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Ensemble RXTX Help

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  • petewk8s
    I am building the RXTX and just completed the RF IO section. I am building section by section with the exception that I have pre-installed the surface mount
    Message 1 of 10 , Jun 13, 2014

      I am building the RXTX and just completed the RF IO section. I am building section by section with the exception that I have pre-installed the surface mount ICs. My question concerns a voltage measurement at the Hairpin of R62. The documentation calls for a measurement of about 2 volts DC but I am seeing about 0.875 VDC. I do see 2.1 VDC very, very briefly as I start the measurement then it drops to the .8.  Would this be expected at this point since I do have a load (the ICs) on the 5 volt rail? I can find no obvious shorts and component value and placement appears correct. 

      Any advice?


      Pete WK8S

    • warrenallgyer
      A definite problem Pete. There are only high impedace loads at this point and this is a simple voltage divider. Double check the values of R61 and R62. Then
      Message 2 of 10 , Jun 13, 2014
        A definite problem Pete. There are only high impedace loads at this point and this is a simple voltage divider.

        Double check the values of R61 and R62. Then measure pins 3,6,11, and 12 on U10. A low resistance to ground would be an indicator of a short under U10.

        Warren Allgyer
        9V1TD
      • Alan
        Original Message ----- Subject: [softrock40] Ensemble RXTX Help ... . I do see 2.1 VDC very, very briefly as I start the measurement then it drops to the .8.
        Message 3 of 10 , Jun 13, 2014
          Original Message -----
          Subject: [softrock40] Ensemble RXTX Help


          >I am building the RXTX and just completed the RF IO section. I am building section by section with the exception that I have
          >pre-installed the surface mount ICs. My question concerns a voltage measurement at the Hairpin of R62. The documentation calls for
          >a measurement of about 2 volts DC but I am seeing about 0.875 VDC
          . I do see 2.1 VDC very, very briefly as I start the measurement then it drops to the .8. Would this be expected at this point
          since I do have a load (the ICs) on the 5 volt rail? I can find no obvious shorts and component value and placement appears correct.

          Pete

          Yes, I think this is normal if you install all the ICs, there is certainly one reading that does not agree if you do not use
          established procedure.

          Warren,

          If you look at the IC datasheet I think it shows a diode (protection?) on the inputs which most likely drags this voltage down.

          73 Alan G4ZFQ.
        • warrenallgyer
          Alan I don t see the diode protection on the data sheet and, if it is there, how does the input ever go high? If R61/62 are correct then 4 ma.+ of current is
          Message 4 of 10 , Jun 13, 2014
            Alan

            I don't see the diode protection on the data sheet and, if it is there, how does the input ever go high?

            If R61/62 are correct then 4 ma.+ of current is going somewhere. 0.8 volts looks suspiciously like a forward biased diode, I agree. But it is not hanging together for me when I look at the schematic.

            Warren Allgyer
            9V1TD
          • Alan
            Original Message ----- Subject: Re: [softrock40] Ensemble RXTX Help ... Warren, I m not sure if anything appears in the data sheet but that s what happens. 73
            Message 5 of 10 , Jun 13, 2014
              Original Message -----
              Subject: Re: [softrock40] Ensemble RXTX Help

              >
              > I don't see the diode protection on the data sheet and, if it is there, how does the input ever go high?
              >
              > If R61/62 are correct then 4 ma.+ of current is going somewhere. 0.8 volts looks suspiciously like a forward biased diode, I
              > agree. But it is not hanging together for me when I look at the schematic.
              >

              Warren,

              I'm not sure if anything appears in the data sheet but that's what happens.

              73 Alan G4ZFQ
            • warrenallgyer
              I have to be missing something or misunderstanding Alan. If that is the case, how does the input ever develop +2.5V? Warren Allgyer 9V1TD
              Message 6 of 10 , Jun 14, 2014
                I have to be missing something or misunderstanding Alan. If that is the case, how does the input ever develop +2.5V?

                Warren Allgyer
                9V1TD
              • Alan
                https://groups.yahoo.com/neo/groups/softrock40/conversations/topics/49291 Original Message ----- From: allgyer@gmail.com [softrock40]
                Message 7 of 10 , Jun 14, 2014
                  https://groups.yahoo.com/neo/groups/softrock40/conversations/topics/49291
                  Original Message -----
                  From: "allgyer@... [softrock40]" <softrock40@yahoogroups.com>
                  To: <softrock40@yahoogroups.com>
                  Sent: Saturday, June 14, 2014 11:06 AM
                  Subject: Re: [softrock40] Ensemble RXTX Help


                  >I have to be missing something or misunderstanding Alan. If that is the case, how does the input ever develop +2.5V?
                  >
                  > Warren Allgyer
                  > 9V1TD
                • warrenallgyer
                  Alan The post you cited would not seem applicable to the measurements in this case. The diodes on the 6231 limit the differential between the + and - inputs to
                  Message 8 of 10 , Jun 14, 2014
                    Alan

                    The post you cited would not seem applicable to the measurements in this case.

                    The diodes on the 6231 limit the differential between the + and - inputs to 0.7 volts. The 6231 is referenced to the voltage divider which should produce 2.5 volts. Clamping diodes on the 6231 will limit the input on the - input to 0.7 volts referenced to the + input or a range of 1.8 to 3.2 volts. This does nothing to change the reference voltage itself because the clamping diodes are between the two inputs and not between the inputs and ground.

                    Warren Allgyer
                    9V1TD
                  • Alan
                    Original Message ----- Subject: Re: [softrock40] Ensemble RXTX Help Warren , ... Seems to confirm what I say beow?? Is it not the same fault ? I am not
                    Message 9 of 10 , Jun 14, 2014
                    Original Message -----
                    Subject: Re: [softrock40] Ensemble RXTX Help


                    Warren ,

                    > The post you cited would not seem applicable to the measurements in this case.

                    Seems to confirm what I say beow?? Is it not the same "fault"?

                    I am not pretending to know what happens. Just that it does.This has been observed before when some others have put all the ICs in
                    first. Diodes were a suggestion made by someone to explain why. Diodes are everywhere on the inputs including the transistor B-E..
                    If Pete does not confirm all is correct when he finishes then we'll start worrying.

                    73 Alan G4ZFQ

                    >
                    >
                    > The diodes on the 6231 limit the differential between the + and - inputs to 0.7 volts. The 6231 is referenced to the voltage
                    > divider which should produce 2.5 volts. Clamping diodes on the 6231 will limit the input on the - input to 0.7 volts referenced to
                    > the + input or a range of 1.8 to 3.2 volts. This does nothing to change the reference voltage itself because the clamping diodes
                    > are between the two inputs and not between the inputs and ground.
                    >
                    > Allgyer
                    > 9V1TD
                  • warrenallgyer
                    I am not disputing that it happens. I am disputing that the diodes are the cause. Those diodes are not going to cause the problem that he cites. Those diodes
                    Message 10 of 10 , Jun 14, 2014
                      I am not disputing that it happens. I am disputing that the diodes are the cause.

                      Those diodes are not going to cause the problem that he cites. Those diodes prevent either input from exceeding the power rail by more than 0.7 volts and prevent a differential input of more than 0.7 volts. They do not shunt the + input to ground which is what would be needed to pull his voltage divider down.

                      Warren Allgyer
                      9V1TD
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