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Old 03-16-2017, 12:11 PM   #1
HGSR
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Default Vizio E420i-AO tech help?

Folks, I could use some info.

A Google search on this model of VIZIO TV yields many LED and LED power supply issues. Also, YouTube provides many good LED tv repair videos. ShopJimmy.com even has a video on this very model and how to trouble shoot the "sound but no-backlight" problem. Been there, done that. My unit has sound, a dark screen, and passes the flashlight test - there is full video on the in-lit screen. I just don't have BACK LIGHTS. What none of the excellent troubleshooting sources provide are the answer to a couple of simple questions:

1. How can I test the LED strips of this unit without the slick ShopJimmy.com LED tester, which is not available? What voltage is needed to light the individual LED strips to determine if any are bad? I don't have an E lab at my disposal so it needs to be a simple solution. Telling me to use a "wallwort" won't get it as I don't know what one is in the USA ;-)

2. Is there a VOM (or other) method of testing the LED strips? If so, what should the readings be at the main plug, or on each strip?

3. Others have posted that they have 66v at +Vout 1 and +Vout 2 pins of the Power/Driver board with the LED supply plug connected or disconnected (as do I). What's the cause? What components are most likely the culprits? I can't locate a schematic or functional diagram of this board anywhere. (Did I just show my age? After all, I am an old discrete component era tech;-) )

I ordered a new PS board and when installed, it had the same issues as the one I removed - 66V vs ~87v on v1out and ~128v on v2out from the output of the LED driver section. The supplier is going to replace it but I'm concerned I could get another bad one or my LEDs might be blowing the good board's output section. (I intend to leave the LED cable disconnected and measure the output of the next board FIRST).

Am I over-thinking this problem? Any knowledgeable response would be appreciated. Most strings on these issues just die with no posted resolution.

Regards,
/herb

Last edited by HGSR; 03-16-2017 at 12:17 PM..
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Old 03-16-2017, 01:36 PM   #2
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Default Re: Vizio E420i-AO tech help?

First, we need good clear straight shot pictures of your boards.
There are more than one version of you TV, so which are the boards used in your TV? see here:
http://www.shopjimmy.com/catalogsear...?q=Vizio+E420i
Right now we do not know which power supply board you have to go further. We will not be surprised if you have some bad LEDs.


1. How can I test the LED strips of this unit without the slick ShopJimmy.com LED tester, which is not available?
He has 49 in stock:

http://www.shopjimmy.com/sid-gj2c-le...ght-tester.htm
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Old 03-16-2017, 02:47 PM   #3
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Default Re: Vizio E420i-AO tech help?

Well since it's a vizio which is LG the worst models for bad led's about 95% sure you have burned out led's. I bought led tester for $36 on ebay works great. You can also pull panel and with main and powerboard hooked up it will flash your leds and you can see witch are bad.
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Old 03-18-2017, 07:16 AM   #4
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Default Re: Vizio E420i-AO tech help?

Power supply board is 0500-0605-0300. Here's a pic http://www.shopjimmy.com/vizio-0500-...-led-board.htm (This board is interchangeable with 0500-614-0300)

I agree with the bad LEDs assumption. But the PS board is only putting out 66v on +Vout1 and +Vout2, at the connector with the LED supply cable disconnected. Shop Jimmy's video on testing this specific board (https://youtu.be/W2PFEdrL4lU) says it should be putting out something like ~87v on v1 and ~128v on v2 with the LED cable disconnected. The board they sent me has the same bad readings. They are sending another PS board.

Thanks for the tip on firing up the LEDS with the panel removed. That's my next test once I get good power to the LEDS. I'll also look on EBay for an LED strip tester.

Sure would like to know what components are associated with the LED supply voltages on this board. Since the output is identical on both pins with the LEDs disconnected from the board, seems suspicious that an LED is at fault. Would like to do some troubleshooting on this board. Hate just throwing parts at this thing, especially when a replacement acts the same as the bad one with the same bad readings. I may just be paranoid and received a bad replacement board. That 66v number pops up in other strings on this board and now I have 2 doing the same thing. Would like to solve that mystery. Caps and diodes are cheaper than entire boards.
Thanks
/herb
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Old 03-18-2017, 08:59 AM   #5
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Default Re: Vizio E420i-AO tech help?

Well if you want to repair board Budm is the one who can help you. I like to repair at component level so would be interested to find out problem.
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Old 03-18-2017, 12:45 PM   #6
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Default Re: Vizio E420i-AO tech help?

Roger that.
It just seems that the PS should first be functioning at the proper voltages without a load before looking for additional issues. But I agree the LEDs need to be looked at.
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Old 03-18-2017, 04:29 PM   #7
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Default Re: Vizio E420i-AO tech help?

pics?
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Old 03-22-2017, 07:14 AM   #8
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Default Re: Vizio E420i-AO tech help?

Just to recap: Sound, no backlight on this set. Flashlight test shows full picture.

Will try to post pics of board. Replaced 0500-0605-0300 PS BD twice, still only 66v on LED driver outputs Vout1 and Vout2 with the LED cable disconnected from the board so I have to believe it's not a LED PS problem. The chance of 3 PS bds all having the same issue resulting in the same output voltages are slim.

I have all the correct voltages on the logic board cable including BL on/off at 3.2v. The only voltages in question are on pins 10 and 11 labeled PWM1 and PWM2 respectively. Not sure what they should be. Again, have put 3 different 0500-0605-0300 PS boards in this set, original plus 2, and no change in LED PS output. So I'm moving on the LOGIC board as possible source of issue. Also, I'm not sure there isn't a bad setting, I.E. Backlight set to MINIMUM, but I have no way to tell. Another Logic board should eliminate that possibility as hopefully the settings will have been left at "normal".
Will try to post pics.
Frustrating.
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Old 03-22-2017, 07:22 AM   #9
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Default Re: Vizio E420i-AO tech help?

I up loaded pics. Again, 3 boards, same 66v on the 2 LED outputs. Prob not a PS issue.
Attached Images
File Type: jpg IMG_0432.jpg (444.5 KB, 12 views)
File Type: jpg IMG_1430.jpg (555.3 KB, 15 views)
File Type: jpg IMG_1431.jpg (688.8 KB, 11 views)

Last edited by HGSR; 03-22-2017 at 07:24 AM..
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Old 03-22-2017, 08:09 AM   #10
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Default Re: Vizio E420i-AO tech help?

What voltage do you have at B/L ON/OFF?
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Old 03-23-2017, 06:30 AM   #11
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Default Re: Vizio E420i-AO tech help?

Quote:
Originally Posted by dick_barton View Post
What voltage do you have at B/L ON/OFF?
3.2v
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Old 03-23-2017, 08:51 AM   #12
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Default Re: Vizio E420i-AO tech help?

You say you have all the output DC voltages and also the Backlight On voltage, however the Led voltages are low at 66V and not showing the 80V & 120V as shown in the shopjimmy video.

This would lead me to believe that you may well have a LED boost voltage problem on the power supply board.

Can you supply a picture of the underside of the power supply board especially the led driver IC and give its part number.

Edit
Is there a burn mark on the transformer?
Attached Images
File Type: jpg IMG_1431.jpg (1.22 MB, 15 views)

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Old 03-23-2017, 09:55 AM   #13
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Default Re: Vizio E420i-AO tech help?

I think what he needs to do is to put black probe on the chassis, red probe on the LED+ one at a time THEN turn on the TV to see if the Voltage jumps up higher than 66V or not and then settle down to 66V..
You have two boost converter circuits for two set of LED strings.

Last edited by budm; 03-23-2017 at 09:56 AM..
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Old 03-26-2017, 11:34 AM   #14
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Default Re: Vizio E420i-AO tech help?

Quote:
Originally Posted by budm View Post
I think what he needs to do is to put black probe on the chassis, red probe on the LED+ one at a time THEN turn on the TV to see if the Voltage jumps up higher than 66V or not and then settle down to 66V..
You have two boost converter circuits for two set of LED strings.
Bud,
Yes, that's exactly what they did on all three PS boards, the original plus 2 from shopJimmy. So suspected it wasn't caused by the PS boards. I just put another logic board in and got the same result - sound, picture but no backlight. Outputs on +Vout1 and +Vout2 settled after initial power-up to 66v.

But now I've screwed myself. As I was checking and comparing voltages on the PS board must have pissed something off and got a loud crack and everything silent. Checking voltages on the ins of the logic cable to the PS board, I'm. Now missing the 12v. So I'll get yet another PS board (sent the other ones back to ShopJimmy). Then we can re-visit this whole issue if the new PS BD doesn't solve the issues.

THanks guys!! I'll get back to you soon.
/herb

Last edited by HGSR; 03-26-2017 at 11:42 AM..
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Old 03-26-2017, 11:41 AM   #15
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Default Re: Vizio E420i-AO tech help?

Dick,
Got a snag (see post above). Will return to this string when I get another PS BD. Then I'll let you know where we are with the 66v issue. It's definitely NOT the logic board (changed it) unless I have another bad one.

There have been 3 PS bds in the machine all with 66v on the LED driver cable pins with the LED cable disconnected or connected. Go figure.
/herb
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Old 03-26-2017, 12:10 PM   #16
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Default Re: Vizio E420i-AO tech help?

Just so everyone that is generous enough to help me knows, I've put a $100 budget on this repair. So far I've not spent $25, and that's been on postage to return 2 PS bds ShopJimmy.
My time is not of value as I am retired and needed a project ;-) I was an ET many years ago and I'm enjoying this effort. I am frustrated with no schematic or o'scope like the old days. But you guys are showing me it's possible to actually do this without them.

I've just ordered another PS BD since I"m pretty sure I've blown something else this one while checking voltages. I may even order a "repair kit" from ShopJimmy. They have one for this board for $19.

I appreciate everyone's time and advice.
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Old 03-30-2017, 03:18 PM   #17
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Default Re: Vizio E420i-AO tech help?

Quote:
Originally Posted by budm View Post
I think what he needs to do is to put black probe on the chassis, red probe on the LED+ one at a time THEN turn on the TV to see if the Voltage jumps up higher than 66V or not and then settle down to 66V..
You have two boost converter circuits for two set of LED strings.
OK Folks, we're back in problem mode again. I replaced the PS BD that I fried with a probe slip, and this board measures EXACTLY the same as the other 3 did. There is no backlighting. I have sound, a picture (seen with a flashlight) and all other functions that I can tell with no backlight. I have replaced the LOGIC board and the symptom does not change. When the unit powers on, the voltage on Vout1 and Vout2 of the LED connector goes to 128v and decreases to 67.1v and holds there - with the LED cable connected or not. In fact, with the latest PS bd, I left the LED cable disconnected and measured the voltage before connecting it (after power-down, then up again). It's as if the BL is turned off. But with a different Logic bd and PS bd, this shouldn't be the case. Also, both LED arrays would need to be OPEN for them to cause the same reading as a disconnected cable - highly unlikely.

So I'm suspecting something else. Does the Tconn bd have any influence on the backlight?
Here's the pin readings on the PS to LOGIC cable -
Pin. Function. V Reading
1 and 2 SBv. 5.15
3-5. Grnd
6. 12v. 11.9
7. 12v. 11.9
8. Remote on/off. 3.2
9. BL on/off. 3.2
10. PWM1. 3.2
11. PWM2. 3.2
12. N/C. 0
These all seem normal per the ShopJimmy video on this exact board and model TV.
Anybody have any idea how to make the backlights come on?
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Old 03-30-2017, 04:00 PM   #18
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Default Re: Vizio E420i-AO tech help?

The fact that the led boost voltages initially rises high before falling back to 66V would be indicative of open circuit led(s).
"Highly unlikely......" no it isn't unfortunately. It could also be a fault between the strip connections of which there have been lots of threads about this sort of problem.

Last edited by dick_barton; 03-30-2017 at 04:02 PM..
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Old 03-30-2017, 05:33 PM   #19
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Default 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.

Last edited by HGSR; 03-30-2017 at 05:39 PM..
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Old 03-30-2017, 07:31 PM   #20
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Default 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.

Last edited by budm; 03-30-2017 at 07:32 PM..
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