About Posistor (Positive Temperature Coeeficient-PTC)
If you have been in the CRT Monitor and TV repair, i’m sure that you must have come across the square black plastic with two or three legs at the input AC area just after the EMI/RFI Filter circuit. That component is posistor (PTC) and the function is to control the degauss. When you switch On the CRT Monitor or Television, the PTC resistor is cold and low resistance. When heated, it becomes very high resistance and turns off the degauss coil but gradually – the current ramps down to zero rather than being abruptly cut off.
Usually when this posistor have problem, the degauss function would not work and many times it would blow up the main fuse (but the bridge rectifier was okay). It is quite hard to test the posistor and sometimes when it has problem you could hear some loosen parts in it when you shake the posistor. Since this part is easily available from electronic stores and from junk Monitor or TV, i would usually make a direct replacement and retest the set again.
Tips: If you can’t demagnetize the CRT tube that have color patches even with the help of a degausser (demagnetizer) then chances is high the tube may have problem. If the color turned back to normal after using the degausser, then look for dry joints in the degaussing circuit and replace the posistor and test it out again.
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76 Comments
Bambang Suhardjo
November 29, 2010 at 3:09 pm
About PTC what's ?
admin
November 30, 2010 at 7:10 am
Hi Bambang,
What is your question?
Jestine
Dranreb Adviento
October 14, 2016 at 6:54 am
sir is there a difference between 2 and 3 pin posistor? the tv that i am trying to fix originally has a 3 pin posistor then i tried to replace it with 2 pin only and still doesnt have any result the problem was the demagnetizer before the original posistor with 3 pins were become so hot when i turn on the tv but then i use the 2 pins its cold
Jestine Yong
October 20, 2016 at 9:12 pm
Hi Dranreb,
Yes there is a different between 2 and 3 legs posistor. A 3 legged PTC will permits the residual current to reduce further. The best you put back 3 legs posistor.
Jestine
Emerson P. Mante
November 6, 2012 at 10:36 pm
Hi Jestine,
if the posistor is defective is it possible that the TV set will not work or no power at all?
Thank you,
Emerson
Jestine Yong
November 7, 2012 at 9:22 pm
Hi Emerson,
If the posistor is open circuit the tv can't have the degauss mode. If the posistor is shorted it will blow the main fuse bu the bridge rectifier is good.
Jestine
filjohn collamat
July 19, 2014 at 9:56 am
ahh ok sir tnx for the tips,,i encounter already that kind of problem in KOLIN KCP-2190 model,, question sir but if ever sir i dont have a new or good posistor then im going to hang it up or no posistor can be replcd it is ok sir?
Jestine Yong
July 19, 2014 at 10:01 am
Without posistor the color impurity can't be removed unless if you have a demagnetizer. You can easily find one from junk board.
Jestine
Smulik mops
March 16, 2014 at 7:46 am
Hie pass me here,am a qualified electrical technician with close to 20years in machineries and controls,about 7years in tvs,and smps,but not fully in tvs,so a have replaced my telefunken tv flyback tx,after a year it doesn't switch on until i adjust focus & g2 (2 nobs)on flyback and is almost 4months with ths prob,i wanted to substitute flyback what could be the problem here,i have tryed with new hot and surge protector but stil no ans?thaks guys
Jestine Yong
March 17, 2014 at 9:38 am
HI Smuliks,
Just to verify your question again- Do you mean you want to look for a substitution of the flyback?
Jestine
Kath
January 11, 2015 at 2:45 pm
Hi there Im an ECE student and I just want to know if Posistor can also be a heat sink ??
admin
January 13, 2015 at 6:50 am
HI Kath,
Posistor is not a heatsink.
Jestine
harley
April 14, 2015 at 5:38 am
hello thank you for your article, could you answer, for TV's degauss circuit, why do some PTC's have 2 legs and some have 3 legs?
Jestine Yong
April 14, 2015 at 9:52 pm
Hi Harley,
The function of PTC thermistor is to degauss the shadow mask of colour picture tube by reducing the alternating current flowing through the degaussing coil within a short period of time. A big difference between inrush current and residual current is crucial for good degaussing. A 3 legged PTC will permits the residual current to reduce further.
Jestine
harley
April 15, 2015 at 2:16 am
that's very interesting thank you for your excellent response.
sandeep
June 14, 2015 at 5:03 pm
Sir I have problem I have a crt tv when I switch on the tv play green I can see the image but a lot green colour what the problem sir?
Jestine Yong
June 15, 2015 at 1:07 pm
HI Sandeep,
I suggest that you check on the green color circuitry in the crt board. You can also compare the blue and the red signal.
Jestine
sandeep
July 17, 2015 at 1:58 pm
what can cause this green colour problem
Jestine Yong
July 20, 2015 at 10:58 am
Hi Sandeep,
What green colour you are referring to?
Jestine
sandeep
July 23, 2015 at 2:14 am
I fix it sir one of the three resistance in the pcb board have drop i change it work with no problem thx for the help
sandeep
July 23, 2015 at 2:22 am
hi sir i have a sony trinitron when plug it power on it make hissing noise then no picture stanby light blink 1 time what's the problem u can help me sir
Jestine Yong
July 24, 2015 at 8:43 pm
HI Sandeep,
Have you checked if the output voltages from the power supply giving the right and stable voltages or not?
Jestine
christopher
January 4, 2016 at 10:31 pm
Fantastic comments and brilliant answers. Thanks Mr J. Yong.
Anil
May 3, 2016 at 1:12 am
Hello sir ,
I was facing the same problem so I change the ptc.All is ok but while increasing contrast screen becomes reddish & decreasing it going greenish but picture is ok.
what would be the problem ...
Jestine Yong
May 4, 2016 at 8:09 am
Hi Anil,
It could be due to weak picture tube or the color section have problem. If the OSD menu is good then it is not related to picture tube.
Jestine
ARIJIT DAS
September 6, 2016 at 2:37 pm
HI JESTINE SIR, I AM ELECTRONICS STUDENT , I HAVE COLOUR GREEN AND PURPLE PATCHES TOP OF MY LG CRT TV, IS THIS PROSISTOR PROBLEM??
Jestine Yong
September 6, 2016 at 11:02 pm
Hi Arijit,
If the color patches can go away with the help of a demagnetizer then the problem is in the posistor.
Jestine
Hari P
October 2, 2016 at 4:33 pm
1)does posistor heat up even when the circuit is open ?
2)my sony crt shows yellowish color and red color is blackish but when i increase color intensity red can be seen blue and green are okay but red is not ok.
Jestine Yong
October 5, 2016 at 9:54 am
Hi Hari,
If the circuit is open the posistor would not heat up. The color problem try check for any bad E-caps in the CRT board. If possible use ESR meter. I have not tried using the led to check on the current flow to the posistor. If you have the time you can do the test and remember to connect a resistor in series with the LED.
Jestine
Hari P
October 3, 2016 at 8:13 pm
3) can we check tge wirki6of posistor by connecting a small led bulb to degauss coil output connection, so we can figure out weather current is flowing from posistor to the output?
Thanks
Hari P
October 6, 2016 at 10:26 pm
one more question sir,
i have noticed that now there is no static on crt glass when we bring hand near crt front glass no hair is attracted towards the glass of crt, but whereas i have always noticed static in every crt tv, so why this sony wega is not attracting hair ?
Jestine Yong
October 10, 2016 at 3:19 pm
Hi Hari,
Is the Sony Wega TV working?
Jestine
Hari P
October 11, 2016 at 8:27 am
yes tv has no problem in working but the led blinks 5 times continuously since tv is turned on.
the vertical ic was replaced a year back and now again vertical ic has problem, there are lot of horizontal lines when we turned on and disappear after few minutes and picture becomes clear.
Hari P
October 11, 2016 at 3:22 pm
https://drive.google.com/file/d/0B4HwoUr6x54gdnZXTFY0RzlyaWc/view?usp=docslist_api
please see the image in the google drive link above
1)the picture on screen is yellowish green
2)the bottom line displaying message in hindi language is red but is black
3) there are lines on picture due to vertical ic problem
4) 5 blinks led but tv works no shutdown just keeps on 5 blinks of small interval
5) no static to attract hair.
thanks
Jestine Yong
October 14, 2016 at 2:47 pm
Hi Hari,
Saw the photo-it seems this TV have many problems. You have to find out from the TV manual what does 5 blinks means. If it is referring to the vertical section then concentrate on this vertical circuit first. Just make sure the dc supply line to the vertical ic is good and no dry joints or even decayed glue in the circuit.
Jestine
Hari P
October 14, 2016 at 9:28 pm
hi,
found this from techlore
Five blinks - AKB circuit (automatic kine bias), the timer/standby indicator blinks for about 30 seconds then goes to the self-diagnosis function. Something is wrong with the video. Check video out, Q705, 732, 761 and other components on the C board , also check Q218, 219, 220 on the A board. In addition, unit could be in IK blanking, try turning up screen slightly.
but my screen is not blanking
Jestine Yong
October 20, 2016 at 9:07 pm
Hi Hari,
Sorry I do not have a direct solution for this.
Jestine
judith
January 22, 2017 at 10:59 pm
what the effect of resistance value of positor on picture color of crt lg tv
Jestine Yong
January 24, 2017 at 4:14 pm
Hi judith,
Do you mean you want to know the resistance of a posistor?
Jestine
Peter
March 11, 2017 at 10:50 am
How do u test a chopper transformer with a multimeter?
Jestine Yong
March 13, 2017 at 11:27 am
Hi Peter,
You need a ring tester such as the one in the below link to test the primary winding:
http://www.electronicrepairguide.com/blueringtesterresult.html
Normal multimeter with resistance checking can't test it if there is a shorted winding.
Jestine
ajay
May 18, 2017 at 12:07 pm
Hi sir jestine,
Posistor has no specific value right? We can substitute it from other junkboard as long as it is ok, it will work fine? and as long as it has three legs in it. Right?
Jestine Yong
May 18, 2017 at 8:43 pm
Hi Ajay,
It has part number and you can use junk posistor to test it out.
Jestine
Dinakaran
June 14, 2017 at 2:26 am
my crt tv on ,suddenly off how to fix it sir
Jestine Yong
June 14, 2017 at 11:40 am
Hi Dinakaran,
May i know what have you checked?
Jestine
Dinakaran
June 14, 2017 at 2:45 pm
sir how to check flyback transformer in multimeter
Jestine Yong
June 15, 2017 at 11:27 am
Hi Dinakaran,
You need a blue ring tester to check the flyback especially the primary winding.
http://www.electronicrepairguide.com/blueringtesterresult.html
Jestine
Dinakaran
June 16, 2017 at 5:00 pm
sir how to check resistor fault in tv
Jestine Yong
June 20, 2017 at 11:04 am
Hi Dinakaran,
I suggest that you get Humphrey's ebook as he covers the way how to check faults in TV:
http://www.electronicrepairguide.com/crt-tv-repair-ebook.html
Jestine
Ravi Bhosale
August 12, 2017 at 2:33 pm
What is the price of EPCOS ptc for CRT color TV???
Jestine Yong
August 14, 2017 at 10:38 am
Hi Ravi,
Sorry I do not sell parts and do not know about the price.
Jestine
Larry
August 14, 2017 at 10:53 pm
Hi. I have CRT TV which has shorts and blows fuses. Main filter was open and I replaced. Upon testing, degaussing coil shorts the fuse. When I remove degaussing coil connector tv powers on well. When I test using digital multimeter coil, it is shorted. When is test PTC it has a values of 22ohms and coil has 8ohms. Is it supposed for coil to short? Advice please
Jestine Yong
August 16, 2017 at 9:31 pm
Hi Larry,
Yes the coil can short and it can only be measured by using the ring tester. DMM only reads resistance. A shorted coil also have resistance thus it is not accurate to measure it using DMM.
Jestine
Michael
September 2, 2017 at 9:33 pm
Wonderful stuff Jestine...keep it up
Shah
November 6, 2017 at 10:38 am
Hi jestine..
My panasonic sophia 29inch tv fuse blown even changed new...then i saw 2 posistor was cracked on top.i cant get the same posistor so i just changed with what the shop guy have.The tv worked for a week..then when watching tv for long time the fuse blown again...is it becoz i use different posistors...thanks
Jestine Yong
November 7, 2017 at 1:09 pm
Hi Shah,
Possible but it can also be caused by shorted components such as bridge rectifier, power fet, power ic and etc.
Jestine
Shah
November 7, 2017 at 3:58 pm
Thanks jestine...i will try to check the bridge rectifier 1st...
Shah
November 8, 2017 at 8:44 am
Hi jestine
I checked the rectifier..the positif leg shows reading of 0.897 while other legs within 0.5 range...is it ok?thanks
Jestine Yong
November 9, 2017 at 10:30 am
Hi Shah,
I suggest that you follow the video on how to test the rectifier:
https://www.youtube.com/watch?v=dqkT6hF0O3E
Jestine
saidi
June 24, 2018 at 3:50 am
You realy boostup me to invest my time in dealing with electronics Justice. You're so great!
suryo w
December 21, 2017 at 7:14 pm
Hello sir
I have 3 pin ptc that keeps blowing up, pin 1 & 2 connect to both the ac input line and pin 3 connect to degaussing yoke. The one that keep blow up are resistor between pin 1 & 2(the one that connect to both ac line) do you have any suggestions what can cause the problem (it's old 20 inch Panasonic t2088an crt TV, I have giving up looking for the schematic diagram online)
Thanks in advance
Jetsdi
May 20, 2018 at 8:16 am
Sir jestine what is the main cause, i mean in all cases of blown fuse, what is the majority that cause the fuse to blow? Thank you
Jestine Yong
May 22, 2018 at 9:34 am
Hi Jetsdi,
Mainly are due to shorted bridge rectifier.
Jestine
Jetsdi
May 24, 2018 at 4:06 am
Thanks you sir
Les
June 12, 2018 at 11:07 am
Good day Sir, is it normal for a posistor to produce heat that much? i did not connect my de gaussing coil while voltage testing and after turning on the unit again, it became on standby mode. i touched the posistor and it produces too much heat. Thank you and more power.
Jestine Yong
June 13, 2018 at 9:21 am
Hi Les,
Yes it can get quite hot.
Jestine
lenny
June 17, 2018 at 11:52 pm
My crt ttv fuse blow n posistor got completely burn ... gaussing tested using DMM n its reading s 234ohm s..what could be possible problem. .
Sai bharath Devalla
August 15, 2018 at 9:21 pm
Hello
I'm using LG CRT TV since 6 years. It works fine up to last year.
But now it was not switching on when the temperature is low.
When temperature is sufficient it was switching on.
Which component will cause the problem
Okon
March 18, 2019 at 6:20 am
sir. My 21" LG CRT TV was making a sparking sound that won't last up to a second. each time, it will affects either the picture or sound. at a point, it went completely blackout.
it will show standby light, but the set will go off completely while trying to start..
I changed the flyback transistor that was short.
Now the TV will attempt a starting sound but go off immediately the glow sound starts...
what could be the problem sir?
andres
November 20, 2019 at 10:07 pm
hello, what about a ptc who constantly burn even if is change for one new?
Mark Alan Kirby
January 19, 2020 at 10:35 am
Hello. I have a PTH451C posistor in what looks to be a Orion CRT in a arcade game. I have no picture and this posistor gets hot after a couple minutes. Is this part defective? Thanks
Jestine Yong
January 20, 2020 at 10:28 am
Hi Mark,
It is normal for posistor to get hot but it cannot go too hot where your finger can't touch it.
Jestine
Emmanuel Haruna
August 16, 2020 at 8:55 pm
Hello Justine sir,
Pls I have a 21 Lg TV that the posistor material inside is completely shatter, fuse burn all due to a high voltage ,the STR reading is OK,though am still yet to replace the posistor sir, does it mean once I replace the posistor the system automatically come up? Thank you.
Jestine Yong
August 18, 2020 at 11:37 am
Hi Emmanuel,
You need to check the components that is corresponding to the posistor. If all checked to be good then only you place in the posistor and power it on.
Jestine
Debashish Saha
August 24, 2020 at 7:22 pm
I need a Thermistor for Samsung 17" 753 SyncMaster Monitor.
The part number is CMS44090Q
Jestine Yong
August 25, 2020 at 10:54 am
Hi Debashish,
Sorry we do not sell parts
Jestine