Glass PCB fuse

[pcolbeck]

I need to replace a glass fuse on a PCB (its on the PCB for the sensor on PVR external light). Its 250V 3 amp and looks like this:



anyone know where I can get these in the UK. I cant find them at Maplin or RS, well they do similar but without the tails.

[rafletcher]

The tails are I suspect soldered on anyway.

[Valiant]

Yip the bulb is available anywhere including Maplins, RS, CPC et all and I've had them before. The tails are just soldered on, so you can either snip and replace or use some wire and redo.

[redshift]

Or solder a 20mm PCB fuse holder into place, then you don't need to re-solder next time the fuse blows.

[pcolbeck]

Or solder a 20mm PCB fuse holder into place, then you don't need to re-solder next time the fuse blows.

Thats a good idea !

I might get a solder station as well as my old soldering iron is rubbish. It took me ages to desolder this fuse.

[Valiant]

The Tenma ones from CPC are surprisingly good I find.

[Biggsy]

You can get glass fuses with leads already attached, but the ones I've seen (CPC and eBay) have the leads in-line ("axial") with the fuses, rather than at 90 degrees.  You could simply bend them, though, depending on what you're going to fit them in/on.

With or without leads, you'll need to chose between quick and slow blow.  A code on the fuse may give a clue.

CPC used to do free post with any order, but they now say £10 minimum order for card transactions.  Bump up your order with your soldering iron/station and leaded solder!

For low cost but decent solder stations, I recommend Aoyue.  But a non-station Antex or Maplin iron is good enough for basic jobs.  Make sure any iron has replaceable tips, and don't just have a pointy conical tip.  Don't bother with lead-free solder.  Sorry if I'm sucking your granny's eggs.

[pcolbeck]

My current iron is an Antex 25w but I only have a very narrow conical tip. Thats the problem I think as it makes it hard to get good heat  transfer.

[Feanor]

Put a wee blob of fresh solder onto the tip first.

This wee blob will then 'wet' the joint you are trying to un-solder and carry the heat.

[pcolbeck]

Put a wee blob of fresh solder onto the tip first.

This wee blob will then 'wet' the joint you are trying to un-solder and carry the heat.

That's how I de-soldered it. That and a nice solder sucker to slurp it up once it was liquid.

[aidan.f]

last week cpc had free p&p on all orders.

[Diver300]

You could use just about any 3A wire ended fuse, as long as it is rated to 250 V or more.

http://uk.farnell.com/multicomp/mcpmp-3a-250v/fuse-axial-slow-blow-3a/dp/1566020

and there are probably places where you don't have to buy 10 and pay for postage.

[Vince]

Any idea why the fuse blew?

[pcolbeck]

None. The light just stopped working. Its an outside light mounted on a wall so its possible water got in or something. The PCB looks fine with no obviously blown capacitors. Its £70 for a new light so worth having a go at putting a new fuse in and seeing if works again.

[Feanor]

Fuses do fail for no real reason.

If the inside of the glass is black with vaporised fuse wire, then Something Bad happened.
But if the fuse looks OK and simply has the wire dangling Open Circuit, then I'd try just replacing it.

<Naughty Advice: Sometimes, when a fuse is blowing and you can't determine WTF is doing the over-current, then shorting out the fuse will cause the fault to present at it's actual location, with a puff of magic smoke. /Naughty Advice>

[Kim]

My current iron is an Antex 25w but I only have a very narrow conical tip. Thats the problem I think as it makes it hard to get good heat  transfer.

Yes, conical tips are a work of Stan, and best kept for tactical melting of plastic.

What you really want for this sort of thing is a chisel tip - as you say, better heat transfer.

Also, 25W is a bit weedy - a *thermostatic* iron with a bit more power behind it will make all the difference for chunky things that dissipate heat, not to mention lead-free solder (which needs higher temperatures than the proper stuff).

[Kim]

<Naughty Advice: Sometimes, when a fuse is blowing and you can't determine WTF is doing the over-current, then shorting out the fuse will cause the fault to present at it's actual location, with a puff of magic smoke. /Naughty Advice>

Slightly less naughty advice:  An appropriately rated light bulb connected in place of the fuse makes a useful diagnostic for this sort of thing.  If it lights up, it'll show that something's still broken but hopefully limit current and prevent loss of magic smoke.  Better than popping loads of fuses while chasing down a fault, anyway.

[Biggsy]

I find an Antex 25W adequate when giving it plenty of time to heat up, but I don't use conical tips and do use leaded solder.  The Aoyue station I have as well is superior, but I sometimes prefer the portability of the simple Antex.

[pcolbeck]

Far ell don't do the Aoyou anymore but I have found someone else that does. What tips would the panel recommend to order with it ?

[Kim]

Of the multitude of tips that came with my Aoyue, I mostly use the 1.5mm chisel tip that didn't.  I've also got a 2mm chisel, which might be a better general-purpose electronics tip if you're not doing much SMD stuff^[1].

Other than that, there's an enormous bevel one that I've used a couple of times for really chunky wire (again, a chisel tip would be the best choice here, but there's not much in it), a ludicrousy fine conical tip that's good for precision plastic-melting, and a middle-of-the-range bevel tip that I've set aside for dealing with lead-free solder (they don't mix well).  And an assortment of conical and bevel tips in silly sizes that remain unused.


_{[1] SMD soldering is about using your jedi powers^[2] to manipulate surface tension, rather than a really small version of standard soldering, so tiny tips aren't as vital as you might assume.
[2] And flux, lots of flux.}

[Feanor]

For SMD, I'd advise a 'hoof' style tip, which holds a small reservoir of solder.
Dragging this along the legs of an SMD device ( with a bunch of practice! ) will leave exactly the correct amount of solder on each leg, nicely separated by capillary forces.

You can get away with a normal fine tip if you can sweep it across the legs carefully whilst feeding thin solder, but bridging is more likely.

As with all soldering, preparation is everything.
The board and pads need to be utterly clean under magnification.
The PCB will usually have 'wells' in it around the pads, to help prevent bridging.
A syringe with flux is essential.

If using traditional solder, a tiny dab on the tip to affix 2 diagonal corners.
Then the hoof tip to run across the legs.

If using a reflow hot-air gun, then a syringe of flux/solder mix applied *sparingly*, and be careful not to blow the device off position with the airflow.   The capillary forces will hold it in place, to an extent.

BTW, have you ever looked at solder paste under a microscope?
It's loads if tiny balls of solder ( like buckshot ) suspended in flux paste.
When you bring a reflow gun into play, the flux liquidises, and the little balls of solder roll about like balls in a kiddies ballpit.
It can be a right bugger to have them all 'join' into a designated bit of solder; you don't want stray balls left floating around. (!)

[Kim]

A syringe with flux is essential.

I quite like flux pens.  (Like a marker pen with flux in it rather than ink.)  Was it someone on here who mentioned them?

If using traditional solder, a tiny dab on the tip to affix 2 diagonal corners.
Then the hoof tip to run across the legs.

Or dragging outwards along the legs, repeating to remove solder if bridges are formed.  That's probably less fussy about tips (though I can't imagine a conical one is very good).  I should track down a hoof tip to fit my Aoyue, I don't think they make them themselves, but presumably someone else's tips fit.

BTW, have you ever looked at solder paste under a microscope?
It's loads if tiny balls of solder ( like buckshot ) suspended in flux paste.
When you bring a reflow gun into play, the flux liquidises, and the little balls of solder roll about like balls in a kiddies ballpit.
It can be a right bugger to have them all 'join' into a designated bit of solder; you don't want stray balls left floating around. (!)

I've yet to attempt anything with solder paste - just done it by hand with the iron - but the fiddliest I've attempted is TSSOP.  Doesn't sound much fun using paste with a rework gun (which, OTOH, is brilliant for de-soldering and dead handy for heatshrink).

[Biggsy]

The terms "chisel" and "bevel" get mixed up.  I think Aoyue, or Aoyue tip sellers, get them them the wrong way round (?).  www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=Aoyue+bevel+tip&_sop=15

I got a load of weird and wonderful Aoyue tips off eBay, but a medium what-most-Aoyue-tip-sellers-call bevel tip tends to live on my iron after all.  Also get a big fat one if you ever solder chunky cables.  You can also get extremely narrow and long ones that are almost conical, but with flats for better heat transfer, so you very rarely need an actual conical one.

[Kim]

Ah, marvellous(!)

Here's one of the best images of tips I could find:



It's the type on the left that I prefer (the ones ending in 'C' in Aoyue part numbers) - nice big contact area, and will tend to hold a blob of solder for the SMD stuff.  Aoyue seem to call this 'bevel', others seem to call it 'hoof'.  The seller I bought mine from called it 'chisel', but may well have been wrong.

The middle one is unambiguously conical.

The one on the right is symmetrical, with a similar face on the other side.  A good all-rounder, unless your iron has a fume extraction tube^[1] attached, in which case you're only going to ever use one side.  Is this the true 'chisel'?


_{[1] My station has one of these, and I reckon it's brilliant.  Some people find them annoying as they get in the way, and I probably wouldn't recommend them to complete newbies on that basis, but I only find it's a problem for fiddly repairs, and you can always detach the tube.}

[Biggsy]

I prefer the angle of the type on the right of the above picture for my Aoyue when sitting and resting my wrist on the table, but maybe that's a bad habit, and there isn't always clearance for the iron at that angle anyway.  It's not so available for the Antex mains iron (that I tend to use on my hands and knees).

^ETA:  I agree that the one on the left is the most sensible recommendation.  It's what irons used to come with (before the conical craze), and all that I used for the first couple of decades of my soldering.

The one on the right is symmetrical, with a similar face on the other side.  A good all-rounder, unless your iron has a fume extraction tube^[1] attached, in which case you're only going to ever use one side.  Is this the true 'chisel'?.

I think so.