Vizio E420i-AO tech help?

[HGSR]

Re: Vizio E420i-AO tech help?

Also, I forgot to state there was no video signal input to the tv. If that matters, let me know. I'll redo with a cable from the cable box connected and a tv station playing.

Sure is looking like an open load on L1. Guess we'll find out when I open the screens up to get to the LEDs. Am I thinking right?

[HGSR]

Re: Vizio E420i-AO tech help?

Bud,
Here's. My readings following your directions exactly I believe:
- AC cord remained connected throughout the testing
- LED cable remained connected to the board throughout all tests
- BLACK meter lead was connected to the metal chassis
Pin
L1- set power-off .39v (went to zero if I touched the metal chassis with my hand)
set powered on .008v no initial spike I could detect

L2- Set powered off. .39v (went to zero if I touched metal chassis with my hand)
Set powered on. 54v initial spike decreasing to 8.4v

[HGSR]

Re: Vizio E420i-AO tech help?

Oh. I see my error. You said L1- and L2-
I'll check that tomorrow. I did that check once before. I seem to recall the voltage floated on those pins but I'll verify and report back.

Re: wrong data.
You are correct. I Apologize.
/h

[budm]

Re: Vizio E420i-AO tech help?

"Oh ok. 67.1 on both 1&2 Doesn't matter if the connector is connected or not." so the reading are for L1- (MINUS), L2- (MINUS)?
If the connector is not in place then you should not have any reading on the L1- or L2- because there will be not current return path through the LED since it is not connected.
So are you sure you follow my instructions, wrong DATA does not help.
You have L1+, L2+, L1-, L2-. We already know what the L1+, L2+ already per previous posts.

"The active, normal voltages should be 100v and 80v if all is well. " That will be the result if there are loads connected, if you have open circuit then the power supply will jump up high then shutdown.

[vinceroger69]

Re: Vizio E420i-AO tech help?

is this the same voltage on the 1- and 2- side as well as im not sure if budm wanted the plus or minus readings so best take both

[HGSR]

Re: Vizio E420i-AO tech help?

Oh ok. 67.1 on both 1&2.
Doesn't matter if the connector is connected or not. Voltage readings are the same on Vout1+ and Vout2+
The ramp to 128v and decrease to 67.1.
According vto the ShopJimmy video in this model, one side drives 3 strips and one drives 2 strips. The active, normal voltages should be 100v and 80v if all is well.
On the 4 boards I have installed and measured all have read 66.7-8v or 67.1 at stasis.
/herb

[budm]

Re: Vizio E420i-AO tech help?

l1- and l2- is the led connector pins

+1, those are the labels for the LED connector pins, sorry for not being clear.

[vinceroger69]

Re: Vizio E420i-AO tech help?

l1- and l2- is the led connector pins

[HGSR]

Re: Vizio E420i-AO tech help?

Ok. I'll locate L1&2 and report back. Im assuming those are coils.
I don't have a schematic of this BD so I'm guessing a lot.
I'm a little gun shy having already cooked one ps BD.

Don't ever get old.
/herb

[budm]

Re: Vizio E420i-AO tech help?

I do not believe you try this test yet:
1) Leave black probe on the chassis, red probe on L1- then turn the TV on and record the dcv reading, then turn TV off.
2) put red probe on L2- then turn the TV on and record the reading.

[HGSR]

Re: Vizio E420i-AO tech help?

The 66 VDC is the input Voltage feeding the Boost converter circuit, when the Boost converter not running then you will see that 66 VDC on the output of the Boost converter, you will understand why that is when you look at the diagram of the boost converter circuit, right now the boost converter did run and and gave you the boosted Voltage but it went into protection shutdown either due to shorts or open circuit so the output drops down to 66 VDC.

Got it. Excellent! Thanks Bud. Makes perfect sense. I'll bet it's an open since the initial ramp goes to 128v before clamping to 66v. Do you think a short or open on one side of the dual output would cause both sides to go into protection?
Looks like I'll be replacing the LED strips. Want to test them before I pull them though. Just so the next guy that has this problem might have a fighting chance.
Again, Thanks.
/herb

[HGSR]

Re: Vizio E420i-AO tech help?

MUTE SCREEN ?!?!?!?

Found this on the VIZO site. This is what is scaring me about my problem. I'm concerned there is some setting somewhere I can't see. If I knew how to "reset" the darn thing it might help. Then, sanity returns and I remember I replaced the logic board. And yes, I tried this and nothing changed. But it is exactly how this set is functioning.


FROM VIZIO web site:
If there is no video but you have audio or you have intermittent video:
Press and hold the mute button on the VIZIO remote for 3 to 5 seconds. Some VIZIO TV's have a "Mute Screen" feature that turns the screen off if you are streaming an audio application (Pandora, Spotify, etc) and don't want the screen on. To activate/deactivate this feature, hold the mute button for 3-5 seconds.
Turn the TV off and unplug it. Press the power button on the side of the TV for 30 seconds. Let go of the power button and plug the TV back in.
Check the connections between the TV and device. Ensure the cord is connected securely to the TV and the source device.
Try a second device. (Example: If the issue happens on a Cable/Satellite box, try using a DVD player or gaming system to see if the issue occurs there.)
If the issue occurs on multiple devices there is an issue with your TV. Please contact Support by Clicking Contact at the bottom of the page or give us a call Monday - Friday from 7am - 11pm Central Time or Sat. & Sun. from 9am to 6pm Central Time at 855-833-3221.
If the issue only occurs on one device the issue is not with the TV but with the device or the cables used to connect it to the TV.

[dick_barton]

Re: Vizio E420i-AO tech help?

That's an excellent price. It is not unusual to see led strips advertised at that price per strip when there may be a total of 4 or 5 strips in the set so can prove very expensive to replace all the strips.

[budm]

Re: Vizio E420i-AO tech help?

The 66 VDC is the input Voltage feeding the Boost converter circuit, when the Boost converter not running then you will see that 66 VDC on the output of the Boost converter, you will understand why that is when you look at the diagram of the boost converter circuit, right now the boost converter did run and and gave you the boosted Voltage but it went into protection shutdown either due to shorts or open circuit so the output drops down to 66 VDC.

[HGSR]

Re: Vizio E420i-AO tech help?

Your point is well taken. That $49 kit from ShopJimmy.com will replace all 5 LED strips with all new ones. So $49 is the total cost if I order from SJ. I'm still going to wait for that LED tester to arrive before I open the screen or order new strips. I want to know if the strips are bad and causing this 66v LED driver voltage problem. No one else has solved it yet and it's not uncommon. Maybe someone else can benefit from this effort.

I'm finding that you can beat the prices of ShopJimmy on eBay but for convenience and customer service, SJ is pretty good for some parts.

[dick_barton]

Re: Vizio E420i-AO tech help?

The problem with your reasoning is that if you are considering replacing any faulty led with a replacement led strip, and more than one led strip within your set has a faulty led, then the cost starts mounting up. However if you intend to use the leds from a replacement led strip to do the stacking method (search Forum) then it does keep your costs down.

[HGSR]

Re: Vizio E420i-AO tech help?

Good input. Thanks Bud and Dick. Have done the panel removal research and there are videos on doing that to this model. I'm comfortable doing it. I'm an OLD electronics tech from the discrete component days. The first computer I worked on had tubes in it, as did the last TV I worked on ;-) In those days we detested doing "board swaps" to fix a problem rather than trouble shooting it. We found the bad component and repaired the board, replacing the bad tube, capacitor, transistor, diode or chip (they were new technology back then). So this stuff doesn't scare me. I just haven't done much of it since 1972.

Interestingly a complete set of replacement LEDS for this unit are $49.95 from Shop Jimmy. Given my level of investment to date, I could replace the entire LED array within my budget for this repair. The only issue is, what else could cause this problem that I haven't considered. So its $50 bucks to test the LEDs or $50 bucks to replace them all and hope the problem isn't in both power Distribution strips.

UPDATE - found LED testers on eBay for $35 and ordered one.

I hate just throwing parts at a problem but since I don't have a lab or power source to test these LEDs, I'm not sure what else I can do. I mis my old Tectronic Dual Trace scope.

Sure hope its not something stupid like a setting. Changing the Logic bd out should have eliminated that. I've even tried multiple using VIZIO remotes. No change in symptoms.

Any other suggestions are greatfully welcomed.
/herb
An OLD ET.

[dick_barton]

Re: Vizio E420i-AO tech help?

Take the advice freely given by Budm.
Unfortunately it does look as though you will have to remove the panel and filters below it carefully. Do not mix them up and store them in an order you know they go back in.

The led tester is an excellent tool for testing leds and I'm sure you could sell it on if you don't wish to keep it. The problem is that if one led or connector is open circuit then the whole strip will fail to illuminate however the led tester allows you to test individual leds to find which ones in the string are faulty.

It would be worth your while taking some time out to search Youtube for videos on removing the panel and how to test the leds of which there are plenty.

[budm]

Re: Vizio E420i-AO tech help?

You should buy the LED tester such as the one sold by shopjimmy, about $50 investment.
You are going to need power supply with more than 100VDC with current limiter to about 20~30mA to start with.
BTW, never connect power supply directly to the LED without current limiter.

[HGSR]

Re: Vizio E420i-AO tech help?

AHA! Thanks Dick. Could you give me a hint what to do a search on or how trouble shoot to verify the problem. Is there a way to use a meter at the cable connector end? Otherwise I'm assuming I'll need to open the screeens to get to the LEDs and driver strips. I don't have a 24v DC power supply so I thought maybe I could Isolate each half of a strip (by unplugging them from the boards and each other, and use a 12v battery to test them. Not sure how to check the driver/distribution strips that are fed by the LED cable of the PS bd. Does this sound reasonable?

I've found one other thread on this no backlight problem where the LED driver voltage was 66v but there was no solution given. The thread just died. So I'm stumped.