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Re: Op amp troubles....I think?

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  • VA3XCD
    The saga here continues and I am getting more and more confused as time goes on.... I ordered a new LT6231 op amp chip from Tony and it arrived today. I
    Message 1 of 44 , May 2, 2011
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      The saga here continues and I am getting more and more confused as time goes on....

      I ordered a new LT6231 op amp chip from Tony and it arrived today.
      I soldered it in place, the correct way this time :), and went on to do the testing. I began to check the pins, both on the pads as well as at the pins. All the voltages checked out as per spec. I then went to check the values for R33 and R32. I checked the voltage on R33 first without the 10K jumper, and got a spec value. I powered down, installed the jumper, and checked the voltage, and got a value of .003 volts. I powered down, removed the jumper, powered up again and checked the voltage at R33 again and still have .003 volts. I then re-checked the voltage on the pins of U11, and got the following values:

      Pin 1 .002
      Pin 2 .218
      Pin 3 .241
      Pin 4 0
      Pin 5 .241
      Pin 6 .147
      Pin 7 .045
      Pin 8 5.018

      All units are volts.

      At this point I went back to check the values on U10 in the QSD circuit, trying to work my way back.

      I started to check the voltages on the pins. Here are the values I was getting:

      Pin 1 0
      Pin 2 2.503
      Pin 3 .129
      Pin 4 .108
      Pin 5 .101
      Pin 6 .230

      At this point I went back to check the ones I had just checked, and I dont know what happened, but they were all back in spec, just the way they were when I initially finished the stage.

      So I went back to check U11 again, and this time right up to pin 5, the values were in spec. I checked pin 6, and it had dropped back to .142 volts. I went back to check pins 1 through 5 again, and got similar very low values I mentioned above.

      So I went back even further, with intermittent spec, and bad voltages.
      I went right back to the LO circuit to check the values on the R12 and R13, and I noticed that now the si570 will not let me enter 24 MHz for a frequency for the tests. In fact it will not go above anything past 15.99 MHz now. I dont know if that is a function of the rest of the components being in the circuit, or if something is really wrong somewhere.

      At any rate, this is the stage I am at now. I think I have included all relevant info that I can think of.....

      As I mentioned in the initial post when this all started, all test values were in spec up to the point where I installed U11.
      Now the values are intermittently good and bad.
      I have also gone as far as checking all my joints, and also wiggling components to see if I could find a bad joint somewhere. I wiggled all the inductors, and most of the components and still could not nail down a reason for the intermittency.

      Any help is greatly appreciated, especially before I pull out any more of what little hair I have left :)

      73
      Bill
      VA3XCD




      --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
      >
      >
      > ----- Original Message -----
      > From: "Bill
      > Subject: [softrock40] Op amp troubles....I think?
      >
      >
      > > I was hoping to not have to embarrass myself again as I did with the
      > > quadrature
      > > clock problem I had, but here goes :)
      > >
      >
      > Don't worry about embarassment. We all run that risk, I've made some silly
      > mistakes.
      >
      >
      > > Where I run into trouble is when I check the voltages on R32 and R33.The
      > > I have the following values:
      > >
      > > R32 NO resistor : 2.570V
      > > R32 with resistor: 2.583V
      > >
      > > R33 NO resistor : 2.567V
      > > R33 with resistor: 3.85V
      > >
      > > R33 seems to be in spec, but R32 is only slightly higher with the
      > > resistor than
      > > without.
      > >
      > > I did have an issue when I originally installed U11, where the voltages
      > > were off
      > > (the 2.5V values were reading .2xxxx instead of 2.xxxx) so thinking I
      > > installed
      > > the IC backwards again, I desoldered it, flipped it around, and
      > > resoldered it.
      >
      > This looks as if reversing the IC may have damaged it.
      > If all joints are good you'll possibly have to change it.
      >
      >
      > . I did run
      > > into a
      > > similar problem with odd voltages again on U11, and found that if I
      > > power down,
      > > and power back up again, the voltages on U11 came back to where they
      > > should be.
      >
      > Note that the voltages can vary quite a bit from Robby's pages. Maybe +/-
      > 1V. They will possibly change with frequency so a restart will be on a
      > different frequency.
      >
      > > PC, loaded HDSDR and although it seems to be working in the software, I
      > > get a
      > > rather broad carrier on the centre frequency, and do not hear or see
      > > anything
      > > else other than that carrier. I do have a screen shot of what HDSDR is
      > > showing,
      >
      > If the op-amp is faulty you may not see any signals. The shot seems to show
      > problems, when you get the IC fixed lookat
      > <https://sites.google.com/site/g4zfqradio/sdr-with-soundcard-basic-faults>
      > for some clues, maybe mixer settings.
      >
      >
      > > which I will post in the files section is that will be of any help.
      > > The file name is VA3XCDHDSDRscreenshot.jpg and is located in the root of
      > > the
      > > files folder.
      > >
      >
      > Best put these in the photos folder, the file section is 99% full.
      >
      > 73 Alan G4ZFQ
      >
    • Sid Boyce
      Bring back the moving coil meter? At least when the needle gets pinned to the left end stop, pronto you d realise your leads were reversed. 73 ... Sid. ... --
      Message 44 of 44 , May 5, 2011
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        Bring back the moving coil meter? At least when the needle gets pinned
        to the left end stop, pronto you'd realise your leads were reversed.
        73 ... Sid.

        On 05/05/11 14:40, Jordan wrote:
        > Actually, I believe the Magnetic North Pole is moving closer to Russia, and
        > I also believe that regardless of what SPICE says or doesn't say, any
        > diagram showing IR drop, will also indicate the polarity, especially in a
        > dropping string, or voltage divider network.
        >
        > There is a big difference between a component being polarized and a
        > component having polarity.
        >
        >
        > 73...Jordan VE6ZT
        >
        > ----- Original Message -----
        > From: "Richard"<richard.bown@...>
        > To:<softrock40@yahoogroups.com>
        > Sent: Thursday, May 05, 2011 1:33 AM
        > Subject: Re: [softrock40] Re: Op amp troubles....I think?
        >
        >
        >> On Wed, 2011-05-04 at 22:37 +0000, dad@... wrote:
        >>>
        >>> All
        >>> I hate to sound dumd have built some, but have never heard of poliarty
        >>> on resistors. Enlighten me please.
        >>> Dave
        >>>
        >>> Sent via BlackBerry by AT&T
        >>>
        >>
        >>
        >> Hi Dave
        >> nor have I and more importantly SPICE has no knowledge of polarised
        >> resistors.
        >> If you measure a resistor with a network analyser, you see a resistive
        >> product, there is some reactive component due to manufacturing, but not
        >> enough to make any difference on HF and very little on VHF, and if you
        >> turn it around you get the same results.
        >>
        >> Maybe its something to do with the magnetic north pole being closer to
        >> Canada than anywhere else.
        >>
        >> --
        >> Best wishes / 73
        >> Richard Bown
        >>
        >> E-mail: richard@...
        >>
        >> nil carborundum a illegitemis
        >> ########################################################################
        >> Sent by Evolution 2.32.1 on Fedora FC14 x86_64 Dual core AMD Athlon 4400
        >> Ham Call:G8JVM
        >> Maidenhead QRA: IO82SP38:LAT. 52 39.720':N LONG. 2 28.171 W (degs,mins )
        >> QRV HF + VHF Microwave 23 cms:140W,13 cms:100W,6 cms:10W& 3 cms:5W
        >> ########################################################################
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        --
        Sid Boyce ... Hamradio License G3VBV, Licensed Private Pilot
        Emeritus IBM/Amdahl Mainframes and Sun/Fujitsu Servers Tech Support
        Senior Staff Specialist, Cricket Coach
        Microsoft Windows Free Zone - Linux used for all Computing Tasks
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