What gets 'fried' in a wall wart!>?? usually

[analog kid]

OK, I have had three different  18-20volt dc wall wart power supplies, all of which I've been using mainly to power +15v regulators in my EH clone pedals and also my Neovibe.  The first one stopped working when ts'ing a neovibe , I assumed it grounded out to + when I had the amp off or something. overlooked it and tossed it in the bin.    Well, now my real nice 18v 1Amp supply (for a Canon camcorder) has stopped putting out vlge as well      And this time I actually saw what happened , I had a barrel plug soldered to it , uninsulated, and my son squeezed the tip/sleeve together real quick...and bam, gone no more power!
My question is, surely the transformer itself in these supplies isn't that easily blown (I desperately hope not ) so if not then will the replaceable components ,ie; 4 rectifier diodes and filtering cap... in the wall wart cause the supply to stop outputing vltg by being fried like this  WITHOUT actually hurting the transformer?   
Someone please straighten me out on this cause it's breaking my heart that i've lost two of my three large supplies   
    Thanks

[Hal]

I'd put my money on the windings of the transformer burning, unless there is a fuse.  I think its much harder to burn a diode like that, as long as they're within ratings...

[R.G.]

There is often either a thermal or current fuse buried inside the windings. The idea is to make sure that the little darlings don't become a source of ignition and burn down houses if they overheat.

If it's thermal, it may be one time or resettable. Let them cool overnight and try them again. If it's resettable, it will have reset. If not, toss it out. It's become a Darkness Emitting Diode (i.e., a DED).

[analog kid]

OH.. Really? I was really hoping against that. Since it's the SECOND TIME it's happened to me. I  have many fx that run higer than 15v now and big ps's aren't quite as common as 9v under , and I happened to come cross 3 of them, this canon the nicest.  1Amp.  It is a big heavy bugger. MUCH heavier than the other cheaper ones (both for comp monitors I think?) It has hex looking screws to open it up but I don't seem to be able to get a bite on them.   don't know if there's a chance it has a fuse then>
  So it's not gonna be the filter cap or diodes then most likely? And as far as the windings them self IF that would be the problem, it's not the type of thing you just see the break and carefully solder it Like and wah inductor  (right?)
  as it's seems to be the same thing that happened to the other cheap one , I have it apart now, I may look at the transformer on it. Should there be resistance measured on /between all and any of the transf leads?
thanks for the input

[R.G.]

Sorry. The bigger the transformer, the less likely they are to have an internal fuse.

It is a big heavy bugger. MUCH heavier than the other cheaper ones (both for comp monitors I think?) It has hex looking screws to open it up but I don't seem to be able to get a bite on them.   don't know if there's a chance it has a fuse then>

Some wall warts are not transformer based, they're actually miniature switching power supplies. These tend to be the lightweight ones though. If it's heavy, chances are there's an iron-and-copper transformer in it. The hex-looking screws are probably Torx or security Torx, designed for keeping you out.

So it's not gonna be the filter cap or diodes then most likely?

It's always possible.
Here's the rub. These power supplies are made with safety as a first factor. That's why they're hard to open up. Unless you can open it up in a way that lets you CLOSE it back up and still have a safe unit, it is simply not worth the risk. The cheapest medical help I can imagine is more expensive than a wall wart bought brand new.

If you can open it up so it can be reclosed in a safe manner - no open holes, wires hanging out, etc. it's not going to be worthwhile as a power supply IMHO. It's too dangerous.

OTOH, it's worth zero now. You lose nothing but time if you open it up destructively, and you get to see what happens in there. Just be prepared to fully junk it if you can't close it safely. I encourage you to satisfy your curiousity but only if you'll promise to junk it if it can't be put perfectly right.

And as far as the windings them self IF that would be the problem, it's not the type of thing you just see the break and carefully solder it Like and wah inductor  (right?)

Usually not. If the break happens to be on the surface, sure. But it's usually not. You can test the windings on any transformer with a DMM, a battery, a resistor and an NE2 neon bulb. The DMM set to resistance tells you if windings are open or shorted together. An internal fuse will show as an open. The battery, resistor and neon will let you find an internal short - but these are rare.

as it's seems to be the same thing that happened to the other cheap one , I have it apart now, I may look at the transformer on it. Should there be resistance measured on /between all and any of the transf leads?

Transformer leads are long lengths of copper wire. Short fat ones (i.e. low voltage windings) will have very low resistances, in the few milliohms, which show as zero ohms to a DMM. Long, thin ones (i.e. primaries in small transformers) may have up to a couple of hundred ohms of wire. You tell what's a winding by looking at where it connects. If there's clearly voltage going in (i.e. two primary wires) then the winding must not be open circuited. If the windings clearly should not connect, like a secondary and a primary, any resistance under an open circuit is an internal short.

But please, don't muck with this unless you dead absolutely certain that you can work safely - unit unplugged, of course, and knowing how to repair it properly if you find a bug - before you go in there. We don't want to lose you.

Wall warts can be had for a few bucks at a Goodwill store.

[analog kid]

Hey!! I got a proper hex wrench and opened her up. Going to go w/ the 'let it cool'  as you stated RG. And low and behold what a (hopefully not premature) relief...this thing does have a fuse 'soldered-in' right beside the diodes!! And it's blown. So is it safe to say it's wired in a way that it's ALL that will go no matter what or how hot you get it?
I will have to desolder the fuse to see what value , and if I have one as big or bigger amperage to replace it. As I don't beleve I've ever seen the end caps of a fuse used as solder pads before  I'll have fun replacing it.
Also  I did take note on this supply that it looks like a porche compared to a buik internally as well as made well externally once I got in there.    big diodes and a large 6,800 uf cap , I assume due to the slightly larger than usual 1amp current
  So am I safe , did I luck out here? This was the supply that I was planning to make use with my diy distrubution box to hopefully power every single 18v , 15v , 12v and 9v pedals that I use 

[analog kid]

Thanks RG , I read you post better and I appreciate your concern. Many people WILL go blindly into 'bad' places where they should not.... Yeah they do. I USED to be one of those people!!   I have had many close calls , big and little shocks and am probably very lucky to have not ' been lost ' already  
anyway yes I got a bite on the "HEX??" screws and they came out very easily and will be very securely retorqued into the casing. Though I did  crack the hub the bolt end of one of the 4 threads into but a bit of epoxy to put it back and I don't think that'll be a safety issue with all them holding casing
Still my biggest concern of course is that the fuse is made to be replaced (duh , I guess so or it would'nt be there as a fuse huh?!) and that getting a replacement in there will be all it needs.
 UPDATE:
I got the burned fuse out , I don't believe I have an exact replac., it seems to be a 4A 125v rather than 250v fuse.     suggestions on any other than exact repl.?? It is one of the shorter variety as well, like goes in my DMM.  I didn't know if a 4A larger size and bigger 250v value fuse would be adequate for the purpose so long as space permitted?

[jrc4558]

There is often either a thermal or current fuse buried inside the windings. The idea is to make sure that the little darlings don't become a source of ignition and burn down houses if they overheat.

If it's thermal, it may be one time or resettable. Let them cool overnight and try them again. If it's resettable, it will have reset. If not, toss it out. It's become a Darkness Emitting Diode (i.e., a DED).

RG, could I borrow that DED abbreviation for naming some distortion build? Its too cool.

I usually find that in cases with BOSS power supplies, voltage regulators live fast and die young.

[R.G.]

I got the burned fuse out , I don't believe I have an exact replac., it seems to be a 4A 125v rather than 250v fuse.     suggestions on any other than exact repl.?? It is one of the shorter variety as well, like goes in my DMM.  I didn't know if a 4A larger size and bigger 250v value fuse would be adequate for the purpose so long as space permitted?

You're in luck!

A 4A 250V fuse is a fine replacement for a 4A 125V. There will be some lettering on the fuse. Can you eagle-eye that and post it here?

Fuses come in various blowing speeds. You want to match what it had in there. The lettering on the end caps may tell the type.

[R.G.]

could I borrow that DED abbreviation for naming some distortion build? Its too cool.

Be my guest. I didn't come up with it. I first heard it in about 1975.

[Paul Perry (Frostwave)]

I believe that (at least in Australia) it is illegal to have a replacable fuse in a plugpack.
If I was worried about plugpacks burning out thru shorting or overloading, I would put an external fast fuse in the output.
Switch mode power supplies are likelier to die from mains surges.

[analog kid]

Ok, the original small fuse that burned is 125v 4A  and has "SLA" noted on the cap , but the only 4A 250v fuse that I have on hand has the listing BUSS "MDL"  on it.       w/o knowing, I guess that the original little fuse is of a faster blow speed than the larger 250v that I have. ? ?It is gonna be alot taller in there but who'll ever see it, and it's beside the big filter cap and about the same height so if it will work no prob there.     Is this an alright replacement fuse for this supply (or SAFE) I mean if there is ANY question it would be a bad or dangerout fuse replacement I'm sure it isn't too hard to  go find the exact replacement locally, on the other hand . . . If this will work fine...
Just let me  know asap and I'll be confident in your appoval of the fuse

ps; as for Frostwave's legality comment... I guess this doen't mean that doesn't  hold true in the US as well ? I don't know since I don't know if fuse that's heat shrunk and soldered in rather than easily swappable fuse clips would be considered a "replaceable fuse" But this supply was obvioulsy made to open and reclose fairly simply for a reason.

[grapefruit]

Often time delay fuses have a T after the amp rating. Not sure what the "SLA" means.
Buss is a brandname. "MDL" is a slow blow type fuse for that brand.
If the fuse is still kind of intact: if it looks like a spring, or has a bead in the middle of the wire, it's probably a slow blow. If it just looks like a piece of wire it's probably fast blow.


Stew.

[analog kid]

Thanks, yeah I always figured the "buss" fuses were just the brand but I typed lettering as it was.  Anyway If "SLA" doesn't give any info on blow speed than there isn't any cause aside from that (on the original blown fuse) all that's there is ' 4A 125v'   The actual fuse itself in the glass , though blown, is of course much thinner than that in the 250v replacement I will likely use. just how much of that is only a difference in volt.rating is what I wonder.  because the new only 4A fuse I have is as I said listed 4A 250v and 'MDL' rather than sla. AND the fuse in it is big looks about just like a low E string on a 6 string
I hope this will be alright. It's installed in the supply now but not been applied power to yet

[grapefruit]

The fuse you've put in is slow blow. This should be ok. If the fuse is gonna blow it's gonna blow anyway. Slowblows are used when there are large surge currents, like for the primary fuse on a toroidal transformer.


Stew.

[RDV]

Just insulate them wires you know. I've had a few 30v @ 3A explosions in the last year and it's not pretty. I blew my perfed LM3886 amp cause of a charged heatsink. It was loud and violent and smelled bad. I now insulate everything.

RDV

[analog kid]

Thanks, Yes I have the new fuse insulated as well as the one that was in there. Only thing is the fuse being 250v and twice as large is that I couldn't fit the heavy duty pvc tubing that was covering the small fuse back over the new one, So I had to just cover it with a length of regular old black heatshrink. it's in there like a standing up resistor so only one of the soldered on wire leads has to be insulated.  Should this be ok? I guess they used that heavy tubing for safety.
I still haven't powered it up yet.  Fingers crossed.
Since this is a really nice 1A supply I think I'm gonna hold off using it on indiv pedals around the house and wait til I get my little distribution box with sockets and  power patch cables... using filtering and reglulators inside for +15, maybe +12,and for sure +9v  to hopefully power ALL my fx with!!  And try not to chance damaging anymore due to shorting + to ground etc...  maybe I'm just careless

[analog kid]

update:
In case anyone wanted to know. The 250v 4A fuse seems to be holding up fine at least I was lucky enough on this occasion that was all the damage done. Hopefully w/ this ps if anything would ever happen AGAIN that's all that will ever go.     So all good and well , Now just need to pick up some more regulators and make my distribution box for running my 18v, 15v and 9vlt effects all by this one powersupply!   This is a 1A so it should power about all I need.   anyone know if there's any reason I'd need to use 1A regulators in my distribution box since the powersupply powering them is 1Amp??or does it matter and 100ma 's will hold up fine?
ALSO I did install a new barrel jack on the end AND reverse the pos tip to a Negative Tip /Pos sleeve for use with  most of my pedals and so I can run PS And Batteries with 3pin DC jacks.

[Paul Perry (Frostwave)]

A 100mA reg is fine.. IF you only want to get 100mA otut of it, and don't mind it running flat out. Since the 1 A flat regs don't cost any more, I'd use them. Just be careful not to short the metal case against anything.

[AzzR]

I had one start smoking while still in the wall, Opened it and a diode had fried.

-Dream