[Halld-tagger] wrong component

[Curtis A. Meyer]

Great catch on this!

  Curtis
-------
Prof. Curtis A. Meyer			  Department of Physics
Phone: (412) 268-2745		  Carnegie Mellon University
Fax:      (412) 681-0648		  Pittsburgh, PA 15213
curtis.meyer at cmu.edu                http://www.curtismeyer.com/





On Mar 6, 2014, at 3:00 PM, Richard Jones <richard.t.jones at uconn.edu> wrote:

> Dear colleagues,
> 
> Kudos to Alex Barnes, who has been struggling for almost two weeks now to understand the reason why our preamplifier boards have an ugly oscillation in the signal baseline at 100 kHz, as soon as we set them up and bias them for readout of fibers.  We traced the problem down to one malfunctioning component which is a voltage regulator on the preamp board that generates one of the critical dc voltages for the amplifier.  That part was generating 100kHz oscillations on our board, but they would go away under certain weird conditions, which are not compatible with actual running, unfortunately.  Chasing down the particulars of those weird conditions turned out to be a red herring.
> 
> Finally Alex decided that either all of the parts are burned out and malfunctioning in the same way on all of the boards, or else it is actually the wrong part that was installed by the manufacturer.  The second turned out to be correct.  We ordered some of the correct part ourselves from Digikey and swapped it out, and voila the oscillations are gone.  After extensive searching online, we have determined that the manufacturer installed the TLV431BSNT1G instead of the NCP100SNT1G that we specified in our parts list. This is confirmed both by the markings on the chip and by the operating characteristics. Both of these are shunt regulators, but they have reference voltages that are different by almost a factor 2.  Now that it is understood, we are back on track with setting up for QA of fibers.
> 
> -Richard Jones
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