VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

[triplefour]

normal standby voltage readings when plugged in.

pressing power button turns the white power LED on
but pressing power button again will not turn the set off.
voltage on LED connector with all boards connected normally:
LED1: 0
VOUT1: rises and falls continuously (fluctuates) between 92 and 98
LED2: 0
VOUT2: rises and falls continuously (fluctuates) between 136 and 146

readings on the connector that go to the mainboard seem normal but there is some .1v fluctuation on some of the outputs if i observe long enough
PWM1:2.7
PWM2:2.7
BLU ON: 3.3
PS_ON: 3.3
12V: 12
12V: 12
GND:0
5V: 5.2
5V: 5.2

PWM'S are .9 in standby. all other pins 0 except 5v is 5.2v

when forced on, without MB connected the voltages on pwm's and BLU_on and PS_on are all 5.2 and the 12v lines are only at 11.5

the fluctuating VOUT1 and VOUT2 for the LED strings give the same readings no matter whether MB is connected or not, whether LED connector is connected or not, and whether the PSU is forced or not.

using LED tester i see that
LED1+VOUT1 (red on vout, black on led) i see the strips light up (through the holes in the case)
and the meter reads a fluctuating voltage between 53.5 and 54.1, eventually almost settling competely to 53.5 plus or minus .1 ...it never settles all the way
LED2+VOUT2 i see the same fluctuating and not settling but worse, and its between 95 and 98 and keeps fluctuating wildly between those 2 values.


i read in another post that normal operation of this set is supposed to be 80v for one of the strings and 100v for the other, but in that same thread the guy had 65v on both outputs whether connected to LED's or not), even tho he changed the PSU like 3 times, and it turned out to be just bad LEDS and after changing those, his set worked fine. totally confusing as to why it was ok with only 65v on those outputs when its "supposed to be" 80 and 100 because there are a different number of strips on each line...

to summarize and explain the title of this post:

fluctuating voltage with my LED tester on the strings makes me think bad LED's

fluctuating voltage at the LED output connector even with nothing connected makes me think bad PSU

and power light coming on but not responding to power off command even though MB appears to have all the voltages it needs makes me think bad MB.

could i really have a trifecta on my hands here??

another "interesting" thing to note (and LOVE vizio for) is that even though this tv differs by only one measly number from the E420i-A1, and the chassis look exactly the same, its a COMPLETELY different tv with 3 completely different boards in it! THANKS VIZIO! SO MUCH FUN!

having fun as always, but can anyone help me have even a little MORE fun?
thanks!

[budm]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

Are you testing the Voltages at the LED connector with ref. to chassis GND?
I need to see the Voltage readings of all the LED connector pins (LEDs in place) with ref. to GND. when the TV is first turned on and 5 seconds later, which mean you need to leave the probes connected BEFORE turning on the TV, it also means you will have to do that for all 4 pins.

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

thanks budm. yes i was using chassis ground as a reference, and im pretty sure i tested them like that but ill do it again and make sure the probes are in place with the TV off before i turning on and report back what i find.

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

ok i did what you said but i didnt see any difference. voltage for the vout's jumps up to its fluctuating voltage immediately. it doesnt go higher and then drop.
the other 2 pins read 0 always, before during and after power on...

[budm]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

ok i did what you said but i didnt see any difference. voltage for the vout's jumps up to its fluctuating voltage immediately. it doesnt go higher and then drop.
the other 2 pins read 0 always, before during and after power on...

LED1: 0
VOUT1: rises and falls continuously (fluctuates) between 92 and 98
LED2: 0
VOUT2: rises and falls continuously (fluctuates) between 136 and 146

That is not making any sense, Vout 1, 2 are the boosted Voltage out put from the two boost converter circuits to feed the Anode of each set of the LED string (there are two large LED strings), the LED1 is the CATHODE return of the LED sting 1, LED2 is the CATHODE return of the LED string 2 so I expect to see some Voltages (10~20VDC) there if the LED circuit does not have open circuit.
The LED tester is only putting out about 30mA, the led driver board will drive the LEDs at 200~300mA which at that level the bad LED cause the problem to show up but not at lower driving current when using the LED tester. I am suspecting bad LED in the number 2 string.

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

ok guess ill take apart the panel and see which LED's are bad

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

ok i took the panel apart and i did find 5 bad LEDS. there are 5 strips of ten lights each in this panel. LED1 and VOUT1 power the top and bottom strips, and LED2 and vout2 power the middle 3.

here is a picture i drew to show which LED's failed.


so i guess ill just...repair these LED's and see what happens?
i've been getting pretty good at repairing LED strips.
fixed 3 LG panels recently. first one took me hours. 3rd one took me minutes

[budm]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

Sounds good to me.
You said bad LEDs, in which kind of bad? shorted or flickering, etc. when test with your tester individually.
I am beginning to see the weakness of the LED tester due to its low drive current capability, you can use it and it will show the LED string to light up but it will not show if the LED has shorted LED/s or not. The bad LED (not shorted out) may also light up at 30mA but when it is driven by much higher current it will fail.

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

are you saying i avoid this problem if i test individually each LED?

[budm]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

Right I need to find out as to what you have found bad on those bad LEDs, they fail to light up, or what?

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

yes the 5 bad LED completely fail to light up even when i apply power directly to just the single LED. somehow when lighting the strings with the tester though, the bad LED's are just skipped over, allowing the rest of the LEDs to light up. they glow soft at first but then climb in voltage to 2.8 and then stop at what looks to me to be "full brightness" are you saying that in actual operation of the tv they will be even brighter? as it is they are hard to even look at !

[budm]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

They will be really bright when driven by the TV LED driver circuit.

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

ok im going to replace these LEDs tonight and will let u know what the result is tomorrow. thanks!

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

ok i replaced all 5 bad LED's which were shorted closed. and now with my LED tester, the strings light up just fine, and the voltage no longer fluctuates as much. barely at all
and when it does its just by .1
55.5~55.6v for string 1 but after a while it just stays solid at 55.5
83.6~83.7v for string 2 but after a while it just stays solid at 83.7

readings from the LED connector of the PSU havent changed much from previous posts.
tests are done with PSU tricked on via PSON and BLUON
and with the LED's connected i get:
VOUT1 fluctuating up and down from 105 to 111 on string1
VOUT2 fluctuating up and down from 147 to 157 on string2
and steady 0 on the black wires (LED1 and LED2)
and with the LED's not connected i get the same fluctuating voltages:
VOUT1: 98~104v
VOUT2: 147~157
and the black wires are still 0 always
not sure why VOUT1 is getting a few less volts with the string disconnected :/
also not sure why the voltages have changed at all from previous posts, as i have done nothing to the PSU and the LED's arent even connected in one of the tests...

pretty sure ive at least got PSU issues here, but what should i look at to cause a fluctuating voltage?

in normal operation, the PSU should boost up to those voltages but then settle back down to something like what i see on my LED tester as the required voltage for the strings? but as its falling down to the right value, it gets boosted back up in a repeating loop?

[budm]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

Those readings indicate open circuit in the LED strings.
If you pull the LED connector from the board and use the LED tester probe right at the LED connector that you remove from the board, do the LEDs come on for each string?

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

yes, that was the first thing i did. they all light up.

[budm]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

Do you still have the panel open so you can check the resistance right at the LED connector's pins which are soldered to the board and the end of each wire that goes to the LED strip? We want to make sure we have connection right from the pin soldered to board all the way to the LED strip. There is no way to have 0 V on the return wires LED1/2 of the LED string with that much Vout1/2 feeding the LED strips.

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

hah idk why i didnt think of that, as i've been applying this fix to 3 other LG panels i was working on. this vizio uses a LG panel so i guess all LG panels this is a thing to look for. the connector somehow doesnt make good contact with the PSU pins. i put some extra wire inside each hole of the connector and plugged it in, and now when i trick the PSU i get full backlights! and yes they are much brighter than my LED tester can make them.
and now that the PSU is behaving properly, so is the MB. i can use the pwr button to turn the set off now wheras before it wouldnt do anything but turn it on. now to put the panel back together and see a picture! hopefully!

[triplefour]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

its a beautiful day! we didnt get hit by north korean nukes, AND i fixed a tv! thanks budm for listening to me and poking me in the right direction as usual

[budm]

Re: VIZIO E420i-A0 has bad PSU, bad MB, and bad LED's (i think)

Glad to hear that it is fixed, when something does not make sense then you have think it through logically to see why you are not getting what you should get from point 'A' to point 'B'. You have Voltage going into one end but nothing coming from another end.