Vizio E470i-A0 - FL test ok, half bl working

[fcisolutions]

I didn't have backlights to start so I tested with my led tester from shopjimmy and got 2 different voltage readings even though both strips lit up (with the tester - not the power supply). I took apart the panel and sure enough a bad led strip (was pulling too much voltage). I replaced it and with the tester am now getting 73.5v on one string and 72.5 on the other. But when I connect to the power supply just 1 string of leds is working.

When I power on the set, I put my voltmeter leads on the led connector on the power supply and get:

Leds plugged in:
Vout1 -- 120-130v fluctuating
Vout2 -- 101v and stable

Leds not plugged in:
Vout1 -- 120-130v fluctuating
Vout2 -- 120-130v fluctuation

So ... Any ideas?

[dskall]

Re: Vizio E470i-A0 - FL test ok, half bl working

Open circuit on V1, bad connection on that string

[budm]

Re: Vizio E470i-A0 - FL test ok, half bl working

You have two set of LEDs and two LED driver circuits, it sounds like one of them has open circuit, if you swap the LED connections, the symptom should follow.

[fcisolutions]

Re: Vizio E470i-A0 - FL test ok, half bl working

Ok but I think it's V2 @dskall as V1 is the side that's working. So I'll swap the connections in the morning and report my findings. Thanks guys.

[budm]

Re: Vizio E470i-A0 - FL test ok, half bl working

Vout T1 should be the supply out that is connected to the Anode of the first LED in string one, the LED1 should the Cathode of the last LED in the string which is the return line of the LED string one which is connected to the Drain of the PWM ControlledSMD power MOSFET and then the current sensing resistor and then to GND return, if that string does have open circuit then you should see the Voltage on LED 1 PIN, same setup is applied to VoutT2 and LED2.

It looks like your board:
http://www.shopjimmy.com/vizio-0500-...upply-unit.htm

Pictures provided by shopjimmy.

[fcisolutions]

Re: Vizio E470i-A0 - FL test ok, half bl working

Ok great I'll ck those FETs in the morning too. Thanks for the direction. I'm new at troubleshooting a power supply.

[budm]

Re: Vizio E470i-A0 - FL test ok, half bl working

Ok great I'll ck those FETs in the morning too. Thanks for the direction. I'm new at troubleshooting a power supply.

I doubt that the MOSFET are bad they do not go out too often in that section since the typical current is only around 400mA at most, I am more interested in the Voltage of the LED return pins LED1, LED 2.

[dick_barton]

Re: Vizio E470i-A0 - FL test ok, half bl working

You have quite a few 0 ohm resistors around the SEM5028 IC that you can check out with the set off using your meter set to ohms.

[freakaftr8]

Re: Vizio E470i-A0 - FL test ok, half bl working

Also I should note that these sets like to have bad connections from the led to the strip. I've seen where LEDs oxidized underneath even though they test good with a voltmeter in diode check mode it doesn't necessarily mean that it's connecting to the board properly so in essence you have an open string

[budm]

Re: Vizio E470i-A0 - FL test ok, half bl working

BTW:
Leds plugged in:
Vout1 -- 120-130v fluctuating = No load present
Vout2 -- 101v and stable = Has load present

Leds not plugged in:
Vout1 -- 120-130v fluctuating = No load present
Vout2 -- 120-130v fluctuation = No load present

[fcisolutions]

Re: Vizio E470i-A0 - FL test ok, half bl working

@budm

With leds plugged in:
------------------------
Led1 --- 60-68v
Vout1 --- 120-128v
Led2 --- 0.9v
Vout2 --- 101v

With leds unplugged:
Both Vout1 &2 are 128v and LED1 &2 are 0v


@dick_barton

the first set of resistors were 1.5ohm and the other set 0.4ohms

[dick_barton]

Re: Vizio E470i-A0 - FL test ok, half bl working

So the resistors are OK. Looks like a led fault.

[fcisolutions]

Re: Vizio E470i-A0 - FL test ok, half bl working

Yes it was a bad led string. What threw me was the led tester showing near equal voltage readings. But when I went back in and individually tested each strip, I noticed one that would fluctuate.

Thanks to all that commented.

[dskall]

Re: Vizio E470i-A0 - FL test ok, half bl working

Just as an add on to this post. Just repaired this model. It had intermittent backlights. Found and replaced four bad leds. Still had intermittent failure on one string. By freezing ic 9101 SEM5028 was able to affect problem. Replaced SEM5028 all has been good for several hours now.
I also modified current going to led's. R9110 and R9210 which are 1.5ohm 1/2watt which output 420ma at max brightness. Replaced with 2 3.7ohm 1/4 watt in parallel witch brought down current from 420ma to 350ma. 2ohms on resistors should work good

[anthonystv]

Re: Vizio E470i-A0 - FL test ok, half bl working

I have an issue with this same exact tv and board First I replaced all the LEDS and IM running with no screen so I can see what is actually happening . there are 3 strips of leds in the center and 2 on the bottom and one on top they are driven by 2 seperate power supplys respectfully almost like a stereo amplifier .. CH 1 shows me with NO LEDS connected fluctuating from 125 to 132 v all the time ... CH 2 Flctuates from 122-125 3 times ... then shuts down to give me 66 v .. CH 1 will stay up ,,, there is an issue with this board it is NOT THE BACKLIGHTS ... .. with the backlights connected ... I get 105 CH 1 and 103 ch 2 THEN CHANNEL 2 WILL DROP IN ABOUT 10 SECS.. since the board reacts the same way with or without LEDS its not LEDS although I swapped them 7 ways to sunday with no differet results .. I also swapped Transfromers from CH 1 to Ch 2 No difference ... I just ordered a New board from SHOPJIMMY that board does EXACTLY THE SAME thing !! even the same channel drops and so now I ordered a power supply repair kit that contains the SEM5028 IC I think there known issue with these boards .. THE LEDS WERE BAD originailly But changed them they are all new now ... Anybody run into this ?

[anthonystv]

Re: Vizio E470i-A0 - FL test ok, half bl working

bump

[nomoresonys]

Re: Vizio E470i-A0 - FL test ok, half bl working

Make sure you have good solid connections in the whole backlight circuit.

[budm]

Re: Vizio E470i-A0 - FL test ok, half bl working

You did not provide the Voltage readings of all 4 pins.
What are they?
With LED's plugged in:
------------------------
LED1 --- ??v
Vout1 --- ????v
LED2 --- ???v
Vout2 --- ???v

[anthonystv]

Re: Vizio E470i-A0 - FL test ok, half bl working

105v LED 1
Retrun .7VDC
103 LED 2
Reurn Sometimes .7 vdc sometimes 6 v not sure why not sensative to touch also has no bearing on wether the channel shuts down or not
I have on occasion got it to stay up if the tv gets by the first 10 secs of start up iy will stay on for hours but turn the tv off and back on and drops again will drop with in 10 secs if its going to drop I have swapped the leds from ch 1 to ch 2 but ch2 always shuts down no matter what it hooked to it and eve if NO LEDS hooked to it it will shutdown while ch1 will stay up even with no leds hooked to it

[anthonystv]

Re: Vizio E470i-A0 - FL test ok, half bl working

The voltage on led 2 will fall slowly when it reaches around 99v the leds shut off and it falls to 66 v as the osc on the voltage doubler circuit was told to give up the question is why ?