De-Gauss coil thermistors in TVs
 

Those usually 3-legged black blocks containing 2 PTC disc thermistors.
One of a few tens of ohms (cold) feeding to the coil and one of a few
hundred ohms (cold) connected between live and neutral , what is the
function of the one across the mains ?
As that one is separated from the other by 2 sets of spring clips, it cannot
be there for indirectly heating the one feeding the coil for quick
completion.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

De-Gauss coil thermistors in TVs
 

"N Cook" wrote in message
...
Those usually 3-legged black blocks containing 2 PTC disc thermistors.
One of a few tens of ohms (cold) feeding to the coil and one of a few
hundred ohms (cold) connected between live and neutral , what is the
function of the one across the mains ?
As that one is separated from the other by 2 sets of spring clips, it
cannot
be there for indirectly heating the one feeding the coil for quick
completion.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


Isn't the second one across the back side of the first, rather than directly
across the mains? Sort of a two thermistor series / shunt arrangement. I
seemed to recall from my long-ago theory days, that they were the inverse of
each other, and that the one that's across is initially high resistance, and
gets lower as it heats up, to shunt the degausing coils, mitigating their
effect, and keeping the series thermistor hot - and hence in the high
resistance condition - by continuing to draw just enough current through it
to do that. Could be wrong - it's been a long time ago - but it 'feels'
right, and seems to work, in my head at least ... !!

Mind you, I'm going back to when they were two (definitely) different
individual components. The series one was a granular grey, and the shunt was
a little smaller diameter and a little thicker, with a mainly blue (painted)
body, with a yellow stripe at the top. I've probably still got some
somewhere. But perhaps they've come up with some other way of doing it since
they've encapsulated the two elements together.

Arfa

De-Gauss coil thermistors in TVs
 

Arfa Daily wrote in message
...

"N Cook" wrote in message
...
Those usually 3-legged black blocks containing 2 PTC disc thermistors.
One of a few tens of ohms (cold) feeding to the coil and one of a few
hundred ohms (cold) connected between live and neutral , what is the
function of the one across the mains ?
As that one is separated from the other by 2 sets of spring clips, it
cannot
be there for indirectly heating the one feeding the coil for quick
completion.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


Isn't the second one across the back side of the first, rather than
directly
across the mains? Sort of a two thermistor series / shunt arrangement. I
seemed to recall from my long-ago theory days, that they were the inverse
of
each other, and that the one that's across is initially high resistance,
and
gets lower as it heats up, to shunt the degausing coils, mitigating their
effect, and keeping the series thermistor hot - and hence in the high
resistance condition - by continuing to draw just enough current through
it
to do that. Could be wrong - it's been a long time ago - but it 'feels'
right, and seems to work, in my head at least ... !!

Mind you, I'm going back to when they were two (definitely) different
individual components. The series one was a granular grey, and the shunt
was
a little smaller diameter and a little thicker, with a mainly blue
(painted)
body, with a yellow stripe at the top. I've probably still got some
somewhere. But perhaps they've come up with some other way of doing it
since
they've encapsulated the two elements together.

Arfa



This is the basic circuit from the schematic and values from an actual TV.
The 16 ohm one is PTC but the 470 one across the mains is NTC heating each
in turn with a soldering iron. The schematic states PTC for both so more
mystery
On closer inspection the two discs are in good thermal contact to the
central pin extended to a dividing metal disc but good thermal contact, the
spring plate connections are on the outer contacts.

ASCII , view in Courier or perhaps Properties/ Message Source

|-------------
\.-. |
|\| C|
16 | |\ C| degauss coil
'-' C|
| |
L ------------| |
\.-. |
|\| |
240V 470| |\ |
'-' |
| |
N -------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

De-Gauss coil thermistors in TVs
 

"N Cook" writes:

Arfa Daily wrote in message
...

"N Cook" wrote in message
...
Those usually 3-legged black blocks containing 2 PTC disc thermistors.
One of a few tens of ohms (cold) feeding to the coil and one of a few
hundred ohms (cold) connected between live and neutral , what is the
function of the one across the mains ?
As that one is separated from the other by 2 sets of spring clips, it
cannot
be there for indirectly heating the one feeding the coil for quick
completion.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


Isn't the second one across the back side of the first, rather than
directly
across the mains? Sort of a two thermistor series / shunt arrangement. I
seemed to recall from my long-ago theory days, that they were the inverse
of
each other, and that the one that's across is initially high resistance,
and
gets lower as it heats up, to shunt the degausing coils, mitigating their
effect, and keeping the series thermistor hot - and hence in the high
resistance condition - by continuing to draw just enough current through
it
to do that. Could be wrong - it's been a long time ago - but it 'feels'
right, and seems to work, in my head at least ... !!

Mind you, I'm going back to when they were two (definitely) different
individual components. The series one was a granular grey, and the shunt
was
a little smaller diameter and a little thicker, with a mainly blue
(painted)
body, with a yellow stripe at the top. I've probably still got some
somewhere. But perhaps they've come up with some other way of doing it
since
they've encapsulated the two elements together.

Arfa



This is the basic circuit from the schematic and values from an actual TV.
The 16 ohm one is PTC but the 470 one across the mains is NTC heating each
in turn with a soldering iron. The schematic states PTC for both so more
mystery
On closer inspection the two discs are in good thermal contact to the
central pin extended to a dividing metal disc but good thermal contact, the
spring plate connections are on the outer contacts.

ASCII , view in Courier or perhaps Properties/ Message Source

|-------------
\.-. |
|\| C|
16 | |\ C| degauss coil
'-' C|
| |
L ------------| |
\.-. |
|\| |
240V 470| |\ |
'-' |
| |
N -------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Geez, there's a program to draw mediocre ASCII schematics? :)

I believe your discarded explanation is correct. The second one
is there to keep the series thermistor hot after the initial surge
through the degauss coil.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

De-Gauss coil thermistors in TVs
 

"N Cook" wrote in message
...
Arfa Daily wrote in message
...

"N Cook" wrote in message
...
Those usually 3-legged black blocks containing 2 PTC disc thermistors.
One of a few tens of ohms (cold) feeding to the coil and one of a few
hundred ohms (cold) connected between live and neutral , what is the
function of the one across the mains ?
As that one is separated from the other by 2 sets of spring clips, it
cannot
be there for indirectly heating the one feeding the coil for quick
completion.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


Isn't the second one across the back side of the first, rather than
directly
across the mains? Sort of a two thermistor series / shunt arrangement. I
seemed to recall from my long-ago theory days, that they were the inverse
of
each other, and that the one that's across is initially high resistance,
and
gets lower as it heats up, to shunt the degausing coils, mitigating their
effect, and keeping the series thermistor hot - and hence in the high
resistance condition - by continuing to draw just enough current through
it
to do that. Could be wrong - it's been a long time ago - but it 'feels'
right, and seems to work, in my head at least ... !!

Mind you, I'm going back to when they were two (definitely) different
individual components. The series one was a granular grey, and the shunt
was
a little smaller diameter and a little thicker, with a mainly blue
(painted)
body, with a yellow stripe at the top. I've probably still got some
somewhere. But perhaps they've come up with some other way of doing it
since
they've encapsulated the two elements together.

Arfa



This is the basic circuit from the schematic and values from an actual TV.
The 16 ohm one is PTC but the 470 one across the mains is NTC heating each
in turn with a soldering iron. The schematic states PTC for both so more
mystery
On closer inspection the two discs are in good thermal contact to the
central pin extended to a dividing metal disc but good thermal contact,
the
spring plate connections are on the outer contacts.

ASCII , view in Courier or perhaps Properties/ Message Source

|-------------
\.-. |
|\| C|
16 | |\ C| degauss coil
'-' C|
| |
L ------------| |
\.-. |
|\| |
240V 470| |\ |
'-' |
| |
N -------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)



Based on that then, you'd have to say that it was just a physical contact
thing. I'll have to see if I've still got any of my old TV schematics about,
to see what the configuration was before they put both together in a single
package.

Arfa

De-Gauss coil thermistors in TVs
 

Sam Goldwasser wrote in message
...
"N Cook" writes:

Arfa Daily wrote in message
...

"N Cook" wrote in message
...
Those usually 3-legged black blocks containing 2 PTC disc
thermistors.
One of a few tens of ohms (cold) feeding to the coil and one of a
few
hundred ohms (cold) connected between live and neutral , what is the
function of the one across the mains ?
As that one is separated from the other by 2 sets of spring clips,
it
cannot
be there for indirectly heating the one feeding the coil for quick
completion.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


Isn't the second one across the back side of the first, rather than
directly
across the mains? Sort of a two thermistor series / shunt arrangement.
I
seemed to recall from my long-ago theory days, that they were the
inverse
of
each other, and that the one that's across is initially high
resistance,
and
gets lower as it heats up, to shunt the degausing coils, mitigating
their
effect, and keeping the series thermistor hot - and hence in the high
resistance condition - by continuing to draw just enough current
through
it
to do that. Could be wrong - it's been a long time ago - but it
'feels'
right, and seems to work, in my head at least ... !!

Mind you, I'm going back to when they were two (definitely) different
individual components. The series one was a granular grey, and the
shunt
was
a little smaller diameter and a little thicker, with a mainly blue
(painted)
body, with a yellow stripe at the top. I've probably still got some
somewhere. But perhaps they've come up with some other way of doing it
since
they've encapsulated the two elements together.

Arfa



This is the basic circuit from the schematic and values from an actual
TV.
The 16 ohm one is PTC but the 470 one across the mains is NTC heating
each
in turn with a soldering iron. The schematic states PTC for both so more
mystery
On closer inspection the two discs are in good thermal contact to the
central pin extended to a dividing metal disc but good thermal contact,
the
spring plate connections are on the outer contacts.

ASCII , view in Courier or perhaps Properties/ Message Source

|-------------
\.-. |
|\| C|
16 | |\ C| degauss coil
'-' C|
| |
L ------------| |
\.-. |
|\| |
240V 470| |\ |
'-' |
| |
N -------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Geez, there's a program to draw mediocre ASCII schematics? :)

I believe your discarded explanation is correct. The second one
is there to keep the series thermistor hot after the initial surge
through the degauss coil.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above
is
ignored unless my full name AND either lasers or electronics is included
in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

I found a similar one and tested that and NTC again for the "heater"
section.
But that can't be the case, presumably it must initially be NTC and then go
positive above 150 degrees or something.
I will try heating longer and see what happens

I assumed the one feeding the coil would reach some stable elevated
resistance and stay in that stable state at some elevated temp until
switched off.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

De-Gauss coil thermistors in TVs
 

Yes the heater one dropped 50 ohms or so and then rattled rapidly up to more
than 150K with continued heating from a soldering iron.

So I've learnt something else today.

Now just to discover the source of manure smells off kit.
Currently orking on a Fender Pro 185 from 1989 and the workshop has a
noticeable smell of manure. On poking my nose directly over caps,
transformer, cabinet (for fish glue or something) etc I cannot localise it.
I looked at another of this exact same model a few months ago and no such
smell.
A year ago I repaired a JBL domestic amp from the 1960s and that had a very
strong , even stronger, manure smell, but again could not localise the
smell.
With reservations about breaking the "special relationship" one common
factor is they were both made in the USA.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

De-Gauss coil thermistors in TVs
 

On Mon, 03 Sep 2007 08:30:01 GMT, "Arfa Daily"
put finger to keyboard and composed:


"N Cook" wrote in message
...
Those usually 3-legged black blocks containing 2 PTC disc thermistors.
One of a few tens of ohms (cold) feeding to the coil and one of a few
hundred ohms (cold) connected between live and neutral , what is the
function of the one across the mains ?
As that one is separated from the other by 2 sets of spring clips, it
cannot
be there for indirectly heating the one feeding the coil for quick
completion.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


Isn't the second one across the back side of the first, rather than directly
across the mains? Sort of a two thermistor series / shunt arrangement. I
seemed to recall from my long-ago theory days, that they were the inverse of
each other, and that the one that's across is initially high resistance, and
gets lower as it heats up, to shunt the degausing coils, mitigating their
effect, and keeping the series thermistor hot - and hence in the high
resistance condition - by continuing to draw just enough current through it
to do that. Could be wrong - it's been a long time ago - but it 'feels'
right, and seems to work, in my head at least ... !!

I think that's correct. Whenever I suspected a 3-pin thermistor as the
cause of a blown fuse, I used to shake it and listen for rattling.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.