identifing a component need help - Page 1
Forum section: electronics / beginners

author: Alberto-Elaria
author_rank: Newbie
timestamp: August 16, 2011, 05:30:00 pm
content: hi guys this is my first topic, i am organizing my component cabinet i came across one component but i am not sure what ist.i think its a resistor but not sure i took it out from a sony tv board. i put a link in YouTube trying to see if any one can recognize it and help me any way the link below.

author: KJ6EAD
author_rank: Contributor
timestamp: August 16, 2011, 05:37:39 pm
content: It's a dual element thermistor for the degauss circuit in the TV. If you gently remove the lid by prying in the notch on top, you can see the disk-shaped elements positioned between the contacts.

author: Alberto-Elaria
author_rank: Newbie
timestamp: August 16, 2011, 09:00:31 pm
content: Quote from: KJ6EAD on August 16, 2011, 05:37:39 pmthanks mate.. i will label it as thermistor

author: tekfan
author_rank: Frequent Contributor
timestamp: August 17, 2011, 08:48:20 pm
content: It should also be pointed out that this is a PTC (positive temperature coefficient) thermistor. Meaning that its resistance increases as its temperature increases.

author: Fraser
author_rank: Super Contributor
timestamp: August 28, 2011, 04:13:51 pm
content: In the UK TV industry these are known as "Posistors" and, as has been stated, are used in the Degauss circuit.When a Colour CRT TV is switched on, one of these is in series with the Degauss coil around the CRT face plate. A large AC current flows from the mains supply via the Posistor and into the coil and so Degausses the CRT shadow mask. This process prevents colour contamination of the image due to unwanted magnetism of the shadowmask. The posistor is essential to control the current passing into the coil or else there would be a nasty overheat in the coil ! These components often fail open circuit in CRT TV's and the user then complains of strange colour casts on part of the picture (mangetic contamination of the shadow mask). Magnetic contamination can occur naturally due to the earths magnetic field or man made sources such as Hi-Fi speakers next to the TV.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 28, 2011, 05:14:14 pm
content: The PTC is actually an essential part of the operation of the degauss circuit, not just prevention of overheating. It provides a large initial current, dropping over several cycles to a small value. This produces a field that is a strongly damped sine wave, which is critical to the degausing behavior.

author: IanB
author_rank: Super Contributor
timestamp: August 28, 2011, 05:48:44 pm
content: Quote from: Aurora on August 28, 2011, 04:13:51 pmQuote from: ejeffrey on August 28, 2011, 05:14:14 pmAll of which explains, presumably, why CRT televisions make that loud "BRRTTT" noise when you switch them on...

author: Fraser
author_rank: Super Contributor
timestamp: August 28, 2011, 10:18:13 pm
content: Correct... but sadly with the avent of LCD TV & monitors, that sound will quickly become something from the past.I still enjoy using and maintaining Valve equipment but TV has firmly moved into the purely semiconductor age where degausing is no longer required.