e701i-a3 no picture but backlights

[Blessed]

Re: e701i-a3 no picture but backlights

Thinking about it.. Could I desolder something off the original bad board and use it on the new bad board.. I do have one good board left

[budwich]

Re: e701i-a3 no picture but backlights

if you are thinking about soldering, then you are almost probably going towards fixing the boards outright. You likely only need a small "transistor" that is most likely blown. If you scan thru the thread you can find where to order a "bunch" for a "few dollars". Anyways, don't start "tearing off ribbons" until you are able to do better testing. IF you already burnt one card with one test, you can gamble with the other and do a "quick test" with the other side disconnected at the tcon and go from there.

Further note: you can test a card to see if the "transistor" is blown or if you other issues using a meter. again read thru the thread to look for some of the resistance checks that people do.

[Blessed]

Re: e701i-a3 no picture but backlights

Well.. I read back in a previous post in here that someone used a transistor that was from a diffrent board to get the same desired effect. Is there another transister on the Tcon board currently that I could rip off a bad board1 and put it on badboard2 to use that to test. When I test what am I looking for.. as I saw white on one side and black on the other .

[budwich]

Re: e701i-a3 no picture but backlights

that was because that person likely had other issues with the card and just moved the appropriate transistor over to what they considered a working card except for the transistor... there are other failure possibilities. I think most people in the states have "easy access" to supplies of the component.

as for what you are looking for... something on the screen. :-)
still further, disconnecting cables at the tcon isn't necessarily the best test. There are corners cables at the bottom of each corner of the set connecting the bottom edge boards to the side edge boards. That is the best point to disconnect... why because, if you are successful with your "guess", you will likely see a full display. IF not, the whole screen may briefly light up and then go black as the transistor dies. Hence the "quickness" of making the "unplug" decision. :-) Personally, if it was my "free set", I would track down a supply of transistors and do some "good testing" (blowing a couple of components if necessary) to ensure that I got the right side.

[Blessed]

Re: e701i-a3 no picture but backlights

If there was a like button id give it to ya. Yeah I will.. Thers a mom and pop shop here that carries them. Im gonna go out and gnab a bunch and start burning them out. Thanks for the tip.. Ill do that and report back here.

[montana16]

Re: e701i-a3 no picture but backlights

Back again.
I am the one who had a E701i-A3 that, after replacing transistor on TCON board and peeling back left side ribbon, I still had a horizontal line about 20% of the screen(top) was messed up a couple weeks ago (post 748 and 753 of this thread) Rest of picture was fine.

Anyway, I was cleaning up my shop yesterday and the side boards that I peeled off were on the floor under my bench. I was picking them up to toss and noticed the ribbons that I peeled off did not come completely off. They tore off. Not sure why I didn't notice when I did it but I suspect wife needed something done right at that moment. There are pieces of ribbon cable still attached to the lcd panel! Not sure how much but I disassembled as far as I did before but I cannot get to the panel itself without totally disassembling everything and then still don't know if I will get to it.

2 questions:

1) Is it a possibility that a remaining piece of that ribbon cable could be causing the issue I have? I doubt it cause that line was right there from the get go.
2) Anyone know how to get to the lcd to get these pieces of ribbon cable off?

[budwich]

Re: e701i-a3 no picture but backlights

I think it is likely that there is still some ribbon left on the contact point. Not sure why you need totally disassemble the panel... basically you need to take off the bezel to look at the contact points. You can readily compare the 5 "contact areas" and see if there is differences... especially in and around the one in question. You need to be careful as there isn't much space between track lines. hopefully, some alcohol and light carefully cleaning will get any remaining ribbon material... if this is indeed the problem. clean in the direction of the track... might try plastic razor blades.

[CactusCat]

Re: e701i-a3 no picture but backlights

Just wanted to take a moment and thank you guys for the info provided here. I was given one of the Vizio E701i-A3s as the previous owner had not been able to get it working even after the "repairman" put in all new boards. I ordered 10 of the transistors off ebay to get it work. Just like montana16's experience, my first transistor was either bad or my soldering was not so hot. However, after installing transistor #2, I got voltage on both sides and was good to go. Following the tips and instructions here, I found that my left side (from the front view) was the culprit. I removed the offending connector tabs and the picture is back 100%. I'm not an electrician or a component level repairman, but I do IT support for a living so was somewhat familiar with the small electrical components. My soldering station has a very tiny sharp tip available for it and I was able to do the soldering with the naked eye. My appreciation to all who've contributed here.
CC

[ToxicGumbo]

Re: e701i-a3 no picture but backlights

After reading this entire thread, there hasn't been any talk about the transistor's role. Is this MOSFET being used solely as a switch? Can the transistor be entirely eliminated in this circuit and the source and drain jumped with a fuse? As nutty as that sounds, I'm hoping to generate conversation on repair alternatives.

(And with that, I'm off to place an order for MOSFETs to repair two T-con boards.)

[budwich]

Re: e701i-a3 no picture but backlights

and how would you switch "ON" the fuse? :-) Hopefully, your repairs will be more successful than your "re-design effort"... :-)

[ToxicGumbo]

Re: e701i-a3 no picture but backlights

Easy, now. I'm doing everything by the books and respect all the contributions you've made to help people get there. What I was suggesting is just a poser for conversation. Has anyone investigated the role this transistor plays in the circuit? What's calling it and when?

[tom66]

Re: e701i-a3 no picture but backlights

It's probably part of the boost converter; shorting it is likely to just blow the fuse and break things.

General rule: components are there for a reason , manufacturers rarely like throwing away money.

[ToxicGumbo]

Re: e701i-a3 no picture but backlights

Progress with my TV. Had to wait about a week for five RTR020N05TL MOSFETs to arrive from Mouser. Shipping doubled the price to about $11 total.

The guy I bought the Vizio from (for $100) had two T-con boards in different states of disrepair, the replacement in worse shape than the original. I replaced the MOSFET on both, but only his original board tested to have the expected voltages.

I removed the flat cable from lower right corner (behind the Vizio insignia when viewed from the front) and the LCD continued to display just the blank backlight I had become familiar with. I then unplugged the left corner, reconnected the right, and revealed the image shown in the attached photo. Power cycled at each step of course.

I only read one comment on here about damaging a cable and without details. Of note, these ribbon cables are very fragile. If the ends tap against the sockets they go into, it's easy for the metal traces to rip off and bend. I was lucky that they mostly retained their shape and a small piece of Scotch tape was enough to hold them in place for reseating (as seen in photo 2). Kind of surprised it wasn't a total loss. The other cable did the same thing, but is suddenly less of an issue given the upcoming driver-tab removal. In short, be very careful with your ribbon cables.

[ToxicGumbo]

Re: e701i-a3 no picture but backlights

Pretty uneventful tab-ripping ceremony (thankfully). The TV looks sharp and the wife's happy. An eBay remote clone's on its way in the mail. Thanks, all, for keeping this thread packed full of information and success stories.

First photo: Testing the TV after pulling the tabs
Second: Leftovers
Third: The 70in Vizio in front of a 50in Panasonic plasma TV (a previous repair job)

[Nightrider0614]

Re: e701i-a3 no picture but backlights

Working on one of these bad boys, no picture, did the flashlight test and nothing was there.

Replaced the tcon removing the right hand side connector, no v or anything. So I plugged it back and tried the left side, same thing, nothing.

2 tcons in, 1 new and 1 used. the transistors dont seem shorted and the the fuse is fine.

Replaced the lvds cables going to the main board, could I have a power supply problem going to the main board, hoping to scope out the cables but this thing is so big I'm working on the garage floor. lol

Any tips for me please?

Thanks,
Jeff

[ToxicGumbo]

Re: e701i-a3 no picture but backlights

no picture, did the flashlight test and nothing was there.

One question: When you say the above, do you mean that you're not even seeing the backlight? Does the LCD panel stay dark the entire time as if the TV hasn't even been powered on?

If so, the initial concern is less about the t-con board and more about the LED backlighting or power supply that drives it. It should emit a bluish glow even if the t-con board isn't wired up.


Edit: Okay, technically that was two questions.

[tvsteve2]

Re: e701i-a3 no picture but backlights

I am in the middle of this repair and keep getting confused as to Right vs Left could you specify the side with the tact switches or not?? PLEASE

[ToxicGumbo]

Re: e701i-a3 no picture but backlights

In the very first post, freakaftr8 declared the "right side" of the LCD panel as the side opposite the tact buttons (menu, input, vol, etc.) and the first corner with the ribbon cable to disconnect being on that same side and behind the printed Vizio name (as seen on the bezel's lower right when viewed from the front). Most people have been referring to it the same way, though there's certainly been a lot of "right" and "left" thrown around based on point-of-view and TV orientation, especially since "right" becomes "left" when viewing the rear of the TV.

Ultimately, you can start with either side to disconnect the corner cable, but most seem to have had problems with the side behind the Vizio name, or "right" side when viewing it from the front.

[Nightrider0614]

Re: e701i-a3 no picture but backlights

Thanks for the reply Toxic,
I have backlight and sound, no display.

I have to take a vm to the tcon and see if I got bad tcon boards, also ordered some transistors just in case.

Thanks,
Jeff

[ToxicGumbo]

Re: e701i-a3 no picture but backlights

Someone correct me if these numbers are off, but I would expect to see voltages fairly close to the following (based on previous posts and my own findings, but don't be surprised if yours aren't an identical match even when working):

Silver capacitor: 12-15 V

3R3: 3.3 V
100: 12-13 V
4R7: 1-2 V

MOSFET: (I didn't double check my own readings on this one)
Drain: 15.5 V
Gate: 3.5 V
Source: 0 V

I would only test these with the t-con PCB screwed in place (with at least two screws if not all four), with only the LVDS cables plugged in, not the cables leading out to the panel, and TV on. The screw posts for the t-con PCB are a good place to ground your black lead.

On my t-con, the 3R3, 4R7, and capacitor were all flatlined at 0 V until I replaced the MOSFET.