Vizio LED xvt553sv

[mnpdreed]

Re: Vizio LED xvt553sv

Here are the components I traced from the Tcon ribbon. First pic is normal second pic is under a magnifying glass. Leaves the ribbon and hit R5 first. The left side of R19 and bottom R4 and emitter on Q1 is ground.

[mnpdreed]

Re: Vizio LED xvt553sv

Here what I came up with.

[mnpdreed]

Re: Vizio LED xvt553sv

Here is the main board pic. From the TCON ribbon I traced these components and the voltage is read with chassis ground. Power on Do you think it is here or keep tracing. Thanks

[mnpdreed]

Re: Vizio LED xvt553sv

R5 is reading 9.93K ohms R4 10.3K ohms

[budm]

Re: Vizio LED xvt553sv

OK Q3 is the one that passes the 12V from the Source pin to the Drain pin when Gate pin is pulled low but right now the Gate is sitting at 11.3V so the Q3 is not turned on to supply 12V to the T-CON. I see the GATE of Q3 is connected to the Cathode of D2 and I also see a via (small copper pad with very small hole) that should be going to some where on the board. If you ground the GATE of Q3 through 100 Ohms (100~500 Ohms) resistor, then you should see the 12V to the T-CON, so do that and see if you do get the pictures on the screen.

[mnpdreed]

Re: Vizio LED xvt553sv

Ok will take a few . I will have to go pick up a resistor. Don't have one. Thanks

[mnpdreed]

Re: Vizio LED xvt553sv

I found a 680 ohm resistor on an old power supply will that work?

[mnpdreed]

Re: Vizio LED xvt553sv

I found a 100 ohms as well. So I connect the resistor to ground and gate of Q3. Is this correct

[budm]

Re: Vizio LED xvt553sv

Yes.

[mnpdreed]

Re: Vizio LED xvt553sv

It did work so where do I go from here.

[budm]

Re: Vizio LED xvt553sv

OK, that's good the T-CON is OK and working and you are getting the pictures on the screen OK, just bad ON/OFF signal for that Q3.
BTW, great job tracing out the connections.
You will now need to find out where the GATE connection goes beside to the Cathode of D2, that will be the key.
Or you can leave the resistor in place since I expect something else on the main board to go bad later when one function already failed, get the new main board after another function fails.

[mnpdreed]

Re: Vizio LED xvt553sv

Thank you. I could not have did it without you and a magnifying glass. So if I leave the resistor it will be ok ? I think I will continue tracing it. So I need to start from the gate and keep tracing

[budm]

Re: Vizio LED xvt553sv

"So I need to start from the gate and keep tracing" Yes, it is probably be connected to another switching device.

[mnpdreed]

Re: Vizio LED xvt553sv

If I have 11.3 v at the gate and cathode of D2 what what will
Make it cause the drop down to 28 m V on the anode side of D2 going to Q1 collector. Just trying to see direction the current is running

[budm]

Re: Vizio LED xvt553sv

The anode side of D2 is low because Q1 is on (because it has 0.6V to forward bias on the B-E junction) so the Collector voltage is pulled LOW, the D2 is in reverse bias so it is not affecting the Gate voltage. The GATE Voltage is pulled low by other circuit, not by Q1.

[mnpdreed]

Re: Vizio LED xvt553sv

I had a mix up on the first trace I did. D2 cathode not only connects to the gate of Q3 but also connects to C9 and R14. Also Q1 collector not only connects to D2 but also connects to R14 and R13. Sorry about the mix up. Will this change anything on what you think is going on with it. The revised drawing has the new connection paths highlighted in yellow. Thanks

[budm]

Re: Vizio LED xvt553sv

What is the resistance of R13, R14?
Also see if the Collector voltage of Q1 goes high (>10V) when the TV is OFF.

[mnpdreed]

Re: Vizio LED xvt553sv

Attached pic has info. The reading of R14 on the original main board read .407M ohms different from the refurbished board in the TV

[budm]

Re: Vizio LED xvt553sv

OK, that does not make sense that Collector Q1 Voltage barely goes up when it is off (Vbe of 0V)
"The reading of R14 on the original main board read .407M ohms different from the refurbished board in the TV" What is the reading on the refurbished board then?

[mnpdreed]

Re: Vizio LED xvt553sv

19.3 K ohms