My TV is broke... sometimes

[Jim Marnott]

I have a Hitachi 27" TV that I bought about 8 years ago. About 3 years ago I came home, turned it on and all I saw was a white line across the screen. The sound was perfect. It was about 2 days after my warranty ran out :( . I put it in the storage and bought a new one, which works fine.

About 1 year after the TV stopped working I was about to throw it out, but, just for fun, turned it on and lo and behold it was working fine. Wonderful, I put it in my bedroom and started watching.

Everything went well for several (2 or 3) months and then boom... back to the white line. So, back into the storage room it went.

Today, I was about to throw it out again, but turned it on "just to see" and it works again.

Now... can someone please help me figure out what is going on. Should I lug the thing back upstairs (it's darn heavy) or will it work again for only a month or two.

If it stops working again, then is the picture tube busted, as I was told? If so, then why does it work every year for a few months? If not, then what's the problem? Can I fix it at home (not all that handy with electronics but I do have a multimeter and I did once fix a CD player/mini-stereo)? If I can't, or shouldn't fix it at home, then what should it cost to get it repaired.

Thanks, Jim

[Tony Hwang]

[Jim Thompson]

The picture tube is NOT busted. The set has an intermittent vertical sweep circuit. Could be as simple as a cold solder joint.

Carefully take the set apart and look over the printed circuit board for cracks that might be breaking a trace.

If you can't find anything like that, *if you're skilled with a soldering iron*, carefully re-solder the whole board so that all the traces look shiny.

...Jim Thompson

[tnom]

The vertical section has a intermittent problem. Go to Radio Shack and get some long fiberglass or plastic tuning wands. The voltage inside the set is lethal, even when off and unplugged. If you are willing remove the cover, supply the power, and start poking around with the insulated tools. Maybe you will get lucky and find a loose connector or bad solder joint.

[Tony Hwang]

Hi, Simply just a long chop stick from Chinese restaurant will do the same. Another way is to use cold spray to pin point offending component. Tony

[Frogleg]

You're experienced with this? It sounds *wonderfully* logical for heat-related problems. I'd like to see more details on the procedure.

[BinaryBillThesailor]

That's one of the basic troubleshooting methods for finding intermittants. Anyone who works on electronics uses it. You can buy a can of freeze spray at any electronics distributor, or probably even at Radio Shack. Spray a small area at a time, and wait a few seconds. Usually, and experienced tech will spray known suspects or areas first, and perhaps even particular components that are commonly problematic. Usually not much sense in spraying the audio section for a video problem. In TV's, there are a few things that are very common, that are not hard to fix. One is cracked solder connections on the connections to the flyback transformer. The flyback is heavy, and over time, the pins that connect it to the circuit board develop ring cracks from stress. Another thing to check early on, when troubleshooting without a schematic is any component that is mounted to a heat sink. Things that get mounted to a heat sink are ones that run hot, work hard, and are most failure prone. The vertical drive transistor is one such component. The vertical drive circuit is basically the same thing as a mono audio amplifier circuit.

BB

[Tony Hwang]

Hi, I am retired EE whose schooling was in the days of vacuum tubes. Paid my tuition fixing TVs in old days. Most common failure in TV set is capacitor failure(heat sensitive). Being careful of lethal voltage inside TV, you give quick shot of spray onto suspected component. In this case vertical drive is suspect, so spray around that circuit. Most PCB has silk screened markings. When you heat the culprit, you'd know. Tony

[Doug]

BTW, Don't get that cold spray on the glass of the picture tube.... Big Bang theory..... :-)

Doug