Magnavox 40mf401b/f7

**budm** · 11-01-2012, 10:05 PM

Re: Magnavox 40mf401b/f7

Wait a minute, you are telling me that the bcakligts stay on now, I thought it flashes on then goes off.
Right now it looks like the T-CON board is dead or it is not getting the voltage feeding it.
The LCD panel looks like one of those built-in T-CON which is about impossible to repair, on the right side of the chassis, there is a board with metal shield on top with the cable running over to the LCD panel. Can you open up that shield to see if there is any fuse inside?

**ryan74** · 11-01-2012, 10:33 PM

Re: Magnavox 40mf401b/f7

i thought t-con was on top.
you might be thinking of the magnavox plasma tv im also working on.

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**budm** · 11-01-2012, 10:40 PM

Re: Magnavox 40mf401b/f7

The LCD panel in the picture does not look like it has replaceable T-CON board like typical LCD TV. I can see skinny little cable going to the top of the panel. This is the typical T-CON board for LCD PANEL:
http://www.shopjimmy.com/catalogsear...ARD&restrictBy[master+part+type]=T-Con

**ryan74** · 11-01-2012, 10:59 PM

Re: Magnavox 40mf401b/f7

i think i found part of the problem. and yes it looks built in so does that mean tv is shot?
if it is shot, the other boards should be good to sell right? you said voltages looked ok.

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**budm** · 11-01-2012, 11:23 PM

Re: Magnavox 40mf401b/f7

You sure did find the cause of the problem! I can see the fuse, but boy, how did the liquid get inside? Did you try cleaning the gunk off the board yet, may have some damaged traces that get eaten away that may be fixable, nothing to lose at this point.
There should be either 5v or 12v on that surface mounted fuse.

**ryan74** · 11-01-2012, 11:40 PM

Re: Magnavox 40mf401b/f7

i need to clean it up but what can i use for cleaner besides elec. contact cleaner from auto store?
i figure a soft bristle toothbrush would be good
it looks like a combination of rust, corrosion, and a little liquid still but i dont see any visual damage to board.

**budm** · 11-01-2012, 11:45 PM

Re: Magnavox 40mf401b/f7

I use denatured alcohol with soft brush. I hope the liquid did not get all the way into the panel.
I am sure glad that you show me the picture of the screen, otherwise you would have bought the inverter board for nothing.

**ryan74** · 11-02-2012, 02:00 PM

Re: Magnavox 40mf401b/f7

i cleaned everything up
it doesnt look that great but i have 12v on input to fuse and 0v. output.

the ceramic fuse is- Lf3a

im not 100% sure what to search for besides.
surface mount
3a
ceramic - rectangular
size - 6mm long, 3mm wide aproximatly

theres 12v going through fuse but i cant find 1 that small

this is all i can find.
http://www.mouser.com/Littelfuse/Cir...z0zlhtZ1z0rx8b
which one will work best?

**budm** · 11-02-2012, 03:30 PM

Re: Magnavox 40mf401b/f7

do you have something like 0.5 Ohms 1/4W resistor to use in place of the fuse?

**ryan74** · 11-02-2012, 03:33 PM

Re: Magnavox 40mf401b/f7

no i dont think i have any spare parts unless i can pull 1 off a couple old main boards i have.

i have a pb from a polaroid lcd
i think the fuse at loc F2 is 3a but its round and has leads soldered to it

**budm** · 11-02-2012, 03:36 PM

Re: Magnavox 40mf401b/f7

do you feel brave, jump it and see if it will come on. Or do you have any pigtail fuse?

**ryan74** · 11-02-2012, 03:56 PM

Re: Magnavox 40mf401b/f7

will this work?
im not sure how to identify resistors.
otherwise i have a 5a and a 10a auto fuse w/holder

i guess it wont hurt to jump it, but its not my tv

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**budm** · 11-02-2012, 04:02 PM

Re: Magnavox 40mf401b/f7

That will work, the LCD was so badly damaged, so you are doing your best, if it has shorts on the board, then it will not be practical to try to locate the short circuits anyway.

**ryan74** · 11-02-2012, 04:14 PM

Re: Magnavox 40mf401b/f7

that littlefuse is too big. i guess ill jump it for now. if it works ill still need help finding replacment fuse.

**ryan74** · 11-02-2012, 04:59 PM

Re: Magnavox 40mf401b/f7

i get constant 12v where i used jumper.
D7 has 12v on 1 side.
but still no change(white screen)

im willing to replace a few things and try to get it running.
D4 and D5(75351123) could be bad. they were covered in gunk.
i dont know if i have the soldering skill for those.

how do i check D4, D5, and D10?

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**budm** · 11-02-2012, 07:39 PM

Re: Magnavox 40mf401b/f7

D4, D5, D10 are Diode arrays, it looks like it has 5 Diode per package, they are used for signal line protection.
Since you are now getting the 12V all the way to the fuse, that means the section that you show as looking are OK, those pins are connected in parallel to supply the 12V to the fuse.
Can you read the numbers on the Diode. If I am correct, all the 5 pins on the top row should be connected to ground, you can Ohm them out. If they are connected to ground , then those top row will be Anode side of the Diode, each pin on the bottom row will be Cathode. Check to see if they are shorted out between the top row and the bottom row pins. I have a feeling there are problem somewhere else. There should some voltage regulators and switching power supply on the that board.

**ryan74** · 11-02-2012, 08:36 PM

Re: Magnavox 40mf401b/f7

diode #= 7535 1123

to ohm it out i set dvm to resistance. i only tested 1 lead so far(3.something). i couldnt hold meter leads, magnifier, and flashlight and got frustrated. i need 2 more arms.
ill try again tomorrow.

took pics of t-con up close.
the last inch of board is missing in pic 173

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**budm** · 11-02-2012, 09:01 PM

Re: Magnavox 40mf401b/f7

I see some regulator and switching power supplies and also some voltage test points. Please take the voltage readings on those test points.

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**ryan74** · 11-03-2012, 12:17 PM

Re: Magnavox 40mf401b/f7

the diodes D4, D5, and D10 i cant get a consistant ohm reading. not sure im doing it right. once i had 1.6Mohm next time i had 6Mohm.

i think voltages looked ok. i added measurments to pics.

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