Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
I rigged the resistor like you said, and the backlight came right on when I fired it up!
Only problem now is that none of the AV or Component inputs work, and the HDMI work on my Roku for showing the menu, but any shows I try to play shows a purple screen. There is sound, but no pic. I think from reading other forums that it means the HDMI signal couldn't get a secure channel.
TV tuner works fine for both digital and analog signals.
The MCU chip gets pretty toasty too, and I think...
not-a-real-repairman
Member
Last Activity: 10-22-2015, 02:53 PM
Joined: 10-13-2015
Location: Columbia, SC
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
I'm not sure I follow you here. Do I put the resistor on the pin coming from the main board, or on the pins where BL_On and PS_On go into the power supply?...Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
... also, is it worth looking into converting this into a SV472XVT (since those main boards are more prevalent)?
Looks like the same video specs, uses the same T-Con, power, and LED driver boards with only slight differences in the main board(SV472... adds WiFi/Ethernet, but it looks like the back of the XVT472 is already has a hole to accept the network jack -- label just covers over it on the back plate since this model doesn't use it.)Last edited by not-a-real-repairman; 10-20-2015, 10:51 AM.Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
Playing "Blue-Smoke Advocate" here -- is there a risk in just hooking up BL_On to PS_On? What components could possibly be harmed in the LED driver / LEDs?Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
How much of delay are we talking? I watched the voltmeter as I powered up the TV and timed how long it took the BL_On and PS_On pins to energize, and they both seemed to turn on as soon as the button was pressed.Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
It looks like it goes something like this:
BL_On pin <- Capacitor (to ground) <- Resistor <- Capacitor (to ground) <- Feed from MCU.
I've got the RF shield off the MCU, but it looks like there is a large heat-sink that I can't seem to remove. My guess is some sort of double-sided tape.
Any suggestions on the best way to get the heat-sink off so I can peek under it?Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
The regulators I mentioned, or any of them?
Any other theories as to where I should look to figure out why I'm only getting 1.0v instead of 3.3v?
(And is your info coming from personal experience, or some sort of diagram that I could get a copy of?)
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Last edited by not-a-real-repairman; 10-15-2015, 02:53 PM.Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
Like I said before, I was able to turn on the TV, wait a few seconds for the power supply to stabilize, and then disconnected the BL-On line from the main board to the power supply and jumpered PS-On pin to the BL-On pin. The whole thing lit up. Screen looks good with no cracks / fluttering / fading / etc.
My Roku showed the menus and I could queue something up to play, but it gave a purple screen when I hit play; from what I understand that means it couldn't make a secure connection to the HD processor....Last edited by not-a-real-repairman; 10-15-2015, 11:18 AM.Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
I didn't write them down, but I did confirm that the Pin1 to Pin2 voltage on the 1117 IC's was 1.25v.
I really think the problem is a component under the RF shield. I'll send what I find after work....Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
Part, Input (Pin 3), Output (Pin 2)
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U2, 5.09, 3.33
U3, 5.02, 3.27
U4, 3.27, 1.24
U5, 5.02, 3.25
U6, 11.84, 8.23
U7, 5.02, 3.32
I think I've followed the trace with 1.10v to the underside of the RF shield. There is a jump in component numbering of the regulators on the board; I can't seem to find U8 to U19. I'm assuming they're all under the RF shield and behind a white plastic square. I'll unsolder it tonight and see if...Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
1000uf 35v cap is all good. I think it's just the angle of the picture.
I did find that one of the 1117 voltage regulators (U4) doesn't have any voltage on pin 1. Don't know if that's because a feature isn't turned on or because it's fried. I'll try to capture all the voltages from the various pins and try to trace back where it's getting the 1.0v from when I get home tonight.Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
When I pull and isolate the "A B C" connector that goes from the main board to the PSU I still get 1.0v on the BL-ON output pin (it's the "B" wire) when the TV is on. No voltage when off....Last edited by not-a-real-repairman; 10-14-2015, 12:17 AM.Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
Attached are pics. I'll annotate them later....Leave a comment:
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Re: Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
The power supply is putting out all the right voltages (5v, 12v, 18v, 24v), so I doubt it's that.
The LED on/off pin is on the main board. It is sent from the main board to the power supply, which then routes it un-altered to the LED driver board.
I'm trying to trace how it gets 1.0v from the 5v that it gets from the power supply. It's probably a voltage regulator that has gone out controlled from the main chip, but I'm still trying to trace it back to the source.
I'll try...Leave a comment:
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Vizio XVT472SV No Backlight - 1.0v on LED Driver ON/OFF pin
I picked up a used Vizio XVT472SV TV. Logo goes from orange to white, audio is good, flashlight test shows picture but no backlight.
The LED Driver on/off pin from the main board is only giving out 1.0v. From another thread someone said this model needs 3.3v. Power supply is putting out all the necessary voltages.
Only other 3.3v supply I could find was the "PS On" pin that I guess tells the power supply to switch on. I tried to jumper the "PS On" pin to the "On/Off" pin and the backlight turned on and showed the picture.
I tried... -
Re: New Members - please post your introductions here
Name is Noah. I tinker in electronics and HAM radio. If it's broke, I'll at least take it apart just to see how way over my head it is. Every now and then I get it back together, and once it a blue moon I'll actually fix it.Leave a comment:
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