op-amp problem

Discussion in 'The Projects Forum' started by Blackbull, Sep 8, 2008.

  1. Blackbull

    Thread Starter Well-Known Member

    Jul 26, 2008
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    http://s431.photobucket.com/albums/qq34/zingro/?action=view&current=op-amp3.jpg

    I breadboarded the above circuit, it worked well so I built it up. It amplified 50uV to 35mV and stuck there. I re-built it again with a new op-amp. The only reading on the meter was 0.1mV and a change of polarity. the op-amp was hot to the touch. I'm confident all the joints are good and to the drawing. Has anyone a cure for manic depression?
     
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Looks Ok. What op-amp are you using?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    OK, let's pause for a moment - it WAS working well on the breadboard. This is a very important point.

    [eta] LT1007CN8 op amp, right?

    So ask yourself, "What has changed between the breadboard version and now?"
    Sounds like this time around, you have discovered yet another way to wire up a circuit that is not quite the same as what was breadboarded. The op-amp getting hot is not a good sign.
    I do not share in that confidence, I'm afraid. As a matter of fact, I'm quite certain that you either mis-wired something, or managed to somehow damage a component when attempting to "re-build" the circuit.
    Keep a stiff upper lip, old chap. :)
    Everyone makes mistakes when they're first building circuits, and it's not just the "newbies" that make mistakes. I have let the "magic smoke" out of more than my fair share of components, and occasionally even still make mistakes. I committed a quad op amp to a rather spectacular firey death just a couple of months ago, in fact. :eek: :rolleyes: It had been quite a while since I'd seen a jet of flame from the side of an IC that was that long. I now have an unusable section in a rather expensive breadboard as a reminder of my foolishness.

    Take a break, and walk away from it for a few hours. Think about something completely different. Come back when you're refreshed. The error might be simply a very small strand of wire shorting something out, or a splash of solder somewhere you can't see well.

    Try going back to the breadboard, where you did have success. Don't try to make things too crowded. Make sure your batteries are still good.
     
  4. Blackbull

    Thread Starter Well-Known Member

    Jul 26, 2008
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    Thanks folks- feel better already!
     
  5. Blackbull

    Thread Starter Well-Known Member

    Jul 26, 2008
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    I say you fellows, one would require a jolly stiff upper lip to admit to such a chumpish failure of the cranium. ( English gentleman )
    The first construction, maybe,was damaged by poking round with an analogue meter after the IC was inserted.This was on a three hole segmented stripboard.
    I thought it more convenient to use one with full strips,on the second,but overlooked cutting the tracks between the op-amp pins!!! ( should develop an interest in cricket instead of electronics ) !!!
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Well, goodonya for finding the problem! :)

    You were probably getting tired (along with being frustrated) by the time you were trying the 2nd build-up. Now that you've had a respite from it, I'll bet the problem just seemed to jump right out at you.

    Just take it nice and slow, and be sure to double-check everything before you apply power.
     
  7. RiJoRI

    Well-Known Member

    Aug 15, 2007
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    Have you considered writing a monograph on the utilization of integrated circuits as flamethrowers? :eek:

    I must admit I have never seen that effect!

    --Rich
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    It was an LM348N, which many of you know is a quad 741 op amp.

    I'd flipped the breadboard around several times, been interrupted several times, and I didn't bother to do a final check before applying +/-12v, which I happened to connect up in reverse. :eek: As one might imagine, things went downhill rather quickly upon application of power. As the silicon substrate reached the boiling point, a great deal of pressure was generated inside the poor little plastic IC enclosure, a "bang" was heard and a jet of blue flame perhaps 1 1/2" long spewed fourth horizontally from the vicinity of either pin 4 or pin 11, I don't recall offhand. The jet of flame was so hot that in the brief moment it was active, it actually started to melt the plastic of the breadboard.

    I pried the IC out of my now somewhat-toasted breadboard and rather unceremoniously tossed it in the trash can.

    I'm sure that it would warm AudioGuru's heart to know that there was one less 741-type opamp polluting his earth. ;)
     
  9. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
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    Yeah it's all too easy to get blase about temporary connections.

    I was recently fixing a vintage Pioneer amplifier - one channel down.

    Tested the power amps as OK
    Traced and fixed the fault as a dead capacitor in one of the preamp boards.

    Then kicked and half pulled out my temporary wiring to some test speakers. ~this shorted the cans of the output 2SC1080s to chassis, which joined Wookies' 348 in the trash.

    That's why we keep stock components.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    I am glad you burnt a lousy old 741 type opamp.
    I have used hundreds or thousands of opamps and I have never blown one.
     
  11. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Clearly you are good at this stuff. Perhaps you will lend your experience & expertise to positive & relevant suggestion for this topic? What techniques or procedures do you use to insure the survival of your thousands of op-amps? By what methods have you achieved your illustrious record? Teach us, please, that we may all learn from your unparalleled example.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    He's trying to keep his "Frequent Fryer" miles down. :eek: ;)

    Let's face it - if someone won't admit to at least a few good "meltdowns" during their time in Electronics, they are either lying about it, or weren't pushing the envelope. ;)

    There are plenty of "safe" designs floating around. The military is confounded between "bleeding edge technology" and "absolute reliability". They want both.

    This is why digital electronics is so affordable nowadays; indeed the computers we're using to make these posts.

    The F-22 fighter is controlled by a dual 700MHz RISC processor that's contained in a package about the size of a breadbox. For those of you who don't know what a breadbox is, it's about 1 1/2 feet wide, 1' tall, and 1' deep. 700MHz might seem slow today, but it was developed in the early 1980's, when the fastest PC's available had 386 CPUs and 4MB memory.

    Mainframe computers had 16MB RAM storage. The F-22 had more storage than a mainframe, and was faster. The programs for the prototype YF-22 computer were written in ADA. I had the privelidge of working on the wire-wrapped backplane of the prototype computer. Since this was nearly a quarter century ago, I recall very few of the details. I do know that a number of photos were taken of it; I assisted in setting them up. We'll probably never see them published though.
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    I have never connected the power supply pins of an opamp with backwards polarity like many NOOBs who didn't read the datasheet. I read the datasheet first.

    I have never connected an input voltage higher than the max allowed on the datasheet.
    I have never overloaded the output of an opamp so it smokes.

    The datasheet for a part and its application notes tell you all about it and how to keep from blowing it up.

    Survival? Illustrious record? Unparalleled example? No, just common sense.
     
  14. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Audioguru, in addition to common sense (which is always admirable), I invite you to exercise some tact. You may never have been a "noob" but many of our mebers are. You may never have chosen to indulge in electronics as a hobby instead of a serious study, but many members here do so regularly. Our forum rules require courtesy toward the "noobs" from you. Please comply with these rules.
     
  15. chrissyp

    Active Member

    Aug 25, 2008
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    Am i reading your circuit correctly? . you have 9v+ and 9v- going to pin 3 of the op amp!!
     
  16. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    The point between the batteries is a common reference. Pin 3 is actually at 0v, pin 7 at +9V, and pin 4 at -9V.
     
  17. chrissyp

    Active Member

    Aug 25, 2008
    82
    10
    Hi
    I agree with you statement , until the switch is closed , then +9v goes to pin 3.
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    When I was discourteous by saying that many NOOBs don't read the datasheet then I am sorry. If the NOOBs can't read then I am also sorry.

    I hope that NOOBs learn from my posts. Then they will read the datasheet or learn how to read.
     
  19. thingmaker3

    Retired Moderator

    May 16, 2005
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    Hmmm... looks like the lower battery and the switch are on the wrong side of each other...
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    Well, if the switch is open, there is no current path, so the V- supply of the opamp will settle at 0V relative to the rest of the circuit, and the battery voltage will be dropped across the open switch contacts.

    While it may be preferable to have the battery on the other side of the switch just for consistency's sake, in actuality it will work either way.
     
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