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  • EEVblog #401 – Lecroy 9384C Oscilloscope Repair – Part 2

    Posted on December 21st, 2012 EEVblog 10 comments


    Dave brings out the big guns in this attempt.
    Can a $12K Flir E60 IR Thermal Camera find the fault?
    Once again, a “real-time” attempt to find the short on the Lecroy mainboards 3.3V rail.
    Part 1 is HERE

    Flir Cameras
    ULIRVision IR Camera

    Forum Topic HERE

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    • f4eru

      Try if it is functionnal in that state.
      The asics may be damaged, but still functionnal
      In that case all you need to do is mount a bigger supply.

    • nasos

      Why dont you try to desolder the second asic and measure again the resistance and the current.
      Also maybe the oscilloscope can work with out this chip just leaving one channel off… I suggest that this chip will be demultiplexer or triggering circuit of thiw channel.

    • Manwolf

      Use IR from cold start on each asic to see which heats fastest.

      • http://www.eevblog.com EEVblog

        They heat up the same.

    • Bismarck

      It can be helpful to replace cables from PS with much ticker ones and solder it directly from bottom side of power connector. Also rise the voltage from 3,2 volts to 3,5 volts, this voltage will not hurt but it will show more directly where is most power dissipation (non broken asics will dissipate almost the same, but broken one will dissipate much more than now.
      Desoldering second asic is also OK, or maybe you can only desolder one or two supply pins on this asic?
      Croatian bloke

    • http://www.siliconchip.com.au Nicholas

      My guess is that the PSU failed on the 3.3V rail and this caused current to flow from a higher voltage rail (likely 5V) into the 3.3V chips and damaged them. It is of course possible that it happened the other way around as you supposed but my suggestion would better explain the apparantly widespread damage.

      Also the fact that that one chip gets very hot if you power some rails and not others suggests that the unit is not designed to survive such a condition.

      • PeterK

        I have to agree with Nicholas,

        When the 3.3V rail failed it took the ASICs with it. You should pop open the power supply and see where the failure is on the 3.3V rail. This will tell you if a higher voltage spike could have been applied during failure.

    • Nick

      Maybe you could try putting the board in a reflow oven for a few minutes or use your Atten hot air station and heat up the ASIC modules. It could be a tin-whiskers problem.

    • Zeke

      No you don’t.

      Don’t throw in the towel Dave. If it is the ASICS, replace them. It would be great PR for the manufacturer to pony up some chips. If they require purchase, I’ll pitch in if you are short on dough.

      There are 80 year old grandmas in China that could whip those suckers out and replace them, blindfolded.

      Tenacity is your game. Stick to it. Rooting for you!

    • http://hackedgadgets.com Alan Parekh

      That is one heck of a nice IR camera . It looks like cheating when I think of the way I do it with my calibrated finger tips. :)