Vizio M43-C1 No Backlights

[neilc6]

This is a fairly new 4K TV. When the power button is pressed, the front LED turns on but there is no backlight. I had a cracked screen of this model but sold all the boards. Doh!

Probing the main power supply connector, all voltages look good though 12V is really 19V. PS-On comes on at 3.6V but BL-ON doesn't. Main board is getting power.

Searching the main board on Shopjimmy indicates an EEPROM is available for this model with the symptom no backlights. There is an associated video with a different model but similar main board showing location of U202 (back side of the board). Tried freezing and it didn't turn on. Ordered eeprom from their ebay store since it is free shipping versus their website direct.

[jjanssen7]

Interesting. Let us know what you find out!

[neilc6]

EEPROM didn't work. Luckily, used main boards are only $30 so only an extra $15 gamble.

[jjanssen7]

still following....

[neilc6]

Board came in and TV is working. Shoutout to Electroparts online. They have free returns as well just in case. Since this is a 4K TV, I'm going to trial keeping it as a 4K monitor. It's like 4 x 22" screens tiled.

[jjanssen7]

Interesting. part of the reason I was curious was because I've come across the M50-C1 with similar problems in the past. I'll look a little closer at the main board next time.

[neilc6]

The working board had leds lit up on it that weren't on the non working one. Possibly bad regulators or shorted caps.

[jjanssen7]

I can look for that with the 50" version too.

[howardc64]

Have a M43-C1 with similar failure as neilc6

- No backlight, no LCD image via flash light test, no sound.

- Plug in power cord, main board LED turns to purple for few seconds then to red (looks like standby)

- Press power switch, main board LED turns from red to purple. Front Lower left TV power indicator turns on white and fades away soon after

- About a minute later. TV power indicator LED will blink once, followed by 27 blinks. Then main board LED turns red

- About 30s later, main board LED turns purple, TV power indicator LED blinks 25 times (last blink truncated). Then main board LED turns red. Then cycles this pattern every 30s or so. Sometimes blinks 24 times, sometimes 25 with last blink truncated. Seems to vary.

- When powered on, PSU connector to main board reads PS_ON = 3.68, 5V = 5.1V, 12V = 18.9V, BL_ON = 0.2V

Also disconnected the 2 T-Con board's drivers connection individually to make sure no fault in the panel (read that somewhere) no difference.

Sounds like a bad main board and its internal components? I've got the main board out, removed the rubber pads, still need to remove the black heat sink and the thermal contact pads underneath before can reflow. I have a really thin flux used to reflow XBOX360 GPU. I've used it on Macbook Pro GPU BGA (prone to heat related BGA ball failure) followed by heat gun reflow that worked. Perhaps I can give reflow a shot on the BGA. Lots of GPU fixes also done by reflow by oven but I'd rather do localized heating for now rather than baking the t-con board connector. I realize this method of BGA reflow may not last.

Anything else I should diagnose before going ahead with reflow or main board replacement?

[howardc64]

Found Nick's post on a fairly similar main board to heat the heat sink for 45s.

https://www.badcaps.net/forum/showthread.php?t=77206

post #1 has the board pic (matches pretty close to my m43-c1 main board, see attached pic in this post), #4 is Nick's suggestion, #5 is reported success. Did it a couple of times without success other than blinking lights now blinks 15x (Seen that before earlier).

I guess next step is to remove the black heat sink and the thermal contact pads underneath and heat gun reflow again.

[nomoresonys]

Could be bad micro, if so need replacement mainboard, 3 on this page, make sure you match up the top numbers and letters on the white sticker yours looks to be XFCB0QK0030: https://www.ebay.com/sch/i.html?_fro...acat=0&_sop=15

[nomoresonys]

Looks like Neilc6 had similar issue bl-on too low or 0.

[diif]

Originally Posted by howardc64

H
- When powered on, PSU connector to main board reads PS_ON = 3.68, 5V = 5.1V, 12V = 18.9V, BL_ON = 0.2V

Is that right ?

[neilc6]

Yeah I measured 19V on the pin marked 12V as indicated in first post and BL-ON not coming on.

[howardc64]

thx nomoresonys and neil6 for the quick responses. Will report back after remove heat sink+reflow. If works, then will be confirmation replacement main board would fix the issue if decide to get a replacement board.

On sourcing main board, board prices have gone up since neilc6's $30 just 2 months ago and other variations are cheaper. I'm assuming best to match part number exactly? (XFCB0QK003020Q on my board) I guess BGA heat related failures = demand greater than supply haha. Do these main boards have differing communication protocols to other boards (such as TCON which probably have the most complex protocol compared to other boards) depending on part number?

Last a question on cooling, heat sink size and BGA failure rate suggest inadequate BGA cooling. Think squeezing in a fan would help a lot? Have a spare Macbooks fan and Apple runs them constantly at 2000RPM minimum which is very silent. Also laptop class heat pipes might do a better job than current heat sink whisking the heat from BGA to a fan. In any case, tight fitting for a thin fan but probably can fit it between main board + LED driver board near the main board's PSU connection.

[nomoresonys]

I think fans can be a good idea, lots of people say they never had a problem after fixing and installing a fan, have also seen lots of fan mods on youtube and here on this forum. I think I would definitely use a fan if I did a successful diy reflow, should make the fix last longer.

[neilc6]

For bga issues, heating the processor with a hair dryer is one way to confirm it. Would wrap a laptop in a blanket heating it up to get it to boot and it would work pretty consistently.

[nomoresonys]

Originally Posted by neilc6

For bga issues, heating the processor with a hair dryer is one way to confirm it. Would wrap a laptop in a blanket heating it up to get it to boot and it would work pretty consistently.

+10 Great idea.

[howardc64]

Originally Posted by neilc6

For bga issues, heating the processor with a hair dryer is one way to confirm it. Would wrap a laptop in a blanket heating it up to get it to boot and it would work pretty consistently.

Ah yes, forgot about the blanket reflow trick

Unfortunately reflowing the BGA not working for me. Tried a few heat cycles (didn't remove cumbersome heat sink, heat gun with high low setting and used both, didn't dare to go crazy, always moving side to side and up and down (1" to 3-4" from surface), both sides, when surface mounts solder gets a little shinier, stop/move, never more than 45s on a side) Behavior is same after each heat cycle (no backlight, no image, no sound, all voltages same as before) except blinking lights seems to be reliably at 14-15 now rather than 24/25 as before.

Still looks pretty definitive main board failure (BL_ON=0.2V, all other rails as expected) no sound. Will be sourcing that and report back after install.

[diif]

Originally Posted by howardc64

Ah yes, forgot about the blanket reflow trick

Still looks pretty definitive main board failure (BL_ON=0.2V, all other rails as expected) no sound. Will be sourcing that and report back after install.

Is your 12v rail still 18.9V ?