https://cdn.badcaps-static.com/pdfs/...88cd5e8891.pdf

So both ICs have the same P/N?
https://www.badcaps.net/forum/attach...7&d=1416623866

[freakaftr8]

Re: haier le42b1380 power supply issue

Yes they do. Those ics are not led controllers?

[freakaftr8]

Re: haier le42b1380 power supply issue

Should I be checking pin 9 and 10 on both of those ccontroller Ic's for a possible error or voltage their meaning an error?

[freakaftr8]

Re: haier le42b1380 power supply issue

Are those tl494c not led driver controllers?

[budm]

Re: haier le42b1380 power supply issue

They are PWM IC primary designed for power supply control for switching power supply, but it is being used for controlling the LED drive circuit instead in this TV.

[freakaftr8]

Re: haier le42b1380 power supply issue

Ok well I can't seem to get the power supply to stay on long enough to test the voltage on each side of the cathode on the diodes. It just doesn't stay on long enough it's a quick Blip of voltage that's it. Regardless if the LED strings are connected or disconnected from the power supply.

[freakaftr8]

Re: haier le42b1380 power supply issue

okay so I did some more testing of components on the board over the weekend and I have noticed that maybe I overlooked before out of the 4 LED output connectors the first and the third connector get roughly 35 volt for the brief moment it turns on output tWo and four don't get any without the LED strips connected.

essentially LED output 1 & 3 are the only outputs that deliver the 38 volts with no strips connected

with the strips connected the anode side gets about 14 volts on two and four.
now this is most likely due to the fact that they're wired in series? But that would lead me to the fact that the voltage carried through the first strip into the second would there be that much of a voltage loss? Or am i finding something wrong now