Vizio E701-A3 Backlight Question

[Tjp444]

This TV would turn on, you could see the Vizio logo for a few seconds and then shut down. Stripped it down, found one led on one strip that was bad, replaced the strip with a used one, now the tv won't start up the backlights.

I tested each of the strips individually with an LED tester, two are at 170v fully lit, the used replacement is at 171v. Is that enough of a difference to stop it from starting?

The power supply starts to ramp up the voltage, seems to get to about 60 and then ramps down with the LED strips connected. Since not all of the pins on PS board are available from the top I'm not sure if I can test across all of the V+ and V- connections. The other voltages on the PS and main board are within spec.

Wondering if there is a reset procedure - I know some TV's after hitting so many attempts at starting the backlights lock up. This is a Sharp TV branded as Vizio.

Any thoughts on next steps? Thanks.

[Tjp444]

Re: Vizio E701-A3 Backlight Question

I have determined there is 3.2V at the "BL ERR" pin, this voltage is present immediately upon pressing the power button. Is this sent from the main board to the PS or is this the PS sending it to the main board? It seems almost too quick for it not to be a "remembered" error.

[budwich]

Re: Vizio E701-A3 Backlight Question

you have to go into the service menu to reset the error counter. There is a force on sequence... something like vol + Chan down at the same time while plugging in the set. Search for the exact sequence.

[Tjp444]

Re: Vizio E701-A3 Backlight Question

I've read through all the threads I could find, I've tried:

Vol-, input, plug in.
CH+ CH- press power, release power, release other buttons
Vol+ CH- then plug in

No success so far.

[Tjp444]

Re: Vizio E701-A3 Backlight Question

Reading through other Vizio and Sharp posts, it looks like it may be a PS problem. I'm only getting 165v across the legs of the filter capacitors, circled in orange in the attached pic. Is that low?
Thanks for any input.

[budwich]

Re: Vizio E701-A3 Backlight Question

I think the bl-er is generated towards the main board by the power board. If I see the picture of the power board correctly, all the pins going to the leds are visible and available (with care). You should be able to measure across each pairing just like you did with your tester. Note: the voltage may appear and disappear quickly.

There is a technique using a resistor to feed the ps-on line (resistor going to 3v supply somewhere on the board / connector) with the power supply to main cable disconnected. Then the light will stay on / light "forever" and you can see what the result is... maybe you have some additional leds gone. Lots of people replace whole strings as the "act of playing" causes issues for the "leftovers".

[budm]

Re: Vizio E701-A3 Backlight Question

Reading through other Vizio and Sharp posts, it looks like it may be a PS problem. I'm only getting 165v across the legs of the filter capacitors, circled in orange in the attached pic. Is that low?
Thanks for any input.

If the PS-ON is present (all the boards are connected) when TV is turned on then the DC V measured between the two legs of any of those 3 main filter caps should be 380 ~ 400VDC if the PFC boosted Voltage is working.

[Tjp444]

Re: Vizio E701-A3 Backlight Question

Thanks Bud. PS ON is high, BL ON is high, the voltage between the legs of the filter caps never goes above 168v. I ordered a tested replacement PS board with a warranty, apparently these can be repaired (shopjimmy sells a repair kit) but doing the math it made more sense to buy a board with a warranty. I just hope I didn't damage the panel taking it apart, I was extremely careful but you never know. Will report back.