Friday, June 24, 2011

2011.06.24 Friday - How to fix a LN-T4066F

Mmm sleeping in.

My sister brought over a TV to fix. Apparently it is having the same problems as my brother's Samsung.

***If you are following the steps I have followed, I urge you to use caution. Capacitors are electronic devices designed to store electrical charge. There is possibility of electrical shock, injury, or even death. I take no responsibility for your actions.***

First thing I did was test out the TV. I plugged it in, and the red standby LED came on without a problem. I pushed (or touched) the power button (sensor) to turn on the TV; it played the start-up jingle and the white glowing area in the center below the screen came on. The screen and backlight did not turn on. Actually, the first time it played the startup jingle, it was kinda static and fuzzy sounding. After about 5-10 seconds the startup jingle would play again, but sound less fuzzy. This repeated about 10 or 15 times, then the screen finally came on.

I let the TV stay on for a bit, plugged in a few HD sources to see if it would display everything. Once it booted up everything was fine. I then turned off the TV (to standby) and waited a minute or so. Then upon turning it on again everything booted up just fine, no multi-jingle. I guess whatever residual charge or warming up helped the TV boot.

I then unplugged the TV to let all the capacitors drain and to let everything cool off. Some hours later I plugged it back in, and unfortunately the problem resurfaced - troubled startup.

After unplugging the TV and waiting a few more hours to let any residual charges dissipate, I laid the TV face down on my bed (ideally you would want to use something soft and even in pressure), took out the four screws for the stand, then the 12 or so screws that held on the back plastic cover.

I took a picture and made the unimportant areas black/white, and the power supply board colurful. Here's what it looks like:

Now here is a close up of that power supply board, with the area of interest in color and the rest black/white:

Now here are two close ups of the capacitors in the area of interest for us. There are 7 blue electrolytic capacitors in the middle of the frame, 5 of them are taller and 2 are smaller. The problem is that some of these capacitors are bulging. That is a sign of being pushed beyond the rated specs, usually leaning towards total failure. Electrolytic capacitors operating outside their range start to build up internal pressure; as a safety measure, most capacitors will either expand or leak gases instead of just exploding.

So backing up a little: On the power supply board, there are two cables on the left going to the backlight/CFL, another cable on the left that I assume controls the level of backlighting, two cables on the right going to the main logic board, and two connectors on the bottom right that are coming in from wall power. I removed all of these connectors without any issue. Some have clasps to hold themselves in. There were about 5-7 screws holding down the power supply board; these need to be removed. Once those were out, the board slides right off, and now I have easy access to both sides of the circuit board.

To remedy our situation, we are going to be replacing these capacitors with something of the same capacitance (rated in Farads, or in our case micro-Farads) and a voltage rating of something equal or greater. I personally like to err on the side of caution and go for something with a bigger voltage because obviously the capacitors with this rating are failing in this circuit. Going with a bigger voltage rating just means the capacitor is capable of sustaining a higher potential difference between the plates, before failing. I went to Fry's electronics for capacitors. It is not the greatest for selection, but it is available now. Surprisingly, they had a sign up saying common capacitor values to put in flat panel TVs. I thought it was funny because they are also selling said flat panel TVs on the other side of the store.

Previous Capacitor Layout
CB850 : 1000uF 10V
CM852 : 2200uF 10V
CM853 : 2200uF 10V
CM876 : 1000uF 25V
CM880 : 1000uF 25V

Revised Capacitor Layout
CB850 : 1000uF 16V
CM852 : 2200uF 25V
CM853 : 2200uF 25V
CM876 : 1000uF 50V
CM880 : 1000uF 50V

After some quick desoldering and resoldering, cutting a few leads, everything was swapped out. If you are using a soldering iron for the first time, I highly suggest practicing on something of lesser value first. Soldering irons get very hot. Again, I take no responsibility for your actions, just describing what I did. Another thing worth mentioning is the electrolytic capacitors have a polarity, meaning they are OK being plugged in one way, but will completely fail if plugged in backwards. Take note of the orientation before swapping them out. If you happen to forget which way they go, look at other capacitors as reference on the circuit board, there are markings for the negative terminal.

I put the board and connectors back, screwed everything down and went ahead and tried plugging it in. The standby LED came on, then I powered it on... success on the first try. I then hooked it up to some sources and let it run for a few hours to see if there would be any hiccups. After a few sessions, I have yet to reproduce the booting problem. SWEET.


Over the course of the day, I worked on a TV, watched Habs fix a computer monitor, ate chik-fil-a for lunch, played games on a 40" screen, and cooked myself an awesome pesto-pasta and ribeye steak dinner. A++, would do again.


Anonymous said...

Thanks for this write-up. I just finished the capacitor swap on my LN-T4066F (following your guide) and it fired right up when I plugged it back in. It formerly had a similar issue of 3 cycles of on-off while starting up "cold" and also the random start-up magenta pixels that would go away on re-start.

I haven't had any time to test it at length, but I'm pretty confident it's going to hold up. Well worth the small amount of money and my time.

Thanks again. Cheers,


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