Vizio 42" M420SL works then goes blank

[pdsterns]

Good Morning TV'ers

Vizio usually starts and works fine for a few minutes then goes blank. Checking voltages when shutdown it reads 5v on the standby pins on the PS and 12v on the 12v pina, backlights are out now. What can I conclude or where to next.

Thanks in advance
burns

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

check the big capacitor on powerboard, carefully VERY HIGH VOLTAGE THERE, meter set to dcv probe on each leg, see what voltage you get with tv powered on, see If its around 400 or so, see what the voltage is while its working and after it shuts down.

[pdsterns]

Re: Vizio 42" M420SL works then goes blank

This time the TV did not power up. Nothing there, zero on 200 vdc scale. Checked the 12v and its still there

burns

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

did you set the meter to above 200, whats next 400? try that if you didnt.

[pdsterns]

Re: Vizio 42" M420SL works then goes blank

Yup, meter on 600vdc, nothing there

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

saw a similar board, maybe try UNHOOK cable from powerboard to mainboard, use 3 around 1K resistors to jump from pwr-on to stby, bl-on to stby, c-dimming to stby, plug power cord in and see if you get proper voltages and backlights come on and stay on.

[pdsterns]

Re: Vizio 42" M420SL works then goes blank

How can I get into those pins with that tiny connector? and if all were ok does it indicate a PS problem or a MB problem? I'm willing to buy a board I just don't know which one, maybe even Tcon

Update: The TV came up, with no jumpers, and I measueed across the big cap and it has 380vdc

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

thats what the test in post 6 can determine, if backlights come on and stay on with that test, then your powerboard and backlights are prolly ok.

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

what I have seen mostly when tv works for a few minutes before going blank is bad cap/s or backlight issue, try heating the capacitors on the powerboard with a hairdryer, start with the ones closest to the connector, heat them for a couple minutes then try the tv, see if theres any difference, DON'T wait til it cools to try it, do it while its hot, also check all the solder joints, examples of bad joints there: https://www.google.com/search?q=bad+...ih=607&dpr=1.5

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

also you can try turning down the backlights or brightness, turn them way down if you can in the short time it remains on, then see if the tv stays on for a longer period than it did before.

[pdsterns]

Re: Vizio 42" M420SL works then goes blank

what I have seen mostly when tv works for a few minutes before going blank is bad cap/s or backlight issue, try heating the capacitors on the powerboard with a hairdryer, start with the ones closest to the connector, heat them for a couple minutes then try the tv, see if theres any difference, DON'T wait til it cools to try it, do it while its hot, also check all the solder joints, examples of bad joints there: https://www.google.com/search?q=bad+...ih=607&dpr=1.5

Heating the caps near the connector yielded a steady ON and I was able to turn it off and on repeatidly. So does it come down to just needing a PS board or replacing the caps, there are 2 small ones and 2 larger ones.?

[pdsterns]

Re: Vizio 42" M420SL works then goes blank

WOW, heated about 10 times now, 100% success rate

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

cool, yep just replace those caps, should be good to go then, sure, replace all 4 with good quality low esr 105 caps, they might not all 4 be bad but who wants to keep going back in just for the cost of a few caps.

[pdsterns]

Re: Vizio 42" M420SL works then goes blank

Well there are 3 different size caps there and 9 overall and since I don't have any and don't even know if the is conformal coating on the back of the board making it difficult I think I will opt for a replacement board unless you suggest the larger or smaller ones etc. Just thinking of the easier option here. Thoughts?

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

your call, the thing about a replacement board is the caps are probably also 10 years old, they're not too hard to change, but if not soldering often maybe practice on a scrap board, suppose you could isolate which one/s need changing by isolating which ones let the tv turn on when heated, like only heat one or two at a time to isolate the bad one/s, its not a huge tv so if you had to change another cap down the road, no big deal.

[pdsterns]

Re: Vizio 42" M420SL works then goes blank

Well I was going to try and isolate to a particular cap or two and replace them hoping it was the larger ones but now the TV works normally after heating the caps with the hair dryer. Just a temporary situation, I am sure, so I think I will take the easy way out and just buy a board. Guys thanks for your help, I have an LG to fix next, lol, picture, no sound 55LB6300

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

for sound issue try, turn off tv, unplug any accessories, cable box, dvd, etc. unplug tv from power, press and hold power button for 30 seconds, plug tv power back in and try it.

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

can also go into your sound settings, look around in there, make sure internal speakers are selected, might also be a reset sound and maybe a sound test in those settings somewhere.

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

Well I was going to try and isolate to a particular cap or two and replace them hoping it was the larger ones but now the TV works normally after heating the caps with the hair dryer. Just a temporary situation, I am sure, so I think I will take the easy way out and just buy a board. Guys thanks for your help, I have an LG to fix next, lol, picture, no sound 55LB6300

this is strange, did you let it sit off overnight, then let it run a few hours?

[nomoresonys]

Re: Vizio 42" M420SL works then goes blank

there is a "dirty" test for those caps, set your meter to 20k ohm setting, put a probe on each leg, the meter should read a steady rise or fall, switch probes and watch should be steady rise or fall, just switch probes back and forth and see what you get, the one/s that seem to act different than the rest are prolly the culprit.