Magnavox LCD TV power fluctuation

[dman623]

I have a Magnavox LCD TV It was working fine and then it stopped. The red light would come on I would start the TV and it would start to turn on and then just turn off and the red light would go out. If I left it unplugged for a while and then plugged it in again I would get the red light again, but it still would not turn on. I opened it up and saw that the capacitors on the power supply were bulging.

So I went to my local radio shack and bought three new capacitors and replaced them. Now when I plug the TV in it makes the power-up energize sound and then stops and then does it again and again and just keeps repeating. The red light on the power button flashes with this as well and so I can't power on the TV at all.

I'm really not sure if it is possibly the wrong capacitors (although they have the same specs), a bad soldering connection, or something else.

Any ideas?

[tom66]

Re: Magnavox LCD TV power fluctuation

Aiiii! Sorry, but RadioShack capacitors are never to be used in any TV.

They are not low ESR which can cause problems for power supplies and likely to fail shortly as they are the bottom of the barrel picks from whoever's cheapest on the day.

However your problem may be related to some diodes on the power supply.

Start by posting a picture of your power supply.

[budm]

Re: Magnavox LCD TV power fluctuation

Model number of the TV will help also.

[dman623]

Re: Magnavox LCD TV power fluctuation

Thanks for the quick replies. I will take a picture and post the model number as soon as I get home today. As for Radioshack it was all that was immediately available to me. If I can at least determine that it is only caps then I can order some decent ones. Thanks guys.

[dman623]

Re: Magnavox LCD TV power fluctuation

The model #: 32MF337B/27

And pictures of the board with and without flash (apologies for the third one I didn't notice it was blurry)

http://i1146.photobucket.com/albums/...s/IMG_4028.jpg

http://i1146.photobucket.com/albums/...s/IMG_4027.jpg

http://i1146.photobucket.com/albums/...s/IMG_4026.jpg

http://i1146.photobucket.com/albums/...s/IMG_4025.jpg

[Mr Bill]

Re: Magnavox LCD TV power fluctuation

Can you re-upload the photos using manage attachments. I saved the one photo to my computer and its stretched out. Other members don't like images posted inline beacuse there isp providers have a data cap. Try and get the pictures as close to 2000 x 2000

[dman623]

Re: Magnavox LCD TV power fluctuation

I've changed the previous photos to links only for those who prefer and have uploaded them with manage attachments. Thanks for letting me know.

[Mr Bill]

Re: Magnavox LCD TV power fluctuation

I've changed the previous photos to links only for those who prefer and have uploaded them with manage attachments. Thanks for letting me know.

I'm surprised you got nichicon caps from radio shack. I've only ever seen at my store the lelon brand. The datasheet for the 3 caps you replaced are general purpose and not low esr so this might be your issue. Have you taken Tom's advice and checked any of the diodes yet?

[tom66]

Re: Magnavox LCD TV power fluctuation

Also they're axial caps... how on earth did you get them to fit?

I have heard of Radioshack selling Nichicons but never seen first hand evidence... hmm... if only they were competent enough to stock decent Nichicon series caps, maybe less stuff would end in landfill.

[dman623]

Re: Magnavox LCD TV power fluctuation

I've done my best to look at the diodes and none of them seem to have obvious problems. Radioshack only had one radial so I had to use the axials instead. They had long leads on them so the fit was fine.

I'm going to poke around on the site for a good place to buy caps and which brands and such, but if anyone has links handy that would be great.

Any other ideas for testing the power supply? As for the diodes am I looking for burned/scarred diodes?

[Mr Bill]

Re: Magnavox LCD TV power fluctuation

Digikey amd Mouser are the "coke" & "pepsi" around here . You can check the diodes with a digital multimeter if you have one and see if one reads shorted. I would change all the caps and go from there.

[dman623]

Re: Magnavox LCD TV power fluctuation

The only other areas that look like they've burned is one of the cooling fins and one of the connections on the converter.

[Mr Bill]

Re: Magnavox LCD TV power fluctuation

Also they're axial caps... how on earth did you get them to fit? .

That's a good point. Dman, is there clearance between the one lead on this cap and the jumper on the board?

[dman623]

Re: Magnavox LCD TV power fluctuation

That's a good point. Dman, is there clearance between the one lead on this cap and the jumper on the board?

There is but it is probably a bit closer than it should be. I didn't think about that part when I fit them in there.

So I've narrowed it down to aluminum electrolytic, 1000 uf, 35v, radial caps which gives me 193 results. As far as the temp I only know that it needs to be up to 105 degrees but I don't know about the minimum temp. How about the tolerance? Should I also try to get the same dimensions as the original or does that not matter too much? As far as brands go I've heard that Panasonic and Nichicon are pretty good so I guess I'll stick with those. Thanks for all your responses.

[tom66]

Re: Magnavox LCD TV power fluctuation

Add Panasonic FR to your search term to limit it down to a known good, recommended low ESR cap.

[Mr Bill]

Re: Magnavox LCD TV power fluctuation

If have a set of dial calipers you can measure the caps diameter/height that you have and narrow it down. list the all the caps you have and a rough diameter and height and we can give you some links for order. I see in your picture the other caps look like elite and they are no better than the raido shack caps.

I forgot to mention that Digikeys shipping is about $2 for fist class mail where as Mousers shipping is usually about $6. Most choose Digikey over Mouser but sometimes Mouser will have a component that Digikey doesn't have.

[dman623]

Re: Magnavox LCD TV power fluctuation

This is what I have it narrowed down to. It's just a link to mouser, but on your suggestion I suppose I need to look at digikey.

http://www.mouser.com/Panasonic/Pass...z0sq5yZ1yzvjj0

The diameter of the originals is about .5 inches or about 1CM and the height is about 1 inch or about 1.5CM

And now that you mention the other caps it actually looks like one of the smaller capXon caps has a little spot in the middle as well so it is probably bad. It is a 220uf 35v cap.

[Mr Bill]

Re: Magnavox LCD TV power fluctuation

Looks like that cap could be popped. Didn't see that from your pics the first time. Post the values of the other 4 caps (Uf & V). We know you need (3) 1000uf 35v caps. You don't need to replace the large cap.

[dman623]

Re: Magnavox LCD TV power fluctuation

2 x 33uf 50v

1 x 1000uf 16v

[Mr Bill]

Re: Magnavox LCD TV power fluctuation

is the 1000uf 16v part of the 3 that you replaced from radio shack? You do need a 220uf 35v cap too right?