M421VT LED Screen Color Distortion

[dfang]

Re: M421VT LED Screen Color Distortion

Ok so I jumped 5v to on/off pin and 5v to PS_ON as well ..the results are still no 24v,,, of coarse no LED back lights...This is what I've got for voltages at PS now..
ON-OFF=4.24vdc
DIM=3.28vdc
12v=2.52vdc
12v=2.53vdc
GND=0vdc
GND=0vdc
GND=0vdc
24v=0vdc
24v=0vdc
PS_ON=4.24vdc
5.2v=5.14vdc
5.2v=5.14vdc
ACD=0vdc

[tom66]

Re: M421VT LED Screen Color Distortion

What range are you using on your meter? Can you test using the 200V range instead? (If it's autoranging, ignore this.)

[newtothis]

Re: M421VT LED Screen Color Distortion

I was thinking same as you Tom but the 5v is showing correctly so dismissed it

[tom66]

Re: M421VT LED Screen Color Distortion

Crazy thought, but what if, for example, the left most "1" digit on his meter did not work properly? This would rule this out...

[newtothis]

Re: M421VT LED Screen Color Distortion

Crazy thought, but what if, for example, the left most "1" digit on his meter did not work properly? This would rule this out...

Hmmm,

If you cant do as Tom asked and set too 200 range -

can you confirm 0v on the 24v rails after forcing the backlights on?

If that is that case tom we should see ~4v otherwise the PSU is indeed at fault

[dfang]

Re: M421VT LED Screen Color Distortion

I've got Fluke ET-23 a old one,,but,,it works fine...It's manual ranging..I tried all ranges ..Could the PS power on voltage need to be greater than 4.24 volts ? I looked on the net for a main board and couldn't find one ,,,every one is out of stock...Must be a run on these babies..

[newtothis]

Re: M421VT LED Screen Color Distortion

So what exactly does it show on 200 range?

[dfang]

Re: M421VT LED Screen Color Distortion

Ok,,first off I guess my Fluke is autoranging...I did a test with jumper resistors and realized that when the set is first plugged in the VIZIO logo will blink bright white 35 times then stop,,it is the back lights blinking...With meter on one of the 24v lines at the PS,,I see the voltage as high as 11.72vdc,,but it happens so fast the meter can't read the full correct voltage..After the 35 blinks and press TV power on backlight gives a very quick flash and that is it until you unplug/plug in and it starts the dance again..So the PS must be capable of lighting the backlights ,,,just will not stay on..

[newtothis]

Re: M421VT LED Screen Color Distortion

Ok so that confirms the PSU is shutting down for some reason.

Not sure if the PSU will stay on without the backlight load but try disconnecting the backlights from the PSU and forcing it on again

[dfang]

Re: M421VT LED Screen Color Distortion

Ok so that confirms the PSU is shutting down for some reason.

Not sure if the PSU will stay on without the backlight load but try disconnecting the backlights from the PSU and forcing it on again

Humm...disconnected backlights from PSU and forcing it on I get nothing on 24V lines... I reconnected backlights and now not even varying voltage on 24v pins on PS connector when plugged in.. I'm doing harm to this tv..

[newtothis]

Re: M421VT LED Screen Color Distortion

Humm...disconnected backlights from PSU and forcing it on I get nothing on 24V lines... I reconnected backlights and now not even varying voltage on 24v pins on PS connector when plugged in.. I'm doing harm to this tv..

Varying voltage? You listed it as 0v every test

[truep]

Re: M421VT LED Screen Color Distortion

Maybe the ac detect is shutting it down??

[truep]

Re: M421VT LED Screen Color Distortion

That's the acd pin

[dfang]

Re: M421VT LED Screen Color Distortion

I'm back to square one,,,I found a bad connection with my resistor jumpers at Main board connector..
Now with forced PS operation I get 14.47v at 24v pins...backlights blink off and on rapidly when tv is plugged in..Used DVA adapter on my Fluke to capture the max voltage..Something is shutting down PS...Don't know what else to try ..

[dfang]

Re: M421VT LED Screen Color Distortion

Any more suggestions ? I hate to give up,,but,,looks like the cost of boards to try (if they can be found) are not worth the TV..I do appreciate the help and did learn some things for future repair attempts..

[newtothis]

Re: M421VT LED Screen Color Distortion

This is with main disconnected correct? And the backlights are flashing with jumping volatges?

Do you have 2 jumpers in place? One for PS_ON and one for backlights?

[dfang]

Re: M421VT LED Screen Color Distortion

This is with main disconnected correct? And the backlights are flashing with jumping volatges?

Do you have 2 jumpers in place? One for PS_ON and one for backlights?

I have jumper for PS_ON and ON-OFF..

[newtothis]

Re: M421VT LED Screen Color Distortion

I have jumper for PS_ON and ON-OFF..

Ok remove jumper to ON/OFF and retest voltages, They should come in spec. Reconnect main and make sure we are back to the original fault

[dfang]

Re: M421VT LED Screen Color Distortion

Ok remove jumper to ON/OFF and retest voltages, They should come in spec. Reconnect main and make sure we are back to the original fault

Ok,,,disconnected ON/OFF jumper but left 5.2v jumped to PS_ON at main board connector,,,,no voltage on 24v pins at PS connector and no backlights..

[newtothis]

Re: M421VT LED Screen Color Distortion

What I expected to see, Reconnect main and make sure we are at the original fault.