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Cold Solder Joint

Found this inside a friend’s dead USB memory stick:

Cold solder joint in USB memory

Cold solder joint in USB memory

The leads come from a teeny 12 MHz crystal. The solder blob on the other side looked just fine, but you simply can’t tell by looking.

As it turned out, the stick was dead for some other reason: the Flash memory controller chip got hot when the stick was drawing power. Resoldering all the joints had no effect, which wasn’t surprising.

I suspect a killer static discharge or some such calamity.

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  1. #1 by hexley ball on 2010-12-16 - 11:40

    Ah, the curse of the fractured solder joint. I just finished wrestling with one here; the auto-dimming rear view mirror in my wife’s minivan developed an intermittent temperature readout a while back and it turned out to be a bad joint.

    But that diagnosis didn’t come until it had led me a merry chase, in which I proved successively that the remote sensor was good, the wiring harness was good, and the mirror itself was good — so the thing should just work.

    Everything would work fine on the bench, or when tested separately, but when connected in stitu there was no joy.

    I finally decided it **had** to be the electronics in the mirror. Still, putting the case in the vise to start cracking the welds on the plastic case caused some serious second thoughts.

    Turned out to be a bad joint on the .156″ stake header for the power and remote sensor leads. The header is over an inch long, which means the mating connector/cable assembly can torque it quite a bit. Finally cracked a joint after 10 years.

    I should have remembered the First Law of Intermittent Electronics: it’s always a solder joint.

    • #2 by Ed on 2010-12-16 - 12:14

      it’s always a solder joint

      A-men!

      I’d claim this is as a data point in the “It’s always the connector” category, too.

      • #3 by Kuba Ober on 2013-06-26 - 21:08

        Well, either that or a 10 cent passive part killing a $500 dealer-programmable-only part :/ Alas, I’ve fixed a server that wouldn’t boot with nothing but oscilloscope and a piece of wire. It was a dead buried via, on a signal without which the Xeon CPU #0 wouldn’t run for more than apparently one cache fill. And I figured it out with nothing but a 7934 storage mainframe with a 7D11 digital delay plugin in addition to the usual hor/vert plugins. Suffice to say, as rewarding as it was, I won’t attempt that sort of a feat ever again.

        • #4 by Ed on 2013-06-26 - 21:45

          7934 storage mainframe with a 7D11 digital delay plugin

          Being able to ponder a single-shot trace for ten minutes does confer superhuman powers. Those were wonderful scopes; we had one in the lab, long ago in a universe far away, and I absolutely depended on it.

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