Does anyone know what this component is in a circuit board?

Hi, this is not necessarily related to automation, but it is related to electronics and I like to mess around with my electronics when they go bad. This is my lcd screen power supply; which stopped working...



I was wondering if anyone knew what this component is? First I thought it was a diode, but it looks more like a fuse. It has no resistance or conductivity. A diode test does not give expected results.

What do y'all think???

diode.
You can even glimpe the symbol below that indicates a diode.

edit: It could also be a zener diode. Take a closer look at the symbol underneath that will reveal it exactly.

Hi, thanks for the reply!

I removed the "diode" and it looks like this -N- with a circle around it???

PS: In fact, it looks exactly as the symbol to the right, the one labeled "SG702"

I'm googling for a electrical symbol chart to see what it is...

Looks like a diode, but the symbol is for a varistor

http://preher-tv.blogspot.com/2010/07/varistors.html

Makes sense that the prefix is "SG" as in SurGe suppressor

I've never seen a varistor that looks like that, but a quick search found this:

http://www.amazon.com/NTE600-Silicon-Varistor-Temperature-Compensating/dp/B007Z7QBXQ



-Eric

Eric Nelson said:

Looks like a diode, but the symbol is for a varistor

http://preher-tv.blogspot.com/2010/07/varistors.html

Makes sense that the prefix is "SG" as in SurGe suppressor

I've never seen a varistor that looks like that, but a quick search found this:

http://www.amazon.com/NTE600-Silicon-Varistor-Temperature-Compensating/dp/B007Z7QBXQ



-Eric

Click to expand...

Interesting... I tried looking for the symbol and did not find it anywhere!

Btw, do you know what it means when it has the circle and when it doesn't?

You can see a symbol without the circle a little bit to the right with label "VZ704"... That label does look like it indicates a varistor???

Thanks!

SergioB said:

Hi, this is not necessarily related to automation, but it is related to electronics and I like to mess around with my electronics when they go bad. This is my lcd screen power supply; which stopped working...

I was wondering if anyone knew what this component is? First I thought it was a diode, but it looks more like a fuse. It has no resistance or conductivity. A diode test does not give expected results.

What do y'all think???

Click to expand...

Diodes would look like this:
Image 1 diode
Image 2 Zener diode

I don't know for sure. If it is a Zener diode, then they badly butchered the standard Zener symbol.

The other symbol labels seem to begin with a label that indicates the function (F = fuse, J = Jumper, C = Capacitor, L = inductor). Using that as a hint, what could "SG" mean? Switch-something-or-other?

The "Z" is a very old symbol for an overload contact. I remember drawing hundreds of those Z symbols for motor overloads on motor starters.

Could it be some type of overload switch, similar to a circuit breaker? Checks: no resistance, yes the resistance should be almost 0 if it is still good, but infinity or open if it has tripped. No conductivity: yes, if it has opened on overload. Plus it doesn't look like a diode, but "more like a fuse". The only thing I can't figure is what the G stands for in "SG701".

Maybe it is a varistor, although I am used to seeing a different symbol for the varistor, a cylinder with the Z drawn across it. It does not look like a varistor either.

You can see a symbol without the circle a little bit to the right with label "VZ704"... That label does look like it indicates a varistor???

Click to expand...

The round tan VZ702 and VZ70 look more like the usual varistors.

If it is a type of varistor, then why is there only 1 of this type (in the view that we have)? Is there another "SG" component anywhere on this circuit board? What are the small "Z"'s (Z701, Z702) next to Fuse F701?

The mystery continues, hehe... Here's a close up of the removed component (does it look like the ends melted inside???):

Looking at the picture, I am betting on a type of time-delayed thermal overload switch (or fuse).

Hmmm...I wonder if the ends are made to turn red when it trips? SG: SiGnal Overload Switch?

Can you see if there is a break in the spiral wire around the black cylinder-insulator? It looks as if the right end has burned away.

Lancie1 said:

Looking at the picture, I am betting on a type of time-delayed thermal overload switch (or fuse).
Can you see if there is a break in the spiral wire around the black cylinder-insulator? It looks as if the right end has burned away.

Click to expand...

It does doesn't it? I can't really tell if it's burned away, in fact the close up pic shows the best detail I can see.

Thanks everyone!!!

Try to measure the resistance - both ways.

Looking closer, that inner black cylinder looks almost like a Bussman miniature time-delay Slow Blow ceramic-type MDA or MDL fuse.

JesperMP said:

Try to measure the resistance - both ways.

Click to expand...

Resitance is OL both ways.

Using a Fluke? If so, OL means OverLoad or unmeasurable infinite resistance, same as an open circuit.