Have LCD TV tech/repair questions.....

[blu_fuz]

I was going to try to fix a 37" Magnavox LCD for a friend of mine thinking that the capacitors on the power supply board were bad, but that doesn't seem to be the case and now I am lost for answers..... If I can't fix it they said to put it on epay for parts.


So basically, the sound and picture work great! BUT, the picture eventually gets dark blobs showing up in random places. Then once in awhile there is a square shape that is about 2"x2" floating around in different spots .


Not sure what to do next, capacitors are ok, if you have any ideas go ahead and throw them my way. I am thinking either the circuits are heating up too much (because some heat sincs are too hot to touch), or there are poor solder joints that are causing problems, or???


Good picture (will play for over an hour sometimes before the blotches show up):

Then the dark blotches show up but picture is still visible on other parts of the screen and sound is not effected:

Here are some pics of inside the back:

These heat sincs get reaaaaaaally hot on the power supply board:

 

[floyd]

you could take a pc cooling fan and mount it too the back panel of the tv just inside right on top of where the power supply board is.

 

[blu_fuz]

I'm not 100% that it's only because those parts seem hot, I only say that because I have turned on the tv and within a few minutes only (before it gets hot) the black blotches have shown up . And even with the temp being only 55* in my garage when I tested it, the sincs were hot .


I do have 6 PC cooling fans here, so that could be an option .

 

[Fatdog]

It could be a bad buffer board. You would need a specific one for that size / model, but this one is similar:

http://www.discount-merchant.com/BUFFER ... 109521.htm

 

[blu_fuz]

I did have that buffer board out and after looking up the part number on the board I was getting hits for the wrong brand and the wrong layout of the board .

Most boards have 2 or 3 ribbon wire connection points (like shown in your link), my board has 4 and even with the correct part number from the board, I still am only finding the wrong parts!!!!! :annoyed:


But, if I did find one - you think that could be the issue? Is their $100+ risk worth it for that board? Or just cut their losses and move on?

 

[Fatdog]

Joe, that board is for a 50" plasma TV. You have a 37" LCD, so it won't work for you. I only posted it as an example.

Just a thought, if you keep putting in the right part number for your TV and keep getting boards that look different from yours, perhaps the current board is incorrect and therefore giving you problems.

 

[blu_fuz]

Yeah, I understand that yours was just an example - I used your example to point out the examples of the ribbon connections I was finding that were not like mine but had the same part number on the board.

I have the right board in the TV, it just accidently crosses with other brands and they have the different ribbon wire connections

 

[Fatdog]

Now's the time too call Magnavox and tell them their TV is horse shiat!

 

[tshorba]

Shoot some of the IC's with freeze spray. This is how my old tech checked TV's out.

 

[blu_fuz]

Really? So I can shoot some cold compressed air at the ICs on the board when it is powered on and acting up?

 

[Superduper]

Really? So I can shoot some cold compressed air at the ICs on the board when it is powered on and acting up?

IF an item if failing due to overheating, you can spray some freeze spray on it to see if the symptoms subside. If yes, then you've found a problem semiconductor. Don't spray the **** out of everything. Most of the stuff that suffers from heat induced failures are semiconductors such as IC's, transistors, diodes, etc. BTW, a hot heatsink only confirms that it's doing it's job. It wouldn't be there if it didn't need to carry heat away. Many of the large IC's produce an enormous amount of heat.

As for showing pictures, one can't really tell what items are bad from a pic because a good working TV is liable to look exactly the same as a dead one. In other words, you can't tell simply by looking. However, the heat thing is a good observation so you can start there. But you know -- brand new 37" 1080p LCD's with all the latest features aren't all that expensive. So you be the judge as to whether it's worth throwing money at it. Cuz if it don't fix it, you would already be regretting going that route since it could be a down payment on the new one.

One last thing.... looking at the IC's, they are all high density SMD jobs. You WILL NOT be able to replace those using conventional soldering equipment. So even if you found which IC is bad after spending $10 on a can of freeze spray -- then what?

 

[blu_fuz]

^ I agree - I don't have the time to chase a problem like this unless it is obvious. I was hoping someone might have an answer, but it isn't that simple.

I will try the freeze spray since I have it here and can easily try that - probably going up on epay anyway.

 

[tshorba]

Freeze spray is different to compressed air

http://dicksmith.com.au/product/N1122/dse-freeze-spray
this is an example

It might help to find the fault, wait to the issue starts then spray 1 component at a time.

If the screen goes to normal you have found the faulty component

Dont forget on LCD/plasma/flat panel TV's the board will require replacement rather than a component.

 

[Superduper]

Dont forget on LCD/plasma/flat panel TV's the board will require replacement rather than a component.

Not necessarily. Depending in the chip and the skill and equipment (hot reflow) of the operator, they can certainly be replaced if the part is available.

 

[tshorba]

Dont forget on LCD/plasma/flat panel TV's the board will require replacement rather than a component.

Not necessarily. Depending in the chip and the skill and equipment (hot reflow) of the operator, they can certainly be replaced if the part is available.

Sorry I should have stated

"Dont forget, for the home DIY people, on LCD/plasma/flat panel TV's the board will require replacement rather than a component, this is due to SMT or surface mount technology. The equipment required and soldering skill of the operator is more adavanced than the standard that home users possess"

I did not mean to imply it is not possible, I think it is beyond the skills of 90% of people.

 

[blu_fuz]

This is the closest board I found by magnavox that has the 4 ribbon wire connection points, but it's the wrong part number and a little different layout :annoyed:
http://www.ebay.com/itm/Magnavox-37MF33 ... 1c1eb81a8e

 

[monchito]

i threw out a 42 jvc that was given too me being fixed 2 times and going bad again ,,it would turn on and display the jvc logo then shut off the board that was replaced was the power board but the backlight inverter board was known to go bad on this model also ..was only a year and a half old not many were sold because it was superceded by a different model.. i belive there were too many complains of failing boards and mostly all the same ones..... technology on lcd has been with us for a long time mostly computers but for some reason its still a bit of a baby when it comes to tv especialy large ones and i belive its mostly heat related .. its only been a few years since they introduced tv in the form of plasma and lcd ,,, failure on laptops were not as bad if u come to think about it and regular glass screens are still working after all these years even thou they no longer make them,, so i think in a few more years we should see a better improvement in the years to come ,,also a small note remember its really a lost if these lcd tv lasted more than 5 to 8 years thats why the trend of electronics lasting only a few years gone are those glorious 25 35 year electronics