Electronics > Repair

broke jumper wire?? HP 6177A. What is this failure mode?

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coppercone2:
I decided to do a extra thing where I resoldered some of the the joints on my HP6177A because it looked really crusty.I replaced alot of parts there.


There is some jumper wires, that look just like fairly thick gauge copper (18AWG) bent into little U's and soldered between pads.


One of them when heating cracked in half.

I figured this would be basically the most reliable part on the PCB. It looked fine and I saw one side sag over as soon as I melted the joints.


It seems kind of strange to me that a copper wire arch would just break like that.

What causes this kind of failure? Some kind of deep corrosion? strain? defective wire? its single strand BTW

fzabkar:
Fusible link???

coppercone2:
no the other two are fine

I would only normally expect to see this on a motor. I have seen broken wires like this on motors. I figured it had something to do with forces. but this is a low current circuit board

coppercone2:
I wonder if someone cut it before and pressed it back together with out soldering. the thing is though it looked like cleaved for a second like really well fitted before it came apart.most hand tools to cut it will leave like a really visible cut on something that thick.


Under magnification it looked kinda weird. i did a cut on the other side and my cutters leave a totally different imprint. I dunno how I could describe the geometry, it looks worn out some how. Kind of reminds me of how a thumb would look in low poly (like a tesla truck).

I think it must have cracked and corroded. Not sure if flux got on it, I wiped it down a bit on a tissue with alcohol, I think I could describe it like a patina.

Unfortunately I dropped that end into a pile of rubbish because my fingers slipped. The other side got solder on the interface when I was rotating it while the solder was molten with tweezers so that is a pain to try to clean up.


But from what I can tell, it cracked. Because the remaining geometry is too weird for any cutters.




so beware, it looks like even a humble jumper can crack on you. and i mean a nice rounded arch one, not a stamped staple thing with 90 degree sharp bends.  :o


and the board is basically fine outside the usual heat damage near some transistors.


So while the rivet, via and solder joint are suspect, don't forget to probe jumpers, as bullet proof as they look. I don't think I would have found this unless I decided to randomly touch it wiht a soldering iron to neaten it up.


ALso I applied the flux before heating the joints with a paint brush, it was a clean application, I don't have it splattering etc, so its not my flux


and yeah after writing that i renember when i first heat it, the solid form developed like a visible band on it, then that split as one half of the arch sunk into the PCB hole

it looked solid before, maybe it looked like there was a tiny nick in it. i thought it was just scratched with tweezers or something when I was moving resistors around.


the spacing between the holes is about 1/4 inch BTW


like how it looked IMO : cut a wire with side cutters, invert one side (so the triangle shaped wire mates into a triangle shaped hole). A side cutter leaves triangles on both sides. a shear makes it deform to the side and cuts strait, a super flush cutter leaves like a mow-hawk in the middle but its mostly flat. this is not the work of a cutting tool



but the red triangle is a 3d weird tesla truck shaped pyramid thing with different size faces

coppercone2:
maybe something to do with old wire that is not clean? if this can happen to a solid bus wire I am just feeling paranoid about that springy dirty copper shite we are seeing nowadays  :palm:

given that this unit has :
1) replaced boron nitride ceramic TO-3 isolators with FR4 PCB material
2) has jumpers that are cracking

It makes me think maybe HP tried to cut costs some where. I would not be surprised if the copper was some how low quality... cuz if your gonna approve FR4 heat pad over specific boron carbide, I am just getting suspicious about what other liberties that manager will take. "its still 80% copper!" :-DD

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