Vizio VO47L inverters or Power supply

[dkelsey56436]

Hey guys,

Trying to repair this Vizio tv and after scouring the site and others as well, I'm confident that this is a common problem and points to the caps on the inverter boards, but I have what may be a basic question. Ill describe briefly the problem since its been talked about extensively, then my question.

Problem:
Intermittent back light flashing. Sometimes it starts immediately and other times it takes hours or never happens at all. I pulled it off the wall expecting to see bulging caps, but unless I'm missing something, all caps look good on all boards and I do not have an ESR meter yet to test them. My plan is to replace the caps on the inverters anyways unless someone steers me in another direction.

Question:
A transformer on the AC side (I believe) is making a slight audible buzz with a click - click - click very rapidly when the tv is on, even after removing completely both the slave and master inverters. This happens no matter what the back light is doing. What is this and is it contributing to my problem?

Link to the video of the sound (please turn up volume)
http://youtu.be/qUXgObsqR_I

Pictures of the caps (all same board since they all look similar)

[dkelsey56436]

Re: Vizio VO47L inverters or Power supply

Bump

[stj]

Re: Vizio VO47L inverters or Power supply

intermittent stuff is a bitch.
check the soldering on the psu.
if you can work out which pins on the invertor are the main power input then maybe fit a pair of wires that hang outside the case.
then put a resistor & led on them and when it starts flashing, see if the led is also flashing.

[budm]

Re: Vizio VO47L inverters or Power supply

Did you do close up inspection of the boards for any bad solder joints?
Do you have ESR meter to check those lytics caps on the inverter boards? You can try heating up those caps with hair dryer then power up the TV to see if the backlights will come on right away.
You should also monitor the 24VDC feeding the inverter, the BL_ON signal, ETC when it is working and when it does not work.

[dkelsey56436]

Re: Vizio VO47L inverters or Power supply

I have not been able to reproduce the flashing in the past few days to do any more voltage testing, but I do have the power supply removed and noticed that one leg of one of the transformers has no solder. Why would this be and do I need to solder this area?

[dkelsey56436]

Re: Vizio VO47L inverters or Power supply

And I did use a hair dryer and cannot get any reaction out of the back lights. The voltage on the 24v lines are are reading 23.7, which I assume is ok since the tv is working fine with these readings.

[bammbammfran]

Re: Vizio VO47L inverters or Power supply

I have not been able to reproduce the flashing in the past few days to do any more voltage testing, but I do have the power supply removed and noticed that one leg of one of the transformers has no solder. Why would this be and do I need to solder this area?

that pin is not being used in this instance

[dkelsey56436]

Re: Vizio VO47L inverters or Power supply

Thank you BammBamm. At this point, ill leave it on again for a while and see if the flashing starts. If not, I'll put it all back together and wait for it to become permanent instead of intermittent or wait until I get an ESR meter to do some further inspecting.

By the way, how could you tell this was not being used? The lack of any sign of previously applied solder to the joint?

[stj]

Re: Vizio VO47L inverters or Power supply

the soldering on that transformer is cracked.
i know you probably cant see it - but trust me!

[dkelsey56436]

Re: Vizio VO47L inverters or Power supply

So you think that it is possible that this transformer is heating up, losing solid connection and sending unstable power signals to the inverters? I could see that, but wouldn't cracked solder pose a much higher threat cold than hot? Things do expand when heated. Also, ive done a fair amount of soldering, and these all looked solid to me. I admit though that ive never soldered on a board though.

[stj]

Re: Vizio VO47L inverters or Power supply

shadow-rings in the foto.

oxides form in the crack-layer and after that expansion has little to do with it.
cracked solder is common on heavy or oscillating parts.

[dkelsey56436]

Re: Vizio VO47L inverters or Power supply

Wow, I see it now. Then I may have quite a bit of re-soldering to do since I noticed that in various places. I will certainly gain some experience on board work here. At this point with the TV being made in Dec. of 2007, is this going to be an ongoing issue with all heavy or oscillating parts?

[stj]

Re: Vizio VO47L inverters or Power supply

only coils oscillate.
but heavy parts put stress on the joints.
and also parts that are bolted to heatsinks can be under stress.