Passive component failure modes

Discussion in 'General Electronics Chat' started by Jojo_B, Nov 25, 2009.

  1. Jojo_B

    Thread Starter New Member

    Nov 17, 2009
    17
    0
    Hello,

    First of all, I discovered this forum a couple months back and I am completly impressed by the level of helpfulness and intelligence the forum contributors have.

    My question is out of curiocity, I am wondering what "most common" state most components go to when they fail (either from burning up or maybe other factors like Heavy Ion damage, ESD or otherwise).

    For instance:

    If I burn up a resistor, most commonly does it act like a short offering no resistance. Or if I burn up a capacitor, does it fail to charge acting as an open? Actually I'm not just interested in passive components, maybe µCs fail in outputs being put in indeterminate states. Please share any stories you may have in troubleshooting circuity.

    Thanks (I know this is a broad question).
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Resistors usually fail by going high resistance or open when overloaded, but there are many types of construction and some may possibly short.

    Capacitors may go short circuit if overvoltaged (so the insulation breaks down), but electrolytic caps can burst or explode under some conditions - sometimes known as a 'confetti generator' as bits of shredded paper dielectric fly everywhere.. They also smell terrible!
    With plain old age, the electrolyte may dry out and the capacitance reduces dramatically.

    Tanatlum capacitors may short out or explode.

    Power ICs, voltage regulators etc. can sometimes pop the encapsulation if they experience a severe overload.

    The majority of semiconductor failures are silent and invisible, though.
    They can be from many causes, one of the commoner ones in old equipment is simply thermal cycling - different materials have different rates of expansion, and over time the various joints and junctions can crack, allowing moisture to enter or causing a direct circuit break.

    Semiconductors running excessively hot can also fail early as the dopants that form the P and N elements migrate and effectively destroy the IC structure. This was a very common problem with some early MOS technologies, but with some of those it even happened at room temperature.

    The standard method of rapid aging electronics to predict component life expectancies is just to run them hot - it reduces the life dramatically.

    Speaking of which:
    Don't forget to check your PC fans and that the heatsink fins are clear of dust!
    Some makers no longer fit motherboard sounders, so overtemp alarms don't work. I've seen two machines with dead CPUs due to dust-clogged heatsinks in the last few weeks.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I have seen resistors and capacitors fail both open and shorted. Same with semiconductors. The topic is broad.

    Stories can be quite odd. At a naval installation in Dam Neck, Virginia, I encountered a Univac 1206 computer that would not boot on occasion. The bootloader code was hardcoded as physical wire jumpers.

    The cure was to turn off logic power, leaving on the cooling fans. Then, you said something nice to the computer. It would boot after that.

    At the school on Mare Island, the troubleshooting computer (this one was a 1208) had many residual problems. The instructors used tape to blank off pins in the circuit boards in order to cause failures. The gum did not always come off the pins, so the computer could be very flakey.

    The head instructor there was a really big guy. He had a chart. Essentially, a failure of one sort could be cured (temporarily) by opening the doors and kicking the computer in the correct location, from the chart. That worked.

    Same thing on a Hughes display console. The X - Y counting got messed up, and displacement stairstepped, instead of going smoothly. A kick on the side of the logic cage worked for weeks to months.

    Also at Dam Neck, a Sylvania-built 1208 computer had a failure in which the multiply/divide sequencer timing chain would start to run at when not executing such an instruction. We found it was started when bit 29 in the U (instruction) register got set. The only element in common between the cards (both 4020 flip flops) was that they shared the same indicator driver card. The state of all register bits were shown using neon indicators on the maintenance panel.

    Nothing turned up in the wiring. The cure (also temporary) was to swap the 4020 card at row A14 and B12 with 4020's from different locations. This always got the computer back up, and was good for several months. We penciled a swap list inside the door to insure "fresh" substitute cards would be used.

    I just had a problem with a cheapo DVD player. It would take a long time to open the movie and get started.

    There was a slightly swollen capacitor in the power supply, that was tiny and rated for 10,000 uF at 10 volts. Replacing it with a 470 @ 25 works fine. I used that one as it was the only radial cap I had that would fit in the space available. I would suppose the original capacitor was mostly open.

    Everyone has hours of tales about unlikely problems and less likely cures.
     
  4. creakndale

    Active Member

    Mar 13, 2009
    68
    7
    My experience has been...
    Resistors open.
    Capacitors short.

    creakndale
     
  5. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    I've seen resistors decrease in value and increase in value. Resistors that decrease in value can exceed their power rating and quickly go from "lower resistance" to "open resistance".

    I've seen capacitors that increase in value and decrease in value. I've see ESRs mainly increase. That typically would happen in electrolytics where the electrolyte had dried up. I replaced quite the number of capacitors in a Satellite receiver once.
    The ESR meter is a great troubleshooting tool, of course the same was said for building an octopus to connect to your oscilloscope.
     
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