Vizio D500-Bi No Backlight - Sorta

[keithsipa]

Hey all,

I am by no means an electronics technician, but more of a jack of all trades. That being said, I am looking for some experts in the field to help me out with what I should be doing next to troubleshoot.
I have a Vizio D500-Bi that if unplugged or not turned on for a while (1 hour perhaps) it will start and work fine, until it is turned off.

Once the TV is shut off, it will not turn on again, however the stand-by light will light up and there is 5v at the stand-by pin on the power supply. If I try to turn it on immediately there is no sigh of life at all, other than the the standby light illuminating.

If I unplug the TV for 10 or 20 minutes. Then try to power it on, the big V will appear for a very short amount of time on the screen, then the screen will go black. There is no blacklight, and when I try the flash light test, there does not appear to be any image on the screen.

If I leave the TV unplugged for a while (around an hour or longer) the TV will turn on and work as normal. Then the same thing happens again, if I turn it off.

I have disassembled and looked at the power supply and main board and there are no obvious signs of any problems on any of the boards.

What are the first steps to take. When I had the back off of the TV, I had probed the voltages at the power supply to the mainboard, the standby voltages were a steady 5v, pins 15 and 16, pins 11-14 seemed to be running around 15V while the TV was working fine.


Any help would be appreciated guys.

[budm]

Re: Vizio D500-Bi No Backlight - Sorta

Check PS-ON (command signal from main board) pin when TV is working and when it is not working, <1VDC = main power supply off, >2V = main power supply is turned on.
I would suggest you to read basic troubleshooting guide.

[maxvalutech]

Re: Vizio D500-Bi No Backlight - Sorta

Sounds like a PSU problem (not turning on) and this can be due to itself or to main board not sending turn on voltage signal when warm. Follow budm advice and particularly how main and PSU are supposed to interact together at start up.

[keithsipa]

Re: Vizio D500-Bi No Backlight - Sorta

Will do guys. I appreciate the response.

[keithsipa]

Re: Vizio D500-Bi No Backlight - Sorta

Thanks for the suggestions guys. Went through the basic threads, then found these 2 posts with very similar issues.
https://www.badcaps.net/forum/showthread.php?t=59376
https://www.badcaps.net/forum/showthread.php?t=54991

Did some followup testing when working and not working.
In working condition, here is the power supply pins:


When the TV is in a non working state, here is the pins:


It would appear that it is normal to have 15V on the 24V rail on this set.(at least from the experience of the other posters) However, it would also appear that the problem is in the generation of the 15/24V. I am leaning toward trying a replacement power board.
PS- it appears I got the model wrong in the title if someone can edit.. It should be a B500i-B1

[keithsipa]

Re: Vizio D500-Bi No Backlight - Sorta

Anything else you suggest I check.
The boards for these are not widely available, so I want to be pretty sure.
The only other thing I was thinking was to remove the LED driver cable from the power supply to make sure that something else is not drawing down the voltage.

[CapLeaker]

Re: Vizio D500-Bi No Backlight - Sorta

If you look on your main board top left corner, there is another small power supply there too. A bunch of caps and 2 fets. So unplugging the LED's from the main board won't get the effect desired.
If memory serves me right, a few years ago there was an issue like this on bad caps. I think the back light driver is on that main board, not on the PSU. You have to do more testing for sure to figure out what is causing what here. I think you found the thread already.