hi folks –

Please see pic below.



Can anybody tell me if this fuse is meant to be removable? It seems like it’s just pressed between the 2 caps on the ends which in turn are soldered on the board. Looks to me like it’s supposed to come out without unsoldering, but if so I don’t know how to go about it. Afraid I might ruin the fuse holder.

The circuit board accompanies the ballast for my UV filter. I am doing re-piping work and without thinking I plugged in the ballast without the UV bulb in the socket. Heard something like a pop and the led on board now doesn’t light. I checked across the fuse with an ohmmeter and it seems like the fuse is blown. But I can’t see anything at all in the fuse, like a burnt wire or something? Looks empty? Even with a magnifying glass (I have bad eyes.)

Any help would be greatly appreciated!

 

That fuse is soldered to the board.

 

You can't test the fuse with it connected to the cb, and as Luana said, it is soldered in. If it were me, with fat fingers and bad eyesight to boot, too, I would take it to a TV repairman/woman and see if they could replace it for you. You or I do it, and we'd melt something.

 

Shucks! Gotcha guys, thanks. Now that I think about, yea, I sure see why you can’t test the fuse with it connected to the cb. Mental lapse. Off to find someone who can do it.

You stopped me from going off on a tangent. Big help. Thanks!

 

Sure you can test it in place...a good fuse will read 0 (or real darn close to it!) on your lowest scale, you may need to swap the leads end for end to be sure. Almost any other electronic component will give you several ohms or hundreds of ohms if you do the swap of leads.

If you read 0 both ways...99.9% the fuse is good. Anything else (say...above 5), it's blown and you are reading the circuit resistance.

I actually just checked some auto fuses right out of the box and they read slightly LOWER than just shorting the leads. 1.1 ohm vs 1.3.

 

Hey thanks Vic! (I’m a Vic too, not many of us around.)

I had my digital meter scale set to 100 ohms. It sits there blinking 100 ohms with the leads just hanging in air. With the leads shorted I get 00.1 ohms. Putting the leads across some little tiny fuses I had sitting around I also get about 00.1 ohms.

With the leads put across the fuse on board I get no reading, i.e. the meter just continues to blink 100 ohms. If I reverse the probes across the fuse I get the same thing, no reading the meter just continues to blink 100 ohms.

Seems like that would mean the fuse must be bad?

 

It's blown....

You could prob find solder-in fuses at an electronics supply...but doubt if anything like Radio Shack would have them. If you know how to solder and want to get creative...buy an inline fuse holder and solder it in, carefully routing the leads outside of the case.

Make sure it's rated for the correct voltage/current.

 

Thanks Vic. Good information and good idea.

I think this is the time for me to get a little creative. Can’t see what I could lose.

 

There is a way to replace the fuse that is a bit crude but may be doable by a first timer if you have some electronic soldering experience. I would use a soldering gun quickly but a low wattage soldering pen is safer.

Clip the wires as close to the fuse caps as you can.
Tin the end caps of the new fuse. Use only rosin core solider.
Check that the new fuse is still good.... should be but a check now is good insurance.
Wrap the lower half of each of the two leads left on the board with about a quarter sheet of toilet paper almost dripping with distilled water.
Tin the top quarter of the two leads.

Now you probably need the hands of a friend. With tweezers or needle nose pliers have your friend hold the fuse in place and lead against it while you solder it. First melt the tinning and see if you can flow it together. Add a little solder if needed. Very important you use only rosin core solder.

Remove the toilet paper and be sure the board is dry before testing.

 

If the fuse is connected to other circuitry, your meter will read around that circuitry and not through the fuse if it is still connected. One end should be disconnected for testing.

 

Larry...buddy...a good fuse is a short bypassing all the circuits...a bad fuse will read through the circuits. Even a forward biased diode will read higher than a good fuse. Thats why I said check both ways just to be sure you aren't reading the circuit resistance.

Any other component has to be disconnected to get a good reading...but not a fuse. Unless there has been a short on both side of the fuse to the same electrical point.

 

Thanks ray, very good detailed instructions. What do I have to lose by trying it. Nothing as far as I’m concerned.

I know nothing but that’s what I thought.

Thanks guys for your help.

 

Vic, I wasn't treating this fuse as a "master" fuse, as some circuits loop and have additional fuses. I have, in earlier years, checked resistance of a known blown fuse connected to the cb, and the circuit ahead of the fuse just looped around giving me resistance, so I never trusted that method of checking fuses. I think a voltage check is more indicative of a blown fuse than a resistance check.

 

True dat! Voltage is a better indicator...

 

hi guys –

One more (OK two more) question please. I’m doing fuses 101. Is that fuse in the picture what is known as a “pigtailed” fuse? So the way they do it is: it's a complete package and the pigtails are just soldered onto the board?

Also I think I can read 7.5 amps on that fuse. I know you don’t have any information but would 7.5 amps be plausible?

 

Correct...thats the name. Use Google and you'll see many examples.

Seems a bit high...but very likely thats correct. You should be able to read it pretty clearly once its out. I can see the 250V very clearly.

 

Gotcha Vic. thanks again!

 

Yes, but urn-soldering then re-soldering to the board is more likely to cause damage then the method I suggested. As I said a pro would judge it crude because you are reusing the original leads. Just use a fuse without leads for my method. Safer staying away from the board IMHO.

 

Oh yeh! I figured your method would be safer. That will be my route.

thanks ray!