weird problems with TV

Rouslan N. · Guest

I have a LXI series color TV. It worked fine until one day the screen wobbled back and forth, and every time I tapped the case the screen went like crazy, and there was a sound inside like sparks.

I tried moving the TV and after the wobbling and noises, the picture turned into a white dot, and wobbled back and forth ~0.5 sec until blacking out.

I tried repowering it, but it makes this weird squeaking noise inside when I do it quickly. It works, however after ~30 sec of being unplugged.

Does anyone know what the problem could be?

Guest · Posted: Thu May 18, 2006 5:53 pm Post subject:

It could be the B+ filter capacitor is open circuit and the supply is unable to regulate. If you continue to switch it on like this you could destroy expensive parts inside. Are you able to test the electrolytics and look for broken solder joints?

Rouslan N. · Guest

I could not really find any bad solder joints from a quick inspection (I will take the whole power supply board out later).

-Is the B+ filter capacitor the biggest one inside the TV?
-Do you think it is a problem with solder joints rather than the capacitor?-the problem varied (before I knew it could damage the parts) when I tapped\moved the TV physically
-I read in a switching power supply repair manual that I should put a dummy load across the outputs to avoid damage while repairing. Should I really do this?
-Out of curiousity, what was that squeaking noise inside?

Guest · Posted: Wed May 31, 2006 7:42 pm Post subject:

The biggest capacitor is usually the mains capacitor. Beware of it.
The B+ capacitor may be the second to biggest capacitor.
Bad solder joints are hard to see, did you use a magnifier or gently wiggle the components while looking at the joint?
The problem could be a capacitor, solderjoint or any number of things.
If you run a switching powersupply with no load it will blow up. If you disconnect it for repair, use a dummy load.
The sound is either the sound of the transistor switching on and off or the sound of the windings in the transformer. (or maybe both)

Guest · Posted: Wed May 31, 2006 8:05 pm Post subject:

All CRT's emit X-rays. It was more of a problem with older sets. It is your job as the service person to make sure the high voltage is not excessive and within specification.
The metal casing and the back of the CRT (the black paint) are the ground for the 30 000 volts. Do not touch it and the big thick wire. (always keep one hand in your pocket)
You MIGHT have bad B+ regulation. Solder your meter leads across the B+ capacitor and measure it if you are game to switch it on again.
Use a long thin stick (dowling or electrical insulating material) to prod the components, it will put you closer to the problem than tapping the case.

Here is a site you may want to read.

http://www.repairfaq.org/sam/safety.htm

Let us know how you go.