Re: Vizio M420NV no backlight
Update: in attempts to evaluate the mainboard, I found that
1: given my knowledge level, and lack of detailed schematic, I had no reasonable hope of identifying the failed component, and
2: if the component was identified, successfully replacing it on the board has a much lower chance of success, and likely much higher cost than piggybacking another power signal as budm suggests.
I cut the BL_ON, and jumped it to the REMOTE ON signal with the 1k. Pin 11, 3.2v when powered on.
I really appreciate your help,...
sricechex
Member
Last Activity: 03-07-2021, 06:58 AM
Joined: 03-21-2018
Location: Springfield, TN
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Re: Vizio M420NV no backlight
Will do. May take some time to get to it... Got a fussy baby occupying my attention.Leave a comment:
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Re: Vizio M420NV no backlight
Yes, Sir; disconnected all cables from MB. still mounted on chassis. 0.62kLeave a comment:
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Re: Vizio M420NV no backlight
GND to BL_ON = 0.6kohmLeave a comment:
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Re: Vizio M420NV no backlight
Ooo, that makes sense. You've done this before, haven't you?
From the information I have, is there any reason to suspect any particular board components? For example, in that functions are good, but effective BL_ON voltage is low, is there reason to explore regulators vs. eeprom or fuses?
I certainly appreciate what you're suggesting, Budm. That method of repair certainly would be cheaper than all else, and...why not do that.Leave a comment:
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Re: Vizio M420NV no backlight
I haven't made time yet to try all functions, just menu functions, and successful HDMI input. When I get back to it I'll try different input and audio.
Are you thinking of any specific functions?
Where would you suggest sourcing the other signal?Leave a comment:
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Re: Vizio M420NV no backlight
Budm, that's what I did this morning, and the backlights work great! Ran off my Raspberrypi just fine. Thanks for the input.
I had only a minute before work, so haven't been able to play with the other posts yet. I want to see if I can gain some experience isolating the culprit component(s) with some more precision.
If it promises to be too frustrating or expensive, I'll just jam that resistor back in.
That will keep my sunk cost at $25.01...not too shabby.Leave a comment:
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Re: Vizio M420NV no backlight
Great, dude, thanks. I'll let you know if I learn anything useful for future projects!Leave a comment:
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Re: Vizio M420NV no backlight
This tv is certainly not worth a $100 mainboard ($25 pawnshop special), but in that I got it just for the learning, I'm tempted to swap the eeprom, if I can have some confidence that a failed eeprom is the culprit.
Any thoughts on further testing on the mainboard?
I greatly appreciate your input, nomoresonys and budm. You guys are kind to lend your expertiseLeave a comment:
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Re: Vizio M420NV no backlight
The backlights do come on with a 1k between BL_ON and 5VSB!Leave a comment:
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Re: Vizio M420NV no backlight
Nothing happens when I disconnect the motherboard from the power supply and plug in.
In regards to the resistor test in post #8, my board lists no "PS_ON," as far as I can see. Are any of these other pins indicators of a ps_on?...Leave a comment:
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Re: Vizio M420NV no backlight
Thank you for finding that video. I haven't gotten to the unit this evening yet, I'll keep you posted.Leave a comment:
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Re: Vizio M420NV no backlight
If the backlights do work when forced, I'll give the eeprom-swap a try. I'll report relevant information as I find it.
Is the standby voltage what should be expected in a live signal?Leave a comment:
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Re: Vizio M420NV no backlight
I think he was taking about BL_ON , Not PS_ON?
That certainly makes sense, I'm just inexperienced as to what voltage constitutes "getting no signal. "
I'm getting 0.8v, but should it be a known board signal voltage like 3.2 or 5v?Leave a comment:
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Re: Vizio M420NV no backlight
Great! Thank you, nomoresonys. I'll give that a shot.
If I can confirm that the backlights can be forced on successfully, can I be relatively confident that there is an eeprom failure on the mainboard? (is there a source for ideal voltages at those signal pins?)Leave a comment:
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Re: Vizio M420NV no backlight
I know this was a while back, but I thought this may be a source for diagnosing an almost identical problem.
I have a m420nv with no backlight, good image, white logo.
VLED voltages of 164v.
BL_ON from 0.4v off to 0.8v on.
Does this sound like an eeprom failure on the main board?
Is there further diagnostic information necessary or suggested?
Thanks!Leave a comment:
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Re: New Members - please post your introductions here
Well, hello, badcaps.
I've actually used information from this site to fix a couple LCDs, and now I'm hooked. I love getting these things on the cheap, and keeping them out of the dump. Also, it makes my brother jealous when I get a new tv for $40.
I would like to take this hobby to the next level of diagnosis, but don't know where to go to find board properties such as nominal voltage values.
I also currently have a vizio with a failed backlight I'm hoping to find a little guidance on prior to ordering components....Leave a comment:
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