How to fix a CRT TV that shuts off when hot

A common problem with some CRT TVs is that they shut off by themselves after a few seconds or minutes of operation. This can be very annoying and frustrating, especially if you want to watch your favorite show or movie. What causes this problem and how can you fix it?

One of the possible causes of this problem is a faulty PTC thermistor for degaussing timing. A PTC thermistor is a component that controls the duration and intensity of the degaussing process. Degaussing is necessary to remove any residual magnetism from the picture tube, which can affect the picture quality and color purity. However, if the PTC thermistor is defective, it may overheat and trigger a protection circuit that shuts off the TV.

A PTC thermistor for degaussing timing usually has three pins and is located near the socket of degaussing coil, which is a large loop of wire around the picture tube. The degaussing coil is the actual device that generates a strong alternating magnetic field for degaussing. You can identify the PTC thermistor by its plastic case, which may have markings such as “PTC” or a catalog number. You can also use a multi meter to measure its resistance, which should be low when cold and high when hot.

To fix this problem, you need to replace the PTC thermistor with a new one of the same type and rating. You can find the specifications and ordering codes of different PTC thermistors for degaussing timing in the web search results I found for you . You can also check the replaced catalog numbers in case your original PTC thermistor is obsolete.

To replace the PTC thermistor, you need to follow these steps:

    Unplug the TV from the power outlet and wait for at least 30 minutes to let the high voltage inside the TV discharge.
    Remove the back cover of the TV and locate the PTC thermistor near the degaussing coil.
    De-solder the three pins of the PTC thermistor from the circuit board and remove it from the case.
    Solder a new PTC thermistor of the same type and rating in its place, making sure to align the pins correctly.
    Reassemble the TV and plug it in. Turn it on and check if the problem is solved.

If replacing the PTC thermistor does not solve the problem, there may be other causes such as bad capacitors, faulty solder joints, or defective components in the power supply or horizontal output stage. 

 tldr
replace ptc if it burn