Making a pig tail fuse - Page 1
Forum section: electronics / repair

author: rqsall
author_rank: Regular Contributor
timestamp: October 28, 2014, 11:46:07 am
content: Hello all,I'm trying to diagnose an old Goldstart oscilloscope. In doing so, the probe slipped and shorted the emitter and collector of the transistor in the CRT transformer oscillator, which blew the PCB mounted pig tail fuse that protects said circuit (it is fed unregulated straight from the power transformer and then rectified. The fuse is right after the rectifier save for a filter cap). It looks like this:http://uk.mouser.com/ProductDetail/Bussmann-Eaton/BK-GFA-3/?qs=sGAEpiMZZMsNIlwy3aAdUXrpTqS2Ux%2ftmL4bsj%2flpjk%3dand is rated at 125V/500mA. I have found some on ebay and other places, but they would take some time to arrive and they're also not cheap, especially counting shipping.I have fuses of the required rating, but they don't have leads on them. Is it a bad idea to solder some wires to a regular glass fuse?Thank you very much for any suggestions.

author: tom66
author_rank: Super Contributor
timestamp: October 28, 2014, 12:14:32 pm
content: I've tried it before with no success. The fuse caps couldn't be soldered to (in any reliable manner.)

author: wagon
author_rank: Frequent Contributor
timestamp: October 28, 2014, 12:17:13 pm
content: I've done it before. It's not ideal, but you can. Maybe you could wire in an 'inline' fuseholder too.

author: wagon
author_rank: Frequent Contributor
timestamp: October 28, 2014, 12:18:36 pm
content: I've found you often need to scrape away the plating on the fuse ends, to get the solder to stick. (lots of heat too)

author: Muttley Snickers
author_rank: Unknown
timestamp: October 28, 2014, 01:42:15 pm
content: As wagon mentioned,It can be a bit tricky but desperate times tend to call for desperate measures.I've had to do it a few times and this method has worked for me, I sand or file the ends of the caps to almost bare metal, then I clip on an aluminium alligator clip to the side of the cap, this is to draw heat away so as not to melt the glue between the glass and the cap. I use an antimony solder initially to tin the cap ends, then pre-tin the wires with 60/40 solder, then bobs your uncle. Multicore antimony solder is 95% tin and 5% antimony not generally recommend for electrical use, more suited to metal fabrication, but it will mix with 60/40 pretty well.Another more risky method is to get a metal sleeve close to the cap diameter, something like a BNC crimp ring, crimp the ring and the wire to the cap, but be delicate. then meter whilst wiggling the joint to ensure good contact,then heat shrink the ends leaving exposed glass for viewing.Disclaimer...........This is all a bit dodgy but it has in the past given me time to get hold of the original blown component.Others may have better solutions, all idea's are welcome as it can be a pain when this occurs.Muttley

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 28, 2014, 02:35:58 pm
content: http://www.ebay.com/itm/10Pcs-Littelfuse-Pico-Fuse-0-5A-0-5-Amp-1-2A-125V-/170578166583?pt=LH_DefaultDomain_0&hash=item27b7404337??

author: Muttley Snickers
author_rank: Unknown
timestamp: October 28, 2014, 02:57:53 pm
content: Alex,With all due courtesy and respect, he did indicate that he could get it off Ebay, the question was could he make one out of stuff he had at hand. It's also unlikey that he has antimony solder.My suggestion will probably be one of many that may become helpful to both him and others as well.Muttley

author: TonyStewart
author_rank: Contributor
timestamp: October 28, 2014, 03:01:52 pm
content: I have soldered in 30AwG magnet wire in a pinch.. And even worse., wrapped a 15A fuse in Alum foil.

author: Muttley Snickers
author_rank: Unknown
timestamp: October 28, 2014, 03:14:32 pm
content: I didn't want to mention the foil fuse, as people under the age of 18 could be reading this stuff.Those fixes are best left to the adult's.Muttley

author: rqsall
author_rank: Regular Contributor
timestamp: October 28, 2014, 03:16:39 pm
content: Quote from: Alex Eisenhut on October 28, 2014, 02:35:58 pmThe fuse in question is a glass fuse. Are these interchangable when they have the same spec? Anyway, will take a while to arrive, but as a more permanent solution "later on"... suuuure ...Might be able to find these locally however.

author: rqsall
author_rank: Regular Contributor
timestamp: October 28, 2014, 03:20:40 pm
content: Quote from: Muttley Snickers on October 28, 2014, 03:14:32 pmI'm over 40but at 125V rated, I'd rather not hack about with foil. Unregulated voltage is about 24V however... I might be able to get the non-glass replacements locally. Going to check local shops.Thank you for the replies.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 28, 2014, 04:01:30 pm
content: Quote from: Muttley Snickers on October 28, 2014, 02:57:53 pm1) He said "found some on ebay and other places, but they would take some time to arrive and they're also not cheap, especially counting shipping." so I found a part with free shipping.2) I didn't recommend anything with antimony solder.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 28, 2014, 04:06:54 pm
content: Quote from: rqsall on October 28, 2014, 03:16:39 pmMaybe, maybe not. You linked to slo-blo fuse, but is it really? Usually those are used at the mains in for the whole system, as the fuse needs to survive the inrush current when you turn on the scope. (the big caps after the main rectifier need lots of current when they're empty)A little guy at 0.5A for a local supply, I don't know if it would also be a slo-blo fuse. The power ramps up slowly at first, so I'd think it's just a regular fuse at that point.Look at your fuse, there's a bunch of stuff stamped on the metal caps. Can you show or tell us?

author: SeanB
author_rank: Super Contributor
timestamp: October 28, 2014, 04:56:25 pm
content: If those metal end caps are pressed on they can be removed to graft to a new fuse, they either will come off with a little work or with a little crunching of the whole cylinder gently with big pliers.

author: rqsall
author_rank: Regular Contributor
timestamp: October 28, 2014, 07:34:35 pm
content: Quote from: Alex Eisenhut on October 28, 2014, 04:06:54 pmI doubt it's a slow blow. The probe was only on the transistor leads for an instant. I linked to it, because of the picture that shows what it looks like. Not for the specs, sorry if that caused confusion, I should have mentioned that. The only markings on it are 125V 0.5A and the letters 'b' and 'K', each set inside a circle. Also, there seems to be a logo or so, also within a circle.... can't recognize it. Thank you for making me dig it out of my trash can, because I tossed it after I broke it trying to get the caps with the leads off

author: rqsall
author_rank: Regular Contributor
timestamp: October 28, 2014, 07:38:14 pm
content: Quote from: SeanB on October 28, 2014, 04:56:25 pmThey seem to be, but apparently I'm not gentle enough. The thing broke apart, glass all over the bench

author: rqsall
author_rank: Regular Contributor
timestamp: October 28, 2014, 07:46:10 pm
content: Anyway, thanks for the help guys. I can get fast pico fuses locally or get the one from ebay. Will take a while, but is a little cheaper...

author: SeanB
author_rank: Super Contributor
timestamp: October 28, 2014, 07:48:21 pm
content: Glass all over yes but the stepped end with a wire will come off with work. It will look like a metal end but will be made from 2 parts at each end.