Vizio E420i-AO tech help?

[HGSR]

Re: Vizio E420i-AO tech help?

Thanks for the quick response Bud. Wow, maybe I haven't lost it completely :-). That's what I was thinking too. I'm going to wait till I receive the LED tester before I crack this thing open. I'm also going to order a set of LED strips for this unit from ShopJimmy. As long as I'm in there I may as well replace them. This unit has a lot of hours on it. Small investment.

Vince, Thanks. I've been watching them for days. That guy Tampatech has some good vids.

Thanks Guys, I'll let everyone know what happens when I open this up next week.
/herb

[budm]

Re: Vizio E420i-AO tech help?

That tester will be a good investment so you do not take a chance of cracking the screen to get to the LEDs, opening up the last screen is the last thing you want to do.

[vinceroger69]

Re: Vizio E420i-AO tech help?

budm a question regarding these backlight testers i have not used one myself as yet as had been using a power soure ie 2 aa batteries but with these testers the lcd will still be attached so you apply power to the led strip connectors then the led strip should light if ok? but a strip can still light with leds blown which you maynot see through the lcd so you monitor the voltage too on the tester and see if higher or lower?

[budm]

Re: Vizio E420i-AO tech help?

You will remove the LED connector from the board then use the tester to test the string. The weak point about using the LED tester is that if the panel only uses ONE LED string, so if it has shorted out a couple LEDs, the string will light up but as far as the TV protection circuit is concerned, the shorted out LEDs can trip the over current and shutdown the circuit, but the Tester does not have that and you will still see the LEDs up on the screen (at this point you do not have the screen apart yet). The spec sheet of the LCD will come in handy.
So if you know how many LEDs there are in the string then you can expect what the Volt meter on the tester will show and match the total LEDs in the string, but if you do not know how many LEDs you have in the string, the Voltage reading may be correct or not correct. I.E. you know you have 10 LED in the strip, but the Volt meter on the tester is showing 24V instead of 30V then you know you have a couple shorted out LED on the string.
So when you get the tester, you should test it on some LED strips that you have, record the Voltage reading as shown on the meter and then simulate shorted out LEDS and see if the meter will show less Voltage or not, I hope it is sensitive enough to show 1 shorted LED.

If the panel uses more than one string then you can do the Voltage comparison reading to see which one has shorted out LED/s., but then again I am seeing some panel that does not use the same quantity of LEDs for each string.

[vinceroger69]

Re: Vizio E420i-AO tech help?

Thanks budm that makes sence as all the videos on line showing these testers in action shows the tv already stripped too the led strips and yes i have some spare strips i can use for testing etc would a amp meter be of use and see current being drawn?

[dskall]

Re: Vizio E420i-AO tech help?

I used mine last night to check led's. One string did not light. The other had several bad led's which you can usually see dark areas. Of course knew it was bad when one string doesn't light. I think it is the next best thing to esr tester since backlights are the new plague now.

[budm]

Re: Vizio E420i-AO tech help?

Thanks budm that makes sence as all the videos on line showing these testers in action shows the tv already stripped too the led strips and yes i have some spare strips i can use for testing etc would a amp meter be of use and see current being drawn?

The Volt meter of the tester is showing the Vf of the LED (1) or the total Vf of the whole string of the LEDs. Since it is constant current power supply, the current will remain the same with shorted LED or without shorted LED.

[vinceroger69]

Re: Vizio E420i-AO tech help?

The Volt meter of the tester is showing the Vf of the LED (1) or the total Vf of the whole string of the LEDs. Since it is constant current power supply, the current will remain the same with shorted LED or without shorted LED.

Thanks budm im still learning so all of this makes sence now once tester arrives i will do some testing on old strips i have and maybe short out some and see what diffrence it does make. I was ok testing leds with multi meter and battery pack but the risk of damaging the screen is always on your mind.

[HGSR]

Re: Vizio E420i-AO tech help?

E420i-AO FIXED!!! Thanks to BUDM even an old dog like me can learn new things. Bud, I owe you an adult beverage if we ever meet!!

I'm posting what I found and did on this "No Backlight but Sound" problem so the next guy that does search on this model can benefit.

Note: As a veteran of other boards on other subjects, I may use more than one reply to post this info. I've ever been bounced in the middle af a lengthy response and had to start all over writing it. So multiple short posts are better.

For those of you that like me, have looked at YouTube vids and read multiple other posts on the issue of "No Backlights but Sound and Video using the flashlight test", or may have seen the ShopJimmy or Tampatec YouTube videos that say if the output of the LED driver board is too low, you have a bad power board, don't always believe it. If you read the previous posts in this string, you will note the output of the LED driver board on my unit was 67v on both LED1+ and LED2+ pins of the connector cable. All info available said this unit should have 100v and 90v respectively on these pins. All the videos out there said if it's low at those pins, the PWR board was bad - WRONG. Thanks to BUDM, the correct trouble shooting method pointed directly to the problem - a BAD LED STRIP on L1.

[HGSR]

Re: Vizio E420i-AO tech help?

Reply cont.
In the previous posts, you will note I had only measured L1+ and L2+ as shown in all videos on this subject. The voltage I found was 67v on both. I assumed something or some setting was clamping the voltage output to 67v vs the 90 and 100 required. Others have posted finding the LED driver voltage at 66v on this model but did not post why or what a resolution to the problem was. Here it is: (this is old news to knowledgeable techs but news to some of us)

As Bud stated, the LED driver section of the PS was in PROTECTION mode due to sensing a bad current draw by the LEDs. It clamped to a 66v or 67v output. This "PROTECTION" mode is never mentioned in most videos on this subject that I could find. At Bud's direction, I monitored the voltages on L1- and L2- during power-up, with the LED cable connected to the board and the negative meter probe attached to the frame of the unit. This pointed directly to the problem. The voltage on L1- never moved off 0v during power-up. However, the voltage on L2- ramped up to 128v then immediately dropped to 67v during power-up. As Bud stated in an earlier post, it appeared there was an open in the L1 string of LEDs. I'm an OLD ET and not current in the field. I would have never thought to monitor the NEGATIVE side of the LED driver circuits assuming it was ground. But since it's one side of a transformer output, it's not ground. Basic stuff for real techs.

After disassembling the screen portion of the unit by following multiple YouTube videos on how to do this, I used one of the LED testers available on eBay for $35 to test each individual LED strip. What I found was one entire strip in the L1 array of 3 strips would strobe when voltage was applied to it. It lit but flashed on and off. All other strips tested fine, lighting as expected when voltage was applied to their test points. What appeared to be an OPEN in the L1 LED array of 3 strips when measured at the connector to the LED driver board was created by one faulty and strobing LED strip in the array. THis put the entire PS in protection mode clamping both the L1 and L2 outputs to 67v even though both LED strips in the 2 strip L2 array tested fine.

[HGSR]

Re: Vizio E420i-AO tech help?

E420i-AO Reply cont. 2
To some newbies like myself, you may note these LED testers state you can test the LEDs "without disassembling" the unit. This is only true if you know what you should be seeing in voltage draws. Before replacing any LED strips, I applied the tester to the + and - pins of L1 and L2 at the cable connector (disconnected from the board of course. The tester showed a 45v draw by the L1 array, and 90v draw by the L2 array. After replacing all the LED strips with "new" set procured of eBay, and re-assembling the unit, I re-ran the same test. I saw 55v draw by L1 and 90v by L2. That didn't tell me much in terms of was L1 bad or not. So some folks may be experienced enough to analyze the LEDs without disassembling the screens and testing each strip individually, but I wasn't. Besides, that strobing strip caused multiple voltage draw indications. Lesson learned, just do it right and go the whole route of opening the unit to test the individual strips if you suspect an issue with the LEDs. Besides, you won't see how many individual LEDs are bad without opening the unit.

Some folks may say, Why waste all this time and effort on a cheap TV? My objective was to try to figure out what was wrong with it. And, what was causing the output of the LED driver circuit to be only 67v. Also, MAYBE fix the unit for under $100. With the generous and patient help of many of you, I (really you) did that. I considered the $100 a reasonable training fee for me, if nothing else. Yes I did swap boards several times with no change to the problem. Those good boards were returned for a $12 restocking fee to ShopJimmy.com (at their suggestion!!). They are great people to do business with. I don't count the purchase of the LED tester as part of the cost since I can always resell it (but probably won't). But the most important part of this exercise is that maybe someone else will benefit from this information. Besides, I saved the cost of having to buy a new TV ;-) I paid $35 for a set of 10 LED strips for this TV and $32 for a PS board I cooked with a probe slip. The rest was eaten in postage etc. Not bad.

Thanks to all of you that helped and old dog learn some new tricks. I have thoroughly enjoyed working with all of you!
/herb

P.S. This TV set had over 10,000 hours of use on it (12hrs/day x 300dys per yr x 3 yrs). They may be cheap but this one earned it's keep.

[budm]

Re: Vizio E420i-AO tech help?

Glad you got it fixed.

[vinceroger69]

Re: Vizio E420i-AO tech help?

Thanks for the update and glad the sets fixed im suprised of the voltage readings with the tester a big diffrence between l1 and l2 and only 10 volts diffrence on the new strip.

[budm]

Re: Vizio E420i-AO tech help?

I forget to ask as to how many LED for each string of the LED1, LED2.

[dskall]

Re: Vizio E420i-AO tech help?

Thanks for feedback. So many leave thread hanging with no resolution, and really just wastes peoples time not knowing what if any suggestion solved the problem.

[HGSR]

Re: Vizio E420i-AO tech help?

I forget to ask as to how many LED for each string of the LED1, LED2.

If I recall correctly,there were 5 rows of 10 LEDs. Each row consisted of two half strips (L1R1, L2R2, then repeated. The other interesting fact is that you could not test the R1 or R2 half strips alone. THey had to be plugged together with their counterpart L1 or L2 halves in order to light up. Then BOTH halves would light up from the tester when injecting voltage at the R1 or R2 test points. Only the L1&2 halves would light up from the tester by themselves. At first I thought I got bad strips but once I recognized the pattern, I was ok with it. Another thing the videos didnn't mention to us newbies.

I can only assume the voltage diff was caused by the fact that L1 drives 3 rows of LEDs while L2 drives only 2. It could also have been operator error. I only did a momentary test not knowing if the tester could handle it. The pattern of strips that could be tested together, positive on one strip and negative on another was also strange but since I didn't change any wiring, I wasn't interested in decoding that. This set has "smart" lighting control depending on the scene and I didn't want to get into that level of analysis. From a newbie's perspective, it was enough that each strip tested good, starting out dim and increasing in intensity after replacing all the old strips with newer ones. I didn't care that they were probably used, they most likely didn't have the hours on them that mine had. Other than that one strobing strip, only one individual LED was bad in the entire set. It's an LG screen. This set runs 12hrs a day 7 days a week. A sane person would not have bothered fixing it.

A not-so-funny story on myself:
After I re-assembled the entire set, and lifted it up to mount the stand on it, I heard what sounded like a screw roll from one side of the set to the other BEHIND the screen. Oh sh_t I said. How'd that happen? So I immediately tore it down again, risking cracking that darned LCD screen to open it up to get the screw out. Turns our it was a lens off one of the old LED strips that popped off when I was stripping them out. I hadn't seen it come off and left it in there. Had I known what it was I would have left it in there!!! Again, another amature move ;-)

[Coast4312]

Re: Vizio E420i-AO tech help?

Im so happy you followed to conclusion. I have the same tv and same read out on led1 and led2 67v. The tv had dark shade in the upper right screen for a few days before the screen went out. I have no backlights but I can see images of the menu when I use a flashlight.
Do I need to have sound? I'm just plugging tv into wall not cable box.
Also what is the model number of the replacment strips. And do you need to replace them all or just the strip that is bad.
I'd like to fix the tv and give it to elderly neighbor who still is using an old tube tv, if I can do it at a reasonable price.
You post helps because I was about to buy a controll board.
Many thanks.

[dskall]

Re: Vizio E420i-AO tech help?

You don't need to replace all strips. Various ways to repair depending on skill level. Replace strip, stacking method, replace individual leds. You can youtube various repair methods.