Tag Archives: tv

TV Goes Flaky a Few Minutes after Warming Up

Our TV had been working fine for years, but then the display started going weird after a few minutes of warmup. General rule for TV’s and Monitors that do this: look for bad capacitors.

marginal screen
It looks kind of like Van Gogh’s “Starry Night,” but actually, black and white vertical stripes are flickering across the screen.
bad screen
After a few minutes, the TV gives up and looks like this.
chassis screws
Okay, let’s open it up. In the back of the TV, look for arrows on the case, marking the screws that need to be removed. There were like 12 or so screws, most on the edge but some in the middle.
open case
The back of the TV is off. The light colored board in the middle is the power supply – usually a separate board, and easy to remove.
some swollen capacitors
Electrolytic capacitors have a cross pattern on top, which makes it easier to spot swollen ones. There are 3 swollen ones I can see to the right of the aluminum heat sink. The second from the bottom doesn’t look swollen, but I’ll remove it anyway, just to check.

I’m skipping the detail of unplugging all the connectors from the power supply board and removing it.

list of suspect capacitors
Before removing the capacitors, I’ll make a list of the size and location of each, to make sure I don’t forget what goes where.

The suspect capacitors were all unsoldered from the board.

2200 uF reads 241 uF
An experienced tech would simply replace the swollen caps by virtue of their being swollen. But since I had a meter, I measured them. The 3 swollen caps all had only about 5-10% of their rated value. The non-swollen one was supposed to be 1000 uF, and was 925 or so – considered good.
capacitor replacements
In each pair, the capacitor on the left is the original, and the one on the right is the replacement from my parts box. In general, it’s okay to replace capacitors with higher voltage or temperature ratings (but NEVER lower). In power supply applications, it’s also okay to replace with higher capacitance. Truth be told, I’ve found that I can even replace a capacitor with something about half the value and it works fine – handy if I’m short on a particular size capacitor. The cap at bottom right measured all right, so I’m going to put it back. Many technicians would advise changing all the caps in the vicinity, on the theory that they all should be about to go. But I say waste not, want not, and I have time to go in there again if the last one goes bad.
good screen
That’s more like it.