Olevia 237-T12 working fine but shouldn't be.

[lookimback]

I know that is a crazy title so I'll explain. I bought this TV and was told that at some point it started turning itself off after being on for a while. Supposedly, it did this for a couple months and then just wouldn't come on at all anymore. So, I was thinking thermal shutdown. Probably some part of the power supply overheating. So, I bring the TV home, open it up and don't see any physical signs of component failure. I plug it in, and its not supposed to work, but it does. Now it did seem like it took a minute to turn on, but it wasn't supposed to turn on at all. I expected it to shut down after a few minutes but it didn't. I just watched the Hunger Games on it and it never cut off even once. I did have the back off so maybe that allowed the heat to dissipate. That still doesn't explain why it came on when it wasn't supposed to though. I can't diagnose this TV if its not acting up. So, how can I force this TV to act up? Also, the picture quality seems really poor. Is that normal for this TV?

[Caleb]

You can use a hairdryer on each board if you suspect heat stress.

[lookimback]

I don't have a hairdryer but could probably use my rework station's heat wand. What temp though? 100, 120?

[Caleb]

I would start pretty low as it was shutting off with the case on, you shouldnt need much of a differential to get it to act up.

[lookimback]

OK. So basically what's probably happening is, as something heats up, which causes it to expand, contact points within the faulty component separate and the TV shuts down. Then, with the TV off for a minute, the component cools and contact is restored. Am I correct on that? If so, then I should be able to identify the faulty component fairly easily by heating each one individually for a few seconds. And it shouldn't take much heat at all.

[lookimback]

I think this is it. I heated the power supply board, starting at 100° and nothing happened. Then I turned the heat up to 200° but held the heat gun back about 8". As I was heating the area where the bridge rectifier is (arrow in pic) this resistor located on the other side of the board (location circled in pic) arced and TV shut off. Wouldn't turn back on after cooling. Resistor code is brown, green, silver, gold, green. That makes it 0.15 ohms 5%. Testing with it removed from board its 0.3 ohms. I don't know how to determine wattage but this thing is kind of big. Its about 5/8" long. 3/16" diameter.

[Mrx3750]

Probably a 1 watt, but throw a 2 watt in to be on the safe side.

[lookimback]

Thanks for the quick reply. I have a Mouser order I need to put in tonight and was hoping I would get an answer so I could add the resistor in. I try to order parts for as many TVs as possible to cut down on shipping costs. I just hope this is the problem and not caused by me. The part of the board I was heating was about 3 1/2" away and not even in line with the heat wand. I did have the plate that screws to the top of the heat sinks in place at the time. I guess that transfered the heat.

[budm]

"Testing with it removed from board its 0.3 ohms" You reading the resistance value and the the probe's wires resistance, so 0.3 Ohms reading is OK, but it sounds to me you may have bad solder joints so that is why it was arcing, you may want to inspect the solder joints real well, look small ring around the joints, for examples: http://s807.photobucket.com/user/bud...?sort=3&page=1
By the way, make sure all the board mounting screws are tight since the circuits use the chassis for the ground connections. BTW, any one worked on this TV before, do not want to get another surprise.

[lookimback]

If you look closely at the pic you will see the resistor has spiral marks from it getting hot. Also 2 places within those marks where the ceramic (or whatever it is) came off. It was the middle of the resistor where I saw the arc.

[budm]

"It was the middle of the resistor where I saw the arc" OK, from the resistor body, so you may have found the problem then, it is MOX (Metal Oxide) Flame proof resistor. When you look at Mouser, it will give you the dimensions which you can use to match the one you have.

[lookimback]

Thank you. I was wondering if the dimensions could be used for determining proper replacement.

[lookimback]

Replaced the resistor but nothing happened. Checked fuse. Fuse blown. Replaced fuse. Fuse blew. I think problem is bridge rectifier. May be shorted. The 2nd, 3rd, and 4th terminals have 0 ohms between them. That would be the 2 AC terminals and the DC negative terminal. Reversing polarity gets same result. That's where I was heating the board too. Maybe I cooked it. Oops.

Edit: part number is D10XB60. Digikey doesn't have it. Mouser has similar but on order. Nothing in stock. Any suggestions on substitute?

[lookimback]

Finally got around to finishing this one. I replaced the bridge rectifier. Original part was no longer available so I had to go by the specs for it and find a substitute. The new one is a D3SB60-7000. All its specs are exactly the same so it should be fine. The original shorted while I was heating the board. Actually, I think maybe it was the problem all along though. I hadn't gotten it that hot when it shorted. Might be another issue though. I left it on when I went to sleep. It was on antenna with good strong digital signal. When I woke up it was blue screen saying no signal. Every channel same. I powered it off and back on and its been fine since. Got my fingers crossed.

[mntegra01]

I am having the same problem with my TV. Everything is fine until I put a cover on it. Once the cover is on it will shut down and return with blue LED standby light on. I can turn it back on in five minutes and it works great again. If I turn ceiling fan on it will cool the back of unit with fan blowing up, tv close to the wall in a small room. It works for hours. I had the cover off the back and it worked great for at least 5 hours. I was thinking of just adding a computer fan to the back and pull the heat out quicker, but I would rather fix the problem rather than bandaid it. I assumed it was a power supply problem since it was shutting off, so I never looked deeper into the problem. Always seemed fine without cover so I put it all back together. I'm getting tired of picking up this 100 pound tv and taking it apart.

[lookimback]

I was quite new to this when I was working on mine. I made a lot of mistakes. Never did figure out the problem, but it was definitely something with the power supply.

[mntegra01]

Encouraging to hear, lol. Tonight without any cooling added to the unit, mine went crazy started buzzing like a snowy picture and a scrambled picture and lots of green in picture. Guess its time to open it up again. But, same fix, turn ceiling fan on and works for hours.

[lookimback]

Mine never had any picture issues. I was able to determine the power supply as the problem by disconnecting the PS_on signal from the main, and then on the power supply, using a 5k resistor to connect PS_on to 5v stby. Then, when the problem resurfaced, I pin tested the PS connectors. There were voltages missing, though I don't remember what they were now.

[nomoresonys]

I think a lot of the back covers were poorly designed to let heat out, on my phillips 47 in. after recapping inverter board, I drilled a bunch of one inch holes to let the heat out, been working fine over a year now.