Entertainment Center: TVs, Stereos, VCRs and DVDs - TV will not turn off completely

Model #SMO953X Zenith portable TV- when I turn off the TV , the sound and picture correctly disappears , but a bright blue
flicker of light ,which rapidly collapses , continues to cycle until I pull the electric cord from the wall outlet. What is going on ? How do I remedy ?

Good Morning, stilllearning23:

Rather than go into a lengthy explanation on this problem, pop over to this website and read Chapter 28.27.
http://an.hitchcock.org/repairfaq/REPAIR/F_tvfaq.html

This is not an uncommon problem.


Smokey ;)

Thank you for the tidbit. I am really a novice at TV repair , with some basic understandsing of household electricity . The section that I stiudied re : Tv not turning off resembles my issue somewhat . What seems to differ is that when I plug the set into the wall outlet , the cycle of a full screen flash followed by its collapse on the screen starts immediately -- even though I did not turn on the " On" power switch . Is this the same issue described in that section or is it another issue ?

Good Afternoon, stilllearning:

Just a quick question:
How much time has elapsed between the time you unplug the set and plug it back in? What I am trying to determine is if this "flash" happens to a cold TV that has been off for hours.

That puts us back into another arena if this is what is happening.

Smokey ;)

The TV might be off all night unplugged and the cycle will start immediately upon plugging it into the wall .

Good Morning, stilllearning:

Well, that sheds a new light on the problem. This means that the television set is never actually powering down totally.

In these units, you have an electronic on-off switch and most sets use a device called a Triac. In the old days, you had a mechanical switch and when it failed, you just put in a new one.
But, with remote control, they have changed to an electronic switch which can be keyed on and off with the remote.

Unfortunately, the electronic switch will short out once in a while
leaving a direct connection from the cord to the low voltage power supply. This is rare, though, because the units are usually
very reliable.

But, it's time for the technician on this one. A set that is not
powering down becomes a fire hazard and I suggest you continue to unplug the beast when you are not watching it.

And, if the set has some years on it, it might be a time to take the family TV shopping for Christmas. I don't recommend putting a lot of money into an older set. New ones are not that expensive anymore. This repair could cost a couple of hundred dollars (mostly labor charges). That would make a nice down payment on a new set.

Smokey ;)

Thank you for the analysis. I never heard of Thyristor. Is this a resistor which changes its resistance properties when another parameter changes , like a thermistor ( resistance will change as temperature changes) in a stove oven meat thermometer ? Is it possible for a diyselfer to swap in a new one ? Where /what to obtain ?

How old is this television?

I believe that the TV was purchased about 5-7 years ago .

Good Morning, stilllearning:
Old Smokey is having brain malfunctions, I guess. It's not a Thyristor. It's a triac. The triac is a gated electronic switch that
has probably shorted out in your set.

Man, this alzheimers is getting bad.


Smokey ;)

Since your previous posts, I have been doing some reading about the fundamental characteristics if thyristors, diacs, triacs. Now , at least I understand their function / anatomy. If the triac were shorted, can I identify and replace this myself ?

If a triac does exist in the set, and it is shorted, than you most certainly can replace it.
Firstly, you would need to identify it. A triac is basically an electronic switch which switches on and off Alternating Currents.
They come in random packages but almost always have 3 pins. If one does exist, then you'll find it near the area of where the A/C cord comes in to the set.

That's encouraging information . I'll try to take a look this weekend . Any advice . suggestions ,sources ?

Good morning, stilllearning:

If you decide to tackle this repair, yourself, then I would suggest you pick up a service diagram on the unit. These are available from either Sams Photofacts on the web at
http://www.samswebsite.com/
or (another good source) is Union Electronics on the web at
http://www.unionel.com

Union Electronics is a good source for Zenith repair parts. It seems they stock them when others don't.

As for the Sams Photofacts, it contains circuit diagrams, parts
locations, adjustment procedures, etc. for the doityourself person.
The cost of the diagram and the parts should be a lot less than
the costs at the repair shop.


Smokey ;)