Vizio M70-C3 diagnosis

[howardc64]

Re: Vizio M70-C3 diagnosis

I did try hot air but without removing the heatsink. Will the studs pop out without pulling the board? Otherwise, sounds like a main board issue, yeah?

Need to becareful heating the main. Proper process is bake to remove moisture to avoid micro expansion popping the chip/board, preheater under the board to avoid warp and crack. I used heat gun on cold garage floor on my first one. Heard a pop at each BGA and main was dead for good. So I've used oven bake method since as it's safer. But that has its own problems (over heat everything for longer than it should)

Furthermore proper reflow repair diminishes as poor man's reflow causes more damage. Since poor man reflow don't last. The only purpose is to confirm the failure but do so without causing more damage.

Was trying to verify the powerboard, but I thing Howardc64 is on the money, probably need a new chip or reworked with leaded balls.

Would be good to confirm not power board. What's the process? Will backlight come on with main disconnected? Or have to jump PS_ON somehow?

[howardc64]

Re: Vizio M70-C3 diagnosis

Nicks tv actually has quite a few YouTube videos on this tv

https://youtu.be/un7OJLTWtJY
https://youtu.be/Q8blOTQKBU4
https://youtu.be/G1Rh6Snf94g
https://youtu.be/IkFCE42zoLM

https://www.nickstvs.com/store/p3008/Y8386674S.html

Probably worth a reach out to confirm your symptoms with Nick before sending in main for repair. He mentions lightning strikes taking out main’s ports in the PSU video. Might ask if he can repair that in case it’s your issue.

[nomoresonys]

Re: Vizio M70-C3 diagnosis

Need to becareful heating the main. Proper process is bake to remove moisture to avoid micro expansion popping the chip/board, preheater under the board to avoid warp and crack. I used heat gun on cold garage floor on my first one. Heard a pop at each BGA and main was dead for good. So I’ve used oven bake method since as it’s safer. But that has its own problems (over heat everything for longer than it should)

Furthermore proper reflow repair diminishes as poor man’s reflow causes more damage. Since poor man reflow don’t last. The only purpose is to confirm the failure but do so without causing more damage.



Would be good to confirm not power board. What’s the process? Will backlight come on with main disconnected? Or have to jump PS_ON somehow?

Not exactly sure on this one, but I think it would involve using resistors to jump from 12vs to ps-on and one or more of the tcon on pins on CN201.

[objext]

Re: Vizio M70-C3 diagnosis

Nicks tv actually has quite a few YouTube videos on this tv

https://youtu.be/un7OJLTWtJY
https://youtu.be/Q8blOTQKBU4
https://youtu.be/G1Rh6Snf94g
https://youtu.be/IkFCE42zoLM

https://www.nickstvs.com/store/p3008/Y8386674S.html

Probably worth a reach out to confirm your symptoms with Nick before sending in main for repair. He mentions lightning strikes taking out main's ports in the PSU video. Might ask if he can repair that in case it's your issue.

Thanks, I had watched those related videos but none touch exactly on the case where I get standby power and turn-on, etc, but no video. I would not be surprised if a surge took out the main board. I replaced the mainboard in my in-law's TV twice after electrical storms. A lightning surge took out the hdmi ports so I replaced the board, and then a second storm rolled through and took it out again less than a week later. Finally got it on surge protection and no problems since.

[nomoresonys]

Re: Vizio M70-C3 diagnosis

Isn't that your symptom, standby light pops on, no picture? he mentions that about 5 seconds in and again at 1:13 in the first video of post #22.

[Donny2derby]

Re: Vizio M70-C3 diagnosis

I'm trying to learn and figure out for myself what a lot of the acronyms are without asking what are annoyingly simple questions for the rest of you but BGA is stumping me. Anyone care to offer an explanation?

Is there a thread with a glossary of common terms and acronyms?

[objext]

Re: Vizio M70-C3 diagnosis

I'm trying to learn and figure out for myself what a lot of the acronyms are without asking what are annoyingly simple questions for the rest of you but BGA is stumping me. Anyone care to offer an explanation?

Is there a thread with a glossary of common terms and acronyms?

BGA is ball grid array. Instead of pins, the chip uses an array of solder balls to make connection to an array or flat solder pads on the circuit board. Basically a surface mount chip solder sandwich. Heat, flex, and lead free solder can lead to the balls cracking

[howardc64]

Re: Vizio M70-C3 diagnosis

I'm trying to learn and figure out for myself what a lot of the acronyms are without asking what are annoyingly simple questions for the rest of you but BGA is stumping me. Anyone care to offer an explanation?

Here is a quick summary overview of this problematic area

~2000 switched to lead-free solder. Unfortunately lead-free solder cracks easier under vibration and thermal stress. For home electronics, big hot BGAs like GPU suffered failures. For automotive, vibration killed a lot of circuit boards. NASA only send leaded solder electronics to space

BGA (Ball Grid Array) is a "chip package" with grid of solder balls (lead free) under it. The actual chip is the silver rectangle on top and is attached to the larger rectangle that is the hchip package which routes chip connections to the grid of balls to solder onto the board.

BGA was invented to handle hundreds to beyond a thousand solder connections to the board. Before BGA was QFP/QFN (Quad Flat Package/No-lead) where connections are on the 4 sides of a rectangular chip package.

Since BGAs include many hundreds of connections, the chip naturally contains lots of functions which runs hotter. GPUs are the biggest examples. Hot running BGA means the chip package is constantly thermal flexing and end up cracking the solder balls.

Once solder ball is cracked, the cracked surface oxidizes, re-melting doesn't provide longevity as the oxidized surface is still present and will likely crack again in not too disantt future with more thermal cycling.

https://www.semanticscholar.org/pape...ed6fd/figure/1

Anyway ~2015 Vizios were particularly prone to this problem. Smart TV + 4K packed in a lot of functions into the BGA chips. Value brand TV BGAs also have to use cheaper older chip factory that makes hotter running chips. LCD TVs also basically all skip fans to help remove the heat away from the heat sink.

[Donny2derby]

Re: Vizio M70-C3 diagnosis

Thanks very much to both of you. Very enlightening. Sounds like a common occurrence across many types of PCB with a never ending list of issues it could cause and certainly not the easiest to repair.

Time for some YouTube videos on the subject!

[objext]

Re: Vizio M70-C3 diagnosis

Going to try out a "tested" mainboard from ebay. I'll report back when I get it and swap it in.

[objext]

Re: Vizio M70-C3 diagnosis

Finally got around to trying the ebay board. TV is working with the replacement main board. Going to pull the heatsink and replace the thermal compound before I button everything back up.

[gladiator1]

Re: Vizio M70-C3 diagnosis

Finally got around to trying the ebay board. TV is working with the replacement main board. Going to pull the heatsink and replace the thermal compound before I button everything back up.

@objext: That's great. I have the same problem as yours. Can you point me to which eBay board did you buy? Separately, are you going to pull the heatsink from your old TV and put it on the new board?

[objext]

Re: Vizio M70-C3 diagnosis

@objext: That's great. I have the same problem as yours. Can you point me to which eBay board did you buy? Separately, are you going to pull the heatsink from your old TV and put it on the new board?

The seller only had the one board...looked like he was parting out one TV.

Here's the one I bought and the one I replaced. The seller included the heatsink & heat pipe with the board. I just meant that I will take it off and replace the thermal compound & reinstall since it's likely old & dry and I have quality thermal compound on hand.

[objext]

Re: Vizio M70-C3 diagnosis

Well, kind of a kick in the balls. I hadn't given the screen a good look after changing the main board, and I had never seen this TV working prior do the board going out. Looks like it also has some half failed LED strips. I swapped some of the backlight power ribbon cables around and the dim spots remained in the same locations so I think it's just the LEDs and the driver is fine.

On the fence as to whether fixing it at this point is worth it or not.