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RXTX Ensemble TX OpAmps Question

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  • CJ McKinney
    I made it to the TX OpAmp installation stage of the Ensemble RXTX (20/30/40m option), where all tests in stages prior to this were fine. Upon testing the TX
    Message 1 of 8 , Sep 22, 2012
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      I made it to the TX OpAmp installation stage of the Ensemble RXTX (20/30/40m option), where all tests in stages prior to this were fine.  Upon testing the TX OpAmps U6 and U7 I found an issue with the voltage.  Where I should be showing 2.5V or 5V on both ICs pins except pin 4, I am only getting 2.15V and 4.3V.  Further on the Left IC pin 6 only shows 1 volt and 7 shows no voltage.  I am unable to see any isues in general that would explain these low voltages.  Has anyone had this experience and have any suggestions for bringing the TX OpAmps up to specifications?
       
      Thanks,  --CJ
    • KF4BQ
      ... Hi CJ, The 2.15 and 4.3 may not be a problem. The 4.3V comes from the 5V regulator U9; you can check the voltage there too. The regulator could be loaded
      Message 2 of 8 , Sep 23, 2012
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        --- In softrock40@yahoogroups.com, CJ McKinney <cj.mckinney@...> wrote:
        > Where I should be showing 2.5V or 5V on both ICs pins except pin 4, I am only getting 2.15V and 4.3V. Further on the Left IC pin 6 only shows 1 volt and 7 shows no voltage. I am unable to see any isues in general that would explain these low voltages. Has anyone had this experience and have any suggestions for bringing the TX OpAmps up to specifications?
        >

        Hi CJ,

        The 2.15 and 4.3 may not be a problem. The 4.3V comes from the 5V regulator U9; you can check the voltage there too. The regulator could be loaded down if the current draw is very high.

        Withe the Left IC pin 7 having low voltage: check that pin 7 or following cap doesn't have a short to ground. The other possibility is that the feedback resistor (R23 or R24) is not connected properly.

        73, Mike Collins KF4BQ
      • kc0jm
        Thanks Mike for the advice. I decided to start with the power supply and work from there. At the D4 hairpin I got 12.9V, with 6.2V at the R52 hairpin, both of
        Message 3 of 8 , Sep 23, 2012
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          Thanks Mike for the advice.

          I decided to start with the power supply and work from there. At the D4 hairpin I got 12.9V, with 6.2V at the R52 hairpin, both of which seem acceptable. At the pin 3 of U9, I get 4.4V, but cannot see any obvious reason at this point for the voltage to be brought down. At U6 I get the 4.3V on pin 8 and the 2.15V on all other pins except 4 which is 0V, further I get the 2.15V at R15, R16, R21, R17, and R23, with 1.9 at R25. At U7 is where I still see the issue with voltages of 4.3V at pin 8 and 2.15 at pins 1,2,3, and 5, with 0 at 8. At pin 6 I get 1.1V and at pin 7 I get the 0V. Further R18, R19, and R20 show the 2.15V, with R24 showing the 1.1V and showing R27 showing no voltages. I cannot find any shorts or soldering issues at the pins or the components in the circuit for U7. Since I cannot find anything wrong with the circuit myself, I am leaning towards the opamp being bad. Since I am not familar with the OpAmp IC, Are there any procedures I can follow to determine if the OpAmp is bad, or am I just better off replacing it to make that determination? If there is any further advice on items I could also check to rule out other issues that would be great. Thanks, --CJ

          --- In softrock40@yahoogroups.com, "KF4BQ" <mikecol@...> wrote:
          >
          > --- In softrock40@yahoogroups.com, CJ McKinney <cj.mckinney@> wrote:
          > > Where I should be showing 2.5V or 5V on both ICs pins except pin 4, I am only getting 2.15V and 4.3V. Further on the Left IC pin 6 only shows 1 volt and 7 shows no voltage. I am unable to see any isues in general that would explain these low voltages. Has anyone had this experience and have any suggestions for bringing the TX OpAmps up to specifications?
          > >
          >
          > Hi CJ,
          >
          > The 2.15 and 4.3 may not be a problem. The 4.3V comes from the 5V regulator U9; you can check the voltage there too. The regulator could be loaded down if the current draw is very high.
          >
          > Withe the Left IC pin 7 having low voltage: check that pin 7 or following cap doesn't have a short to ground. The other possibility is that the feedback resistor (R23 or R24) is not connected properly.
          >
          > 73, Mike Collins KF4BQ
          >
        • Alan
          ... Subject: [softrock40] Re: RXTX Ensemble TX OpAmps Question ... No, 6V2 is not acceptable. ... This MUST be 5V What current is taken from the 12V supply? Is
          Message 4 of 8 , Sep 23, 2012
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            ----- Original Message -----
            Subject: [softrock40] Re: RXTX Ensemble TX OpAmps Question


            > I decided to start with the power supply and work from there. At the D4 hairpin I got 12.9V, with 6.2V at the R52 hairpin, both
            > of which seem acceptable.

            No, 6V2 is not acceptable.

            >At the pin 3 of U9, I get 4.4V,

            This MUST be 5V
            What current is taken from the 12V supply?
            Is U9 hot?
            Is R52 correct?

            73 Alan G4ZFQ
          • kc0jm
            ... Thanks for the added information Alan, I was focusing on the U7 OpAmps pins 6 and 7, but should address the voltage issue first. My current reads at 98mA
            Message 5 of 8 , Sep 24, 2012
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              --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
              >
              >
              > ----- Original Message -----
              > Subject: [softrock40] Re: RXTX Ensemble TX OpAmps Question
              >
              >
              > > I decided to start with the power supply and work from there. At the D4 hairpin I got 12.9V, with 6.2V at the R52 hairpin, both
              > > of which seem acceptable.
              >
              > No, 6V2 is not acceptable.
              >
              > >At the pin 3 of U9, I get 4.4V,
              >
              > This MUST be 5V
              > What current is taken from the 12V supply?
              > Is U9 hot?
              > Is R52 correct?
              >
              > 73 Alan G4ZFQ
              >

              Thanks for the added information Alan, I was focusing on the U7 OpAmps pins 6 and 7, but should address the voltage issue first. My current reads at 98mA from the power source. U9 is not hot, and I did reverify the voltage going in is 6.2V (R52) with 4.4V on the output. Tracing the power circuit I cannot find any bad solder joints, shorts, or solders to ground. I am not sure what is causing the excess current, as this is a change I believe after I put in the TX OpAmps. Further I now find the voltages are off on the RX ICs also, which were within specifications at the testing phase. I will continue searching, as I am sure there is something small I have overlooked. Any suggestions for further testing would be appreciated. 73, -CJ
            • Alan
              ... Subject: [softrock40] Re: RXTX Ensemble TX OpAmps Question ... Something is dragging the 5V line down. The voltage is being limited by R52. Check both
              Message 6 of 8 , Sep 24, 2012
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                ----- Original Message -----
                Subject: [softrock40] Re: RXTX Ensemble TX OpAmps Question


                >> 73 Alan G4ZFQ
                >>
                >
                > Thanks for the added information Alan, I was focusing on the U7 OpAmps pins 6 and 7, but should address the voltage issue first.
                > My current reads at 98mA from the power source. U9 is not hot, and I did reverify the voltage going in is 6.2V (R52) with 4.4V on
                > the output.

                Something is dragging the 5V line down. The voltage is being limited by R52.
                Check both op-amps are installed correctly.
                If so carefully lift pin 8 of one, then the other. See if that gets your 5V back.

                73 Alan G4ZFQ



                Tracing the power circuit I cannot find any bad solder joints, shorts, or solders to ground. I am not sure what is causing the
                excess current, as this is a change I believe after I put in the TX OpAmps. Further I now find the voltages are off on the RX ICs
                also, which were within specifications at the testing phase. I will continue searching, as I am sure there is something small I
                have overlooked. Any suggestions for further testing would be appreciated. 73, -CJ
                >
              • kc0jm
                I lifted pin 8 on U7 and found that all of the voltages went back to specification. I ordered a new Opamp from Mouser and replaced the part. I then got the
                Message 7 of 8 , Nov 2, 2012
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                  I lifted pin 8 on U7 and found that all of the voltages went back to specification. I ordered a new Opamp from Mouser and replaced the part. I then got the 2.15V on pins 6 and 7 of U7 (where I was getting nothing previously), but the voltage is still being pulled down and my current still reads above 90mA. Rechecking components along the 5V power line I cannot find any obvious problems to cause the increased current and decreased voltage. Though I am continuing to investigate, are there any further suggestions for tracking the down the culprit? Thanks,

                  73, CJ KC0JM

                  --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
                  >
                  >
                  > ----- Original Message -----
                  > Subject: [softrock40] Re: RXTX Ensemble TX OpAmps Question
                  >
                  >
                  > >> 73 Alan G4ZFQ
                  > >>
                  > >
                  > > Thanks for the added information Alan, I was focusing on the U7 OpAmps pins 6 and 7, but should address the voltage issue first.
                  > > My current reads at 98mA from the power source. U9 is not hot, and I did reverify the voltage going in is 6.2V (R52) with 4.4V on
                  > > the output.
                  >
                  > Something is dragging the 5V line down. The voltage is being limited by R52.
                  > Check both op-amps are installed correctly.
                  > If so carefully lift pin 8 of one, then the other. See if that gets your 5V back.
                  >
                  > 73 Alan G4ZFQ
                  >
                  >
                  >
                  > Tracing the power circuit I cannot find any bad solder joints, shorts, or solders to ground. I am not sure what is causing the
                  > excess current, as this is a change I believe after I put in the TX OpAmps. Further I now find the voltages are off on the RX ICs
                  > also, which were within specifications at the testing phase. I will continue searching, as I am sure there is something small I
                  > have overlooked. Any suggestions for further testing would be appreciated. 73, -CJ
                  > >
                  >
                • Alan
                  ... Subject: [softrock40] Re: RXTX Ensemble TX OpAmps Question ... So the 5V line is still 4V4? The voltage across R52 is consistent with 90mA drawn from the
                  Message 8 of 8 , Nov 2, 2012
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                    ----- Original Message -----
                    Subject: [softrock40] Re: RXTX Ensemble TX OpAmps Question


                    >I lifted pin 8 on U7 and found that all of the voltages went back to specification. I ordered a new Opamp from Mouser and replaced
                    >the part. I then got the 2.15V on pins 6 and 7 of U7 (where I was getting nothing previously), but the voltage is still being
                    >pulled down and my current still reads above 90mA. Rechecking components along the 5V power line I cannot find any obvious
                    >problems to cause the increased current and decreased voltage. Though I am continuing to investigate, are there any further
                    >suggestions for tracking the down the culprit?

                    So the 5V line is still 4V4?
                    The voltage across R52 is consistent with 90mA drawn from the 5V line.
                    Measure the resistance from the 5V line to ground with no power. I'd guess this should not be less than about 1K.
                    If it is less look at your resistor values.
                    If it is more then check all voltages bearing in mind they will likely be proportionally lower than nominal.
                    If nothing obvious shows up try lifting the pins giving 5V power to each of the ICs as you did on U7.

                    Hopefully that should give us something to work with.

                    73 Alan G4ZFQ
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