Vizio VP42 HDTV20A Plasma Mainboard problem?

[philliesfan30m]

I got this tv for free when i got it home i plugged it in and i only had the standby light. It has no response when the power button is depressed and no relays click when plugged in either. i took the back off and checked every fuse on all the boards and they are fine. when plugged in the only fuse that has voltage on the mainboard is f2 which has 5 volts on both sides. i don't think the mainboard is sending the pson or the power button is not working since it does nothing when depressed. i checked the voltages on the sot-223 voltage regulators and 2 other regulators on the mainboard here is what i got with the tv plugged in and using chassis as the ground.

u3 which is a az7805t which is a 3 terminal positive linear regulator to-220 package

0 volts on all pins and tab - center pin is ground and so is the tab pin 1 is input and 3 is output

u10 which is a 1084 0707hl which is a low dropout positive regulator to-263 package

pin1 1.39v pin2 2.66v pin3 4.44v
pin1-adj/gnd pin2-output pin3-input

u9,u33,u8,and u2 are all amc1117 which are also low dropout positive regulators sot-223 package pin1-adj/gnd pin2-output pin3-input

pin1 pin2 pin3
u9-0v 1.52v 3.24v
u33-2.04v 3.28v 4.44v
u8-2.06v 3.3v 4.91v
u2-2.05v 3.3v 4.44v

i also checked all of the diodes on the mainboard and d4 read 150 1 way and 1330 the other way and d52 read 50 1 way and 83 the other way but the might be in parallel with something i haven't checked closely or removed them to check off the board they are both surface mount diodes all the other diode read open 1 way and about 150 the other way. any help or direction as to where to go from here would be appreciated. the pics aren't the best but if needed of a certain area i will try to get the best pic i can to help troubleshoot.i would prefer to do a component level repair instead of replacing boards.

[philliesfan30m]

Re: Vizio VP42 HDTV20A Plasma Mainboard problem?

anyone have any ideas?

[philliesfan30m]

Re: Vizio VP42 HDTV20A Plasma Mainboard problem?

with the 5v standby jumpered to the pson the screen lights up sp i am guessing the mainboard is the problem but now i need to find out what on the mainboard is causing it to not send the pson signal. any help?

[philliesfan30m]

Re: Vizio VP42 HDTV20A Plasma Mainboard problem?

also the power key is working properly so it has to be the mainboard. i'm guessing it is the microprocessor isn't sending out the proper signal. anyone else have any input at all?

[philliesfan30m]

Re: Vizio VP42 HDTV20A Plasma Mainboard problem?

i didn't see 1 of the amc1117 regulators hidden under 2 caps that were slightly over top of it. it was u7 and it read .002,.098,and 3.28 volts so i knew that was the bad 1 it just took me a while to get the part. i replaced it and it came back to life. hope someone else finds this useful. oh and regulator u9 was a 1.5v fixed and all the other amc1117 regulators were adjustable just like the 1 i replaced. i didn't state that in my original post.

[philliesfan30m]

Re: Vizio VP42 HDTV20A Plasma Mainboard problem?

well i thought i had it fixed. now after the tv is on for a while times vary it could be on for 7 hours and sometimes on for 3 hours and then the picture goes out but the screen still glows with no sound and none of the buttons work either power,etc. when the picture goes out the control board has 4 leds for temp. sensoring i believe. when it is on and working fine it has the top 3 leds lit but when the picture and sound goes out then the top 3 leds go out and the 4th led on the bottom comes on. when i unplug the tv for a minute and turn it on it goes back to working as normal until whatever it is getting hot gets too hot and shuts it down. thats my guess. anyone have any ideas as to what may be getting hot and causing it to go into protect mode or make it lock up?

[philliesfan30m]

Re: Vizio VP42 HDTV20A Plasma Mainboard problem?

anyone?

[Caleb]

Re: Vizio VP42 HDTV20A Plasma Mainboard problem?

try it with a fan on it to see if some extra heat dissipation helps keep it on. is the main processor heatsinked? if not that would be my first guess.

[SlickClick]

Re: Vizio VP42 HDTV20A Plasma Mainboard problem?

have the unit open and on the stand... then when it begins to act up; turn it off get a car of Air; turn it upside down and "freeze" any really hot or suspect ICs and try to power on again and see if that clears up the issue then you will know the area that will need to be worked in on the circuit board...

[philliesfan30m]

Re: Vizio VP42 HDTV20A Plasma Mainboard problem?

thats what i was thinking caleb is that the processor was overheating because it doesn't have a heatsink on it why they would not heatsink the processor is beyond me especially knowing how hot tv's run or atleast have fans which are also not installed. i do have some heat sinks that will probably fit it so that is probably gonna be what i do next. slickclick i do have the back off and on the stand i was gonna try that but i ran out of canned air. when it loses the pic it still glows and stays powered on but if i unplug it then it goes back to being able to work properly when the power button is turned on. i didn't know if freeze spraying it would actually make the picture come back on when in that state because it seems like it gets sent an error saying it is overheating and locks up and even when freeze spraying it probably won't reset the error until unplugged. if that makes any sense. i do appreciate the replies!