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Please Help Identify this Component :)

zebetz

New Member
Hi all,

I am trying to repair this piece of equipment (it's an LED light) and the only obvious thing wrong with it is this component. I took these photos - The board shows 250v and what looks like a resistor symbol inside an oblong circle. The component is broken and hard to read but shows N and 5D- something... Any help would be so greatly appreciated! Many thanks.

Kind regards,

Will
 

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ramondo

Member
I believe it is a varistor, ( an item to limit inrush current.) Look for ptc,ntc,surge type items on google. I last saw these when using degaussing coils on tube tv's.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Yes, it's simply a surge limiter, it's clearly labelled TH1 (for thermistor) - it's a negative temperature coefficient thermistor, and as ramondo mentioned, it's commonly called a varistor in these applications.

You could replace it with a 4.7 or 10 ohm 7W resistor if you can't easily locate a varistor - although I believe most major suppliers have them (in loads of different values).
 

sagor1

Active Member
If the varistor blew, it may have protected everything else, but maybe not. Check the first few devices after the thermistor, like fuses, diodes, etc.
Something caused it to blow. It could have been overvoltage on input, or some device failure past the thermistor, causing a current surge.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
If the varistor blew, it may have protected everything else, but maybe not. Check the first few devices after the thermistor, like fuses, diodes, etc.
Something caused it to blow. It could have been overvoltage on input, or some device failure past the thermistor, causing a current surge.

It 'could' be caused by the PSU having blown, but those varistors commonly die on their own, they aren't very reliable devices.

Some manufacturers use varistors, some use resistors, and the resistors are far more reliable - if the resistor dies, then it's pretty well guaranteed that the PSU has blown.

But it's certainly worth checking the switching device, and the mains rectifiers.
 

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