Vizio M421VT LED no display
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Re: Vizio M421VT LED no display
I still have issues.
I left backlight disconnected (CN902,CN905) when I tested VLED voltage.
After pressing power it was 40vdc. for a second then dropped off.
I had the same results checking voltage with backlight connected.
From BudM-I think once the bridge rectifier is replaced to get the voltage for the LEDs you will be OK unless the circuts that drive the transformer also failed due to shorted out bridge.
What next?Last edited by ryan74; 04-29-2013, 01:26 PM.Comment
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Re: Vizio M421VT LED no display
So what voltage do you get at the +/- terminal of the bridge, it must be quite high since the filter caps are rated at 33uf 200V.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: Vizio M421VT LED no display
So, next step is to see if BLON comes on and stays high and also maybe DIM (I am not sure if this set modulates the voltage to vary brightness or uses PWM; it may use a combination of the two.)Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
For service manual, schematic, boardview (board view), datasheet, cad - use our search.Comment
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Re: Vizio M421VT LED no display
I pulled and tested bridge just to be sure. Everything tested as below except:
Pin 4 to 1 was .879V.
So, testing the bridge: Looking at device from top label side pin 1 is +, 2 and 3 are ~ and 4 is -.
Meter probes in order (red) (black)
Pin 2 to 1 you should see ~0.4V
Pin 3 to 1 you should see ~0.4V
Pin 1 to 2 you should see OL
Pin 1 to 3 you should see OL
Pin 4 to 1 you should see ~0.4V
Pin 1 to 4 you should see OL
Pin 2 to 3 you should see OL
Pin 3 to 2 you should see OLComment
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Re: Vizio M421VT LED no display
My error 4-1 is correct as there are two series diodes.Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
For service manual, schematic, boardview (board view), datasheet, cad - use our search.Comment
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Re: Vizio M421VT LED no display
The 40V reading at the output of the bridge seems too low since the filter caps are 200V rating.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: Vizio M421VT LED no display
I know transformers rarely go bad but could it be a bad transformer or most likely something else?Comment
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Re: Vizio M421VT LED no display
The capacitors on the output could be bad.Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
For service manual, schematic, boardview (board view), datasheet, cad - use our search.Comment
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Re: Vizio M421VT LED no display
or the drive circuit that drives the transformer is not driving it correctly, that is why I wonder if it gets damaged when the bridge shorted out.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: Vizio M421VT LED no display
I'd be surprised. Most drive circuits fail or work. Like shorted FETs. Won't work. A few exceptions, like bad coupling caps and current shunt resistors, of course.Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
For service manual, schematic, boardview (board view), datasheet, cad - use our search.Comment
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Re: Vizio M421VT LED no display
when I press power I get the 40v for a split second.
This may sound stupid but I don't know. The drive circuit for transformer- Is this the cold(north) side? or are you refering to the circuit before transformer?
I pulled all 4 caps in upper left of board(2-200v) and tested good.
200v 33uf=35uf
50v 47uf=48uf
Im stuck at this point but I think I found a board for $120 but Im not sure I want to give up yet.Last edited by ryan74; 05-01-2013, 04:45 PM.Comment
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Re: Vizio M421VT LED no display
The hot side, there are two MOSFETs and little IC for driving them, you can look up the spec of that IC.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: Vizio M421VT LED no display
I rechecked voltages:
------------
on/off-4.91v
dim - 2.93v
12v - 11.91v
12v - 11.91v
G
G
G
24v - 24.67v
24v - 24.67v
ps_on-3.09v
5.2v - 5.11v
5.2v - 5.11v
acd -
------------
Vled-194.7mV
all #- 10.65v
-------------
Vsync- 25mV
DIM- 58.5mV
G
DCLK- 49.1mV
G
I assume vsync and dim should be giving a reading and im not sure about ACD.
Now im thinking it is the middle board(pc/tcon?) or possibly main board.
http://www.shopjimmy.com/vizio-cbpft...2-pc-board.htm
these are the original readings from old board:
1)BL_on = 4.91V
2)BL_DIM = 2.93V
3)12V. = 12V
4)12V. = 12V
5)G = 20mV
6)G = 20mV
7)G = 20mV
8)24V. = 24.73V
9)24V. = 24.73V
10)BS_on = 3.09V
11)5V. = 5.09V
12)5V. = 5.09V
13)PWR_ok = 2.8mV
CN902
Vled = 235.6mV
#4-1 = 10.69V
#4-2 = 10.27V
#4-3 = 10.67V
#3-3 = 10.65V
#3-2 = 10.66V
#3-1 = 10.64V
Vled = 236.2mV
Cn905
Vled = 237mV
#2-1 = 10.25V
#2-2 = 10.63V
#2-3 = 10.64V
#1-3 = 10.66V
#1-2 = 10.27V
#1-1 = 10.67V
Vled = 237.0mV
Any idea how to test pc board? Theres a connector from main board but nothing listed by it.Last edited by ryan74; 05-13-2013, 01:21 PM.Comment
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by ivtecHi guys hope you all are having a marry Christmas ,i have here a Vizio M421vt that started to have some interference in the pic, nothing else is wrong ,i send a Utube video with the fault.Any clues and help would be appreciated.
https://youtu.be/YW1QeeCoSDA - Loading...
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