Emerson LTDN42V68US - No Pic/No Sound

[Snugglekins]

Hi all! I am having issues with my flat screen. The set is about 3 years old. I am not sure what happened (line surge, likely), but one day it began acting funny. When plugged in and turned off, the red LED in the bottom right corner would remain lit (not flashing). When I tried to turn the unit on, the light would turn blue and the backlight would come on. The backlight would then turn off after about 1-2 seconds, but the blue LED would remain lit. I would also not get any sound. I turned it on and off a few times, but the behavior repeated every time. I then completely unplugged the unit from the wall and let it sit for about 5 minutes. Upon plugging it back in and pressing the power button, the unit lit up and worked perfectly. It worked without issue for a couple more months before the problem resurfaced. Again, I was able to rectify it by completely de-powering it and then turning it back on. In all, it happened 2-4 times total before finally giving in completely. Now, it refuses to stay on even after power cycling it.

I have attached pics of the exposed unit and boards. After lurking the boards, I noticed that voltage regulators and power boards were typically chief suspects. I took the liberty of performing some voltage measurements and including them here.

N4
AZ1084S
-ADJE1
024JC0
pin 1 - 5.20V
pin 2 - 3.32V
pin 3 - 2.07V

N2
1117A
JCNC1Y
pin 1 - 5.25V
pin 2 - 3.32V
pin 3 - 2.06V
pin 4 (fat tab) - 3.30V

N5
(same as N2)
pin 1 - 3.32V
pin 2 - 1.25V
pin 3 - 0.00V
pin 4 - 1.25V {I double checked that I was not confusing the terminals}

N3
(same as N2)
pin 1 - 5.20V
pin 2 - 3.28V
pin 3 - 2.04V
pin 4 - 3.28V

On the power terminals, I took measurements on the different pins with the unit off then on to compare readings. Basically, there were no differences between on and off. Also, every pin read 0V except the S5V pins and the 16V pins. The S5V pins read 5.27V on and off & the 16V pins read ~17V on and off (though I noticed that the voltage kept climbing the longer I allowed the power to stay on. I eventually turned it off after reaching 17.5V.)

Any help you guys can offer would be greatly appreciated!

[Snugglekins]

Re: Emerson LTDN42V68US - No Pic/No Sound

Whoa guys, slow down! I can only go through so many replies at a time.... :\

So I was shopping around on ebay and found a seller offering a "full tuner lot". Replacement main board, PSU board, backlight inverter board, speakers, and IR sensor for $65. Guaranteed 100% working and the seller has a solid reputation. Figured even if this was overkill, it is still an awesome deal so I nabbed it. Should be here in ~1 week. I will post results after they arrive.

[selldoor]

Re: Emerson LTDN42V68US - No Pic/No Sound

Holidays - people have other things to do.
Sounds a bargain. I dont know much about tvs but VRs seem ok Adj are 1.25v above pin3. Perhaps try replacing the two small caps on the primary section of the power supply - one or both may be startup caps

[vinceroger69]

Re: Emerson LTDN42V68US - No Pic/No Sound

you can also try heating up the psu with a hair dryer etc for about 3 to four minutes then try powering the set up.

[Snugglekins]

Re: Emerson LTDN42V68US - No Pic/No Sound

you can also try heating up the psu with a hair dryer etc for about 3 to four minutes then try powering the set up.

I will try that. Just curious but what would be the point of this?

[selldoor]

Re: Emerson LTDN42V68US - No Pic/No Sound

Essential tool!

Some faults are caused by small cracks in the solder- heating can expand the
solder and close the crack completing the circuit temporarily. Do it in the dark and you can sometimes see a spark.

In your case where we suspect worn out caps it causes the ESR to drop and
the function of the cap is improved, again it is only temporary, but if a cap is failing it can just mnake the difference between it working and not.

[Snugglekins]

Re: Emerson LTDN42V68US - No Pic/No Sound

Ah. Good to know. I tried it, but no joy. Still awaiting the new parts. I will install them piecewise starting with the power board to see which one is the culprit.

[Snugglekins]

Re: Emerson LTDN42V68US - No Pic/No Sound

Ok sorry for the belated response. Spring semester just began so things got hectic for a bit. New parts came in. Looked them all over and they seemed to be undamaged. Started with the power board since it was the most likely suspect. After about 5 minutes of screw turning and plug... plugging... the unit fired right up and stayed that way. It has been over 24 hours and it has shown no signs of faltering. ~$75 after shipping and about 15 minutes of work and the unit is working like new (and I have some spare parts for down the road!).

Now that the initial problem has been solved, I would be interested in trying to address the fault in the power board (if only for an educational purpose). Any input on what I should start with and how to go about it?

[multimeter]

Re: Emerson LTDN42V68US - No Pic/No Sound

the fault your describing ,sounds a hell of a lot like cold solder joints to me.

look for ring cracks around the legs of components with a strong magnifier on silk screen side