Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

[lookimback]

I got this TV a few days ago and nothing would happen when you turned it on. I opened it up and found 3 bad caps on the power board. I replaced them with the appropriate Panasonic FMs. Now the TV will power on and I can go through the menu options, screen is OK but inputs don't work. The input buttons also don't seem to do what they are supposed to either. I took the main board out and inspected it and found a chip that has a small crater burned into it. Actually it was bubbled up but I scraped the top of with my fingernail. I'm pretty sure this chip is the problem but I can't read the numbers on it.

[johnboy1313]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

It's L5973D. You can get it from Digi-Key. There is a pad under the chip too. You need to heat the entire chip up to get that pad to free up. I didn't and I pulled the pad off of the board and ruined it. I then had to buy another board.

https://www.badcaps.net/forum/showthread.php?t=28636

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

Thank you. I was just coming back to post that I had found that very thread. Now I need to see who's got the part.

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

Well, my new chip came today. I removed the old one with my rework station. I soldered the new one in and then heated it with the rework station's heat wand to solder the ground pad under it. Everything went smooth and looked good until I plugged it in. The new chip burned exactly where the old one did. I'll have to find a data sheet to figure out which pin it was that burned. If you were holding the chip so you could read the numbers, it would be the 2nd pin from the left. I guess that would be 2 or 7.

Edit: OK, I found the data sheet. Its pin 7 (ground). In my experience with electrical wiring, I've often found that the ground wire, rather than hot wire, will burn out when a load draws too much current. So maybe the chip is drawing too much power. Perhaps something is shorted to ground? Anyone else experience this?

[freakaftr8]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

Check diodes in the area or off the pins to the ic. One could be shorted both directions. Perhaps a diose coming off pin 1.

[jetadm123]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

Since the new chip is burned out, I suggest removing it and with your meter, check each pad to see if it's shorted to ground. Obviously, pad 7 will show a short.

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

I didn't realize I had replies. Thanks for the advice. I'll try removing the chip and testing with my meter as soon as I get home. Next time I find a burned chip I'll do that before I install the new one as well.

[wreksta]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

I woud also measure the voltages on the psu mainly the connector for the main board cable

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

I've attached a pic of what might be SMD diodes. If they are then I might be better off parting out the boards that I know are good. Reason I say that is because I tested every one on the board, both sides, and at least 15 gave me readings in both directions. This TV sat on a desk in a finished basement for several years after it quit working. I already replaced 4 bad caps on the power board. Voltages are about 18v except for one 6v terminal. I'm thinking the humidity might have caused a lot of problems. That being said, there are no physical signs of corrosion and I did get this TV to power on after refurbishing the power supply. I just couldn't get past the menu. Now I can't even get that. If the components in the pic are diodes, how would I determine what to replace them with? Whether or not I continue working on this would depend on what they cost. So far I have about $30 invested.

[freakaftr8]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

In most cases readings in both directions are normal add they have a resistor in parallel. The diodes you will be looking for are a dead short both directions.

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

So those were diodes then? I tested all with multimeter set to diode and then again with meter set to continuity. Didn't find any that were shorted like that.

[Nola_Gal]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

Going through my own Magnavox nightmare at the moment. Same model only a 50 inch. I think elves made these.

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

OK, with the chip removed, I have 19v on what would be pin one. This is output and should probably be 0 without the chip.

Edit: I was mistaken. I don't have voltage on pin 1. Pin 1 is grounded.

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

Anybody got the data sheet for the power supply?

[budm]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

With the IC removed, What resistance do you read on the pin1 pad and pin 7 pad? Inside the IC there is power MOSFET with Source and Drain between pin 8 and pin 1, it is being used as high speed switch, if pin 1 is feeding into shorted o very low resistance load, it will burn up the MOSFET inside the IC.

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

0.533k

[budm]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

That is only 500 Ohms, unless it is not switching and the MOSFET is just stuck in the ON mode. What resistance do you get at pin 4 and 7?
btw, that diode 6001 show 500 Ohms on both direction? May be should be tested off he board.

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

Haven't had time to get back to this yet. I think I might just have to put this one down. When I removed the chip the first time some of the pads lifted off the board. They were still connected so I just smoothed them out and soldered the new chip in place. When I removed the second chip, 3 pads came with it. I guess I should have epoxied them back to the board when I had the chance. 2 of the pads aren't important, they don't connect to anything. The third I could probably jump with some thin wire if I had to. It would be under a 1/4" long. Thing is, its got a good size scratch on the screen. Can't see it when its on but its real ugly when its off. I'm sure that affects the value significantly. I have $35 invested already. If I have to replace the chip and the diode(if that's it), that would be about $45 invested (if I can salvage the board). I'm sure I could only get about $75 for it with the scratch. If I can get the scratch out, maybe I could get $125. That would be worth it then. If I had to buy a board, I would lose money. I know the power board is good (I rebuilt it already), Tcon, both inverters. I could probably sell them and the base on eBay and get at least $100. I might try to get the scratch out and go from there. I just hate to give up.

[johnboy1313]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

How do you remove a scratch? I haven't had any luck in that department

[lookimback]

Re: Magnavox 32mf231d/37 bad chip found but cant identify because numbers are burned.

I haven't tried yet but read online about using a new (unused) pencil eraser. Also, a mild solution of isopropyl alcohol and water is said to desolve the anti-glare coating and cover the scratch. You don't want it too strong or it will make it worse. I haven't tried either of these yet and would suggest Googling LCD scratch removal to find correct ratio of alcohol/water. Also, try on a junk screen first if you have one.