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

[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. 


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 

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!"

[coppercone2]

well don't judge a book by its cover, the boron nitride is there. its a fiberglass PCB cutout that protects it from edge chipping. nice feature. I thought it was a hack job but its just undocumented HP quality

[coppercone2]

well I reheated every part on the PCB and I noticed somethign funny, that is, when I heat one of the staked on resistor elevation posts for the power resistor, after lightly fluxing, ALOT of nasty aass brown foam came out of one post


I am wondering if they maybe got a bad flux or mislabeled flux or something like that. it started spewing crap like a volcano. like a brown black color

maybe that substance could have corroded the jumper wire. there was a stake resistor offset post near that jumper.I probobly should give this board a clean in Alnox before reassembly into the instrument, maybe I disturbed some acidic residues


I could see it because some of those resistors look like they are put in after assembly during testing to linearize the instrument. could have went to a non manufacturing bench for tuning where there was a desk jockey engineer that used some plumbing flux on it... they might know what linearizing a circuit is, but they might not be so keen on stupid simple assembly techniques, or maybe they just did not wash those tuning resistor posts after soldering unlike the rest of the circuit.


or i also see in the manual they say the user has to replace a resistor to change the insturment programming settings. anything could have happened there, must have been common for people to use the wrong flux for this part


you might wanna check out your rivet on resistor standoffs in old equipment for this kinda problem

[coppercone2]

well I got the bottom wires on the PCB attached just need to fix a light and add 3 stabistors then I can do the top wiring and hopefully this damn thing will work.

[coppercone2]

damn I replaced the faulty diode and transistor and all the other diodes and its still capping out at 0.5V output. These two transistors are getting hot. They measure seemingly OK on the diode test, but I cut them out anyway, and the leads look god damn char broiled.  Its the 11.8V rail, so I don't know. If I replace those, and it sitll does not work, I can do the op amp, because there is no other load on that really. q11 and q12

i suppose i can test the opa on the bread board because this thing is seriously getting out of hand. if i have to redo the wiring 1 more time ima blow a fucking head gasket

I don't like how those 2 transistors are getting hot when the only loads on them are 2 cool op amps and some high value resistors that have no buisness getting hot in the multi kohms. I think that component must be malfunctioning somehow. Unelss I suppose the op amp is basically shorted and does not make heat. i gotta check that possibilitiy.

[coppercone2]

also all the references have a very high noise level compared to the manual

I am going to replace all the transistors in the reference circuit. The zener are all new, and since the ripple is across the board, maybe the front transistors are bad.. they were cooked after all.

not even close to the manual. i did also replace the caps

[Gyro]

Maybe it was a 'cut on factory test' jumper and you just didn't notice the gap.

[coppercone2]

nah like I said the pieces come together like two ice cream cones with elon musk characteristics. no cutting tool will do that.

i looked at cuts under a microscope for wire before with everything from cheap dykes to ultra flush cutters and wire shear, none of it looked close to this. they usually leave a 'mowhawk' type thing or just crap pushed to the side with shears. this is like weird fracture

[coppercone2]

why would transistors make this reference circuit, with all new diodes and no carbon comp resistors (replaced with metal oxide) be noisy in the tens of mV range when the spec is in the 1mV or less range (100uV)? The caps are new too

I replaced everything in red.


Can the rectifier diodes be involved in the problem? I think its the transistors since they look sooty and get hot (R11, R12). Every single rail is basically noisy. I left the metal film and WW alone. The stabistor replacement is a stabistor, not a hack of many diodes. I did R28 too, I just forgot to circle it

I just wonder if maybe the transformer can be over loaded and that is creating ripple/noise (ACV measurement fail). But the DCV was all pretty close. I figure it would be really sagged if the transformer was getting beaten down

I think that maybe there is damage to the transistor that still makes it read fine on diode mode. I heard this is possible with over heated transistors.

[coppercone2]

Well i randomly got two of the cheapest transistor types to replace,

 but during work I found that of course, I forgot to solder in TWO of the leads of one of the transistors I replaced in the pair where I found a broken one. All my inspection steps missed this hole, even with bright lights... this one actually read open circuit in the diode test


So its possible I fixed the problem but missed soldering in the transistor fully, and now have to replace more transistors since I cut them off.


But it still does not explain the tested but super over heated looking transistor. 


I assumed the powerful light would reveal all the missing solder, but it seems the transistor can is just too good at blocking light. so if you do the flashlight inspection trick, make sure you renember it wont work on some large parts. I only noticed it because I  touched it and it moved.