Vizio P502ui-B1E power light turns on, but no picture

[nsab6464]

Hey guys,
I have a Vizio P502ui-B1E with no display activity at all with the power light on. It broke in a very specific way, and now exhibits strange behavior when turned on (slow response to power off command, restarts every 90 sec, more below), so I'm hoping that someone with experience working on this TV can point me in the right direction.

I already tried the 2 most common fixes with no luck:
- Replacing the T-Con board.
- Re-flashing the firmware on the U202 chip (from here: https://www.badcaps.net/forum/showthread.php?p=840012)

Here's exactly how the TV broke:
About an hour into watching a show in 4K resolution, the right half of the picture turned into colorful pink-ish noise (at the pixel level). The left half of the picture was completely normal and the TV was responding to remote control input normally. The picture corruption affected all inputs and even the on-screen-display menus drawn by the TV itself. After about 30 seconds, I turned the TV off with the remote control, in an attempt to reset it. It turned off normally. It would not properly turn on again.

Here's the current state of the TV (starting with plugging in the power cord):
Less than a second after the power cord is plugged in, power is applied to the USB port for about a second. Less than a second later, power is applied to the USB port again, also for about a second, and, at the same time, the white power light (bottom-left of the TV) turns on bright. A few seconds later, the power light starts slowly dimming and soon turns off. TV is now in standby. This startup sequence is normal, as far as I know.

When the power button is pressed on the back (or the remote), the power light immediately turns on bright. Less than a second later, a 1-second burst of power is applied to the USB port. Less than a second later, power starts being applied to the USB port continuously. This sequence is also normal up to this point.

At this point, the screen would normally turn on and show the Vizio logo, but the screen stays dark. The power light dims to low a few seconds later (this part is normal). The TV does not appear to properly respond to inputs at this point - pressing the power button (either on the remote or on the back of the TV) does not turn the TV off immediately. It will only turn off after a random period of about 5-60 seconds. If left in the powered on state, the TV will also reboot exactly every 90 seconds forever (by reboot, I mean the power light turns bright, power disappears from the USB port for a few seconds, then the sequence of events restarts as in the previous paragraph). During this sequence, the bottom processor on the main board (MIPS) generates plenty of heat while the top one (FRCX) only generates a little.

Interestingly, the TV behaves the in the exact same way (previous 3 paragraphs), no matter what is connected to the main board. If I disconnect all cables (except power input and power button/ir circuit), and even desolder the U202 firmware chip, the TV will behave in the EXACT same way.

So what should I look for next? Both processors have what look like a JTAG and an I2c interface on the main board. Any way to talk to them maybe? Thanks for any ideas!

[Diah]

Re: Vizio P502ui-B1E power light turns on, but no picture

remove all USB pin from set and also disconnect LAN , plug it out from wall socket and keep ir for 2 minute while you press power and channel up on tv panel.. after this 2-3minutes passed release them and keep channel up pressed and plug it to wall socket as solo tv and when it on should make clear flash from SM

[nsab6464]

Re: Vizio P502ui-B1E power light turns on, but no picture

Thank you for your reply, this didn't work unfortunately. Also, this TV does not have a physical channel up button - it only has a power button on the back. So when following your directions, I tried keeping the physical button power pressed as I plugged it into the wall socket, then tried keeping the channel up button pressed on the remote as I plugged it in, then a combination of the two. No luck.

Any other ideas? Thanks in advance.

[Nick's Tvs]

Re: Vizio P502ui-B1E power light turns on, but no picture

Heat up the main heatsink on the main board with hot air. Heat sink is very large, may need to heat up for 45 seconds or so. Let sit for 15 seconds for heat to dissipate into BGA chips and then power on. Should allow the set to come on and temporarily work.
BGA chips are almost always the issue on these main boards.

[nsab6464]

Re: Vizio P502ui-B1E power light turns on, but no picture

Thanks! You nailed it!

Guess I'm gonna have to cook the CPU every now and then...

[Louis82]

Re: Vizio P502ui-B1E power light turns on, but no picture

Hi Nick - Which BGA chip should be replaced, the one on the top close to LVDS connectors or the one close to the tuner?

Thanks in advance

[vestaviascott]

Re: Vizio P502ui-B1E power light turns on, but no picture

Heat up the main heatsink on the main board with hot air. Heat sink is very large, may need to heat up for 45 seconds or so. Let sit for 15 seconds for heat to dissipate into BGA chips and then power on. Should allow the set to come on and temporarily work.
BGA chips are almost always the issue on these main boards.

What method do you guys use for this? Will a heat gun work? Apply heat to the top of the large black plate on top center of the main board? Or apply heat to the underside of the board when removed from the TV?

[Nick's Tvs]

Re: Vizio P502ui-B1E power light turns on, but no picture

In regards to which BGA, we recommend you reflow, reball and or replace both the large BGA chips. If only one is reworked, then the other is most likely to fail soon after.

As for what method for heating to diagnose the issue, we do use a heatgun. We heat up the black heatsink for 30-45 seconds and let the board sit for a bit to absorb the heat. Then we plug the set in and see if the TV turns on properly. If it does not, we repeat the process a second time.
99% of the time these TV sets have cracked joints on the BGA chips, the issue is almost never on the eeprom or other parts of the set as commonly believed.

[howardc64]

Re: Vizio P502ui-B1E power light turns on, but no picture

Thought I share heat gun reflow experience on this board with 2 TVs (M43-C1, D50U-D1, both with this basic main board design)

Tried heating the heat sink on both boards and couldn't get it to work. Probably due to inexperience and I'm guessing need to get it hotter than I was comfortable. Due to the large heat sink, probably a lot hotter than my usual reflowing naked chips.

Removed the heat sink. One board had soldered on heat sink which was difficult. The sink attachment posts were large and had a lot of solder. Also hard to heat up due to the heat sink. Needed a Hakko desoldering gun and a second soldering iron with 2 people. The second board had the later designs with springed plastic studs which were much easier.

First board reflow used some liquid flux (people used for XB360 reflows) to soak under the SOCs. Proceeded to heat to about 250C with a metal temp probe held above the chip. Heard a pop on each chip, board was deader than before. Guess it was too hot and damaged.

2nd board reflow used no liquid flux. Digital laser pointing thermometer. Warmed up the area around the SOC and heated both SOC to 130C. This worked. TV now working and we'll see how long it last. Needed white thermal past (K5 Pro) to reassemble the heat sink.

[nsab6464]

Re: Vizio P502ui-B1E power light turns on, but no picture

I should share my experience as well.

I'm not nearly skilled enough to do a proper reflow, and lack the necessary tools anyway, so I simply used a heatgun to 'cook' the mainboard every time it stopped working (see my OP above for how the TV behaves in that state). I laid the mainboard flat and used a cheap Chicago Electric #69343 heatgun, at the High,970F setting, aimed at the large heatsink right above the north BGA chip, about 1cm away for 60 seconds (note that this is probably too much heat if you have a better heagun!). I then let it rest for at least 60 seconds. Just as Nick's Tvs wrote above, after this, the TV would temporarily work for a while. This process worked without fail and never took more than 2 attempts - and I've now done this close to 50 times!

Obviously, the problem with this method was that it's VERY temporary. The TV would work for only about a week before I had to 'cook' it again - it was VERY annoying. I stopped bothering to properly reattach the board to the back of the TV, and instead just kept it laid flat even during operation, propped up by some CD spindles. I noticed the heatsink would get very hot during prolonged operation (this is normal - bad design on Vizio's part), and had an idea to put a large slow-spinning PC case fan on top of the heatsink and run it off the 5V line of the mainboard so it would turn on/off with the TV. This helped, but not much, the TV would now work for about 2-week spans before failing.

I then put a heavy 12V lead-acid battery (the small kind, not the size used in cars) on top of the heatsink (propped up about 10cm to avoid it heating up) so that it applies heavy pressure on the heatsink. ...The TV has now been working for 4 months

TL;DR: TV is 'fixed' - laid the board flat, 'cooked' it with a heatgun, propped a heavy object on top of the mainboard heatsink so that it applies downward pressure, and put a slow PC case fan directly on top of the heatsink to keep it cool. Ugly but works great!

[nomoresonys]

Re: Vizio P502ui-B1E power light turns on, but no picture

Nice job, proper cooling is the key.

[Nick's Tvs]

Re: Vizio P502ui-B1E power light turns on, but no picture

When it comes to reflowing, a general rule of thumb is to preheat the board at 120 degrees C for a few hours to get rid of any moisture. If you do not do this, then you run the risk of getting that popcorn effect on the board and or also that pop sound that howeardC64 described he had on one of his boards.
This also is a good time to transition into the reflow as you will be starting at a good base temp wise on the board. Another tip is to avoid going above 210 C and to try and stay at those higher temps for no more than 20 seconds.