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Jack, Technician
Category: TV
Satisfied Customers: 9578
Experience:  40 years experience as audio,video repair and installation tech
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I have a magnavox 42mf437b flat screen that the back light

Customer Question

I have a magnavox 42mf437b flat screen that the back light inverters were not turning the back light on. I replaced them, master and slave, and the back lights work but after a few minutes the screen still fades to black. What would be causing this?
Submitted: 1 year ago.
Category: TV
Expert:  Jack replied 1 year ago.

Hello , my name is Jack
Perhaps I can help you with this problem but first i would have a few questions so could you please send me a reply when you are ready to proceed ?

Customer: replied 1 year ago.
I'm here.
Expert:  Jack replied 1 year ago.

Thanks , a few questions coming up ;

Expert:  Jack replied 1 year ago.

Did replacing the inverters make any changes or this was the original problem ?

When this happens , is the screen just blank with some background light or completely dark like when the tv is off ?

Customer: replied 1 year ago.
Replacing the inverters did fix the back light coming on. I can see the light throught the vent holes now, there is sound, but after less than a minute the screen goes completely black like the tv is off.
Expert:  Jack replied 1 year ago.

Light through the vent holes ???

Do you get any picture when the tv is on or only " light throught the vent holes " ?

Customer: replied 1 year ago.
When i first turn the tv on there is a picture, but it then fades away to black. Leaving the sound on but no picture. If i look in the top for the tv and the back, i can see the back lights are on.
Expert:  Jack replied 1 year ago.

This is rather odd then but it looks like beside the inverters you also have a t-con board problems .

Usually backlights are on or off but do not "fade away" , did you try the flashlight test ?

Expert:  Jack replied 1 year ago.

If not then do you happen to have a flashlight handy ?

Customer: replied 1 year ago.
when i first started this process but it wasn't clear if there was an image there or not. I could not see the backlights on so i replaced the inverters, now I can see the back lights on, even when there is no picture.
Customer: replied 1 year ago.
I just did it again and I can not see any image on the screen.
Expert:  Jack replied 1 year ago.

How did all this happen to start with , thunderstorm ,power blackout etc. ?

Right now it looks like this tv is seriously affected no matter what happened and its difficult to decide if the power board , t-con board or main board is at fault (beside the inverters )

Do you have a voltmeter ?

Customer: replied 1 year ago.
It actually started out of the blue, where the screen would turn blue first then cut out. It would stay on if I went through an on/off cycle several times. I can get a voltometer but not versed as to how to use it.
Expert:  Jack replied 1 year ago.

No problem , in any case I just looked at the power board and there are no voltages whatsoever marked down on it like there usually are so this would be chasing your tail if you are not "very" familiar with a voltmeter and what to expect to read on the power board .

Right now my first suspect would be that t-con board if you want to give it a shot .

There are 2 versions of it and the part numbers are CMO 35-D016766 (V420H1-C07) or CMO 35-D014118 for the other

Expert:  Jack replied 1 year ago.

You would need to check the numbers on the bar coded sticker on yours and with that number that board can be bought for around $35

Customer: replied 1 year ago.
maybe I better go have a tech look at/ test them rather than just keep replacing possible programatic parts?
Expert:  Jack replied 1 year ago.

I was actually getting down that path and even a bit further like ;

Is there any way you can return those inverters and get partially refunded if not completely ?

Where did you get them ?

Expert:  Jack replied 1 year ago.

What I`m getting at is that your tv seem to have a major sickness and you can buy a new 42" tv with all the bells and whistles for $300 or less while this one could cost you $200+ to have it repaired

Expert:  Jack replied 1 year ago.

Wish i had an easy solution for you today but i hope this still help figuring out your next step and I will be in standby if you have any questions.
Thank you and please take the time to rate my answer if that answers your question and you can still reach me here at anytime after this chat is closed if you have other questions.

Please note that from where i`m sitting there is just so much that i can do and if you are going to rate my answer below O.K service then please do not rate at all , just let me know.

Customer: replied 1 year ago.
but not worth returning as it would cost more to ship them back than they cost. If the picture initially come up but then fades to black, would that suggest that the is not an issue with the actual screen? Absolutely get you point at this point I only have about $75 into it for the inverters.
Expert:  Jack replied 1 year ago.

Fading out would be the t-con first then the main board but the voltages on the power board would need to be checked

Expert:  Jack replied 1 year ago.

Not sure if that helps but we are back at the voltmeter and/or trying a t-con board

Expert:  Jack replied 1 year ago.

If you don`t have any more questions for now then please do take the time to rate my answer , this is how I make a living and that rating gets me paid for my time.
Also note that it will not close this post , you can come back here at any time if you have questions.
Thanks for understanding .

Expert:  Jack replied 1 year ago.

Thanks again