Author Topic: 12V TV Fuse identification  (Read 1251 times)

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Online splin

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12V TV Fuse identification
« on: May 22, 2016, 06:17:03 pm »
My neighbour connected 12V with the wrong polarity to his Kenmax 19LVD00D1 19" LCD TV and consequently I've been asked to take a look. A 3A 250V fuse has blown so hopefully it will be easy to fix.

The fuse is a through hole glass type, 11mm x 4mm covered with black heat shrink marked "BESR TUBE". The fuse itself is marked '3A 250V' at one end and '3D' plus some certification symbols. One I can't identify is an '<' in a circle, but rotated anticlockwise such that the lower line in the < symbol is horizontal.

The fuse wire is straight so I assume it is simply a medium speed type but the marking on the PCB is T3A/250V so does that mean a slow blow? Any recommendations as to what type I should replace it with?
 

Online tautech

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Re: 12V TV Fuse identification
« Reply #1 on: May 22, 2016, 09:30:03 pm »
If you have a graveyard of old PC PSU's some of them might have TH mains fuses you can re-purpose.  ;)

Surely you can but these things but I'm not sure where.  :-//

Otherwise try to find some that have the fuse element soldered in and add the wire extension needed to make TH use possible.
You might have to play around with different temp solders to prevent the wire extensions falling of when soldering to the PSU pads. Otherwise use some "clip on" heatsinking to keep the heat from getting to the fuse.
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Online splin

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Re: 12V TV Fuse identification
« Reply #2 on: May 23, 2016, 02:20:48 am »
If you have a graveyard of old PC PSU's some of them might have TH mains fuses you can re-purpose.  ;)

Surely you can but these things but I'm not sure where.  :-//

Otherwise try to find some that have the fuse element soldered in and add the wire extension needed to make TH use possible.
You might have to play around with different temp solders to prevent the wire extensions falling of when soldering to the PSU pads. Otherwise use some "clip on" heatsinking to keep the heat from getting to the fuse.

Thanks tautech. I had considered doing exactly that but through hole fuses do seem to be available on ebay.

My main question though was what *type* of fuse should I use - a standard speed or slow, 'T' type? Since it won't be easy to replace I don't want to use a standard fuse if it needs a slow blow because of inrush currents. On the other hand I don't want to use a slow fuse if it isn't required, reducing its protection.
 

Online tautech

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Re: 12V TV Fuse identification
« Reply #3 on: May 23, 2016, 02:31:59 am »
IMO slow, in order to withstand power on inrush currents of a SMPS.

But as you don't know the design tolerances there's no way to know if the designer didn't allow for inrush.
Often if slow is required it's marked on the overlay.
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Offline TheMG

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Re: 12V TV Fuse identification
« Reply #4 on: May 23, 2016, 04:23:48 am »
Before you go out of your way to find an exact replacement fuse, I would just throw in whatever 3A fuse you can find just so you can at least test the TV and assess whether there is anything else wrong with it.

If the manufacturer did not include a reverse polarity protection diode in the design, there is almost guaranteed to be some damage to the power supply circuitry. Even if it is equipped with a reverse diode, a lot of times that will fail short by the time the fuse opens.

So there definitely are some other things to check.
 


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