Electrical Question about television set....

[Nick]

Hey guys, I have a question on a television. I have a small 13 inch TV/VCR combo and the thing is acting funny. The tv will turn on normally but the tube will cut off, leaving you with just audio. If you turn it off and on over and over again it will evetually stay on. In fact, from there the tv works great...it will work until you turn it off again. Now, I am suspecting there is a circuit or relay that controls the power to the tv tube and it is malfunctioning. I do not suspect the tube itself because like i said, it works fine once you get it warmed up. Does anyone have any experience with tvs, or does anyone have any idea what I can look for when I take it apart?? I am a computer/electrical engineering student so I am very familiar with circuitry but I was hoping someone out there could help me out with a shortcut to the problem.

Thanks,
Nick

 

[ussrover]

1. be very careful the CRT (picture tube) can hold a charge for upto
a year!!!!

2. sounds like there is a cold solder joint in the HIGH VOLTAGE section

3. using a solder (pencil or gun) heat the joints in that section and
apply a small amount of rosin-core solder to joints

hope that helps

when in doubt have a tv repairman do the work as they are qualified

 

[kamiam]

ussrover is correct about a bad connection usually this type of problem is a bad connection on the crt(pix tube) heater voltage circuit which is found on the 'flyback" transformer. this device developes several power supply voltages needed for the operation of the TV, amongst others it developes the heater voltages necessary for the pix tube to show a pix along w/the hi-voltage supplied to the crt anode (for your set its about 18 KV so be careful and dont remove the thick single wire attached to the pix tube)another place to check for bad connections (if it is a loss of heater voltage)is on the crt neck board.thats where the heater voltages enter the crt

 

[Nick]

Thanks guys, I'll check it out and see what I can find. I am some what apprehensive about it so I might just take it to a repair place, then again it may be just cheaper to buy a new one than have it repaired.


thanks,
nick

 

[Tiger]

Good idea.

If you do try to fix it, Unplug it first!
TV's develop voltages that will kill you if you mess up.

 

[UG]

Work with right hand, stand on right foot.

 

[Gustavus]

A quick and easy check you should do is to see if the filament in the CRT is heating when the picture is off. You should be able to see the glow in the neck of the CRT in a darkened room -- probably through the ventilation louvres on the set without even opening it up. If the glow disappears when the image does, you know what the problem is. I doubt this is the source of your problem, but it is so easy to rule out that you should do this first. If you have to remove the case to see the neck of the CRT most sets have a cheater switch to prevent people turning on the set with the case removed. Hold it closed and turn the set etc.

 

[kamiam]

Gus... that was the old tv's...nowadays there is no cutoff switch... I've been a tv/electronics tech for 20 years... if you can see the heater elements in the back of the set and it goes out then you've either lost just the heaters or something in the hi-voltage circuitry has failed... if you can "bang" on the set and it comes back to life then it is connection related...however even if it does not come back to life it still can be connection related however banging on it is a 1st step... also as someone suggested, there is generally not enough current in the circuitry(w/the exception of the main a/c power supply and the d/c regulator circuitry) to kill you...however you can still get a nasty jolt that will knock you back a few feet