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Re: Bad chip? Not that one, in any case.

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  • wfahle
    It indicates 5v on pin 1, Just like the other one in that respect. With power off, I m currently reading 20.9 Kohms between pin 1 and pin 8, which when
    Message 1 of 28 , Nov 3, 2012
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      It indicates 5v on pin 1, Just like the other one in that respect. With power off, I'm currently reading 20.9 Kohms between pin 1 and pin 8, which when reviewing the schematic doesn't seem right. In fact the other dual op-amp which seems wired similarly is an open circuit between those pins, giving me more confidence that this is the problem. I'm reading 11Kohms between 8 and 2 on U6, which is probably where the 20.9 is coming from adding R16 (which spans 1 and 2). Any ideas anyone? Clearly there is a short somewhere, and not a bad chip after all.

      --- In softrock40@yahoogroups.com, "MICHAEL TALLENT" <mwtallent@...> wrote:
      >
      > Noise probably will not matter for the transmitting side, the output level
      > may not be as good as amps designed for low voltage operation, but try it
      > and see.
      >
      > Mike T
      >
      > ----- Original Message -----
      > From: "wfahle" <billfahle@...>
      > To: <softrock40@yahoogroups.com>
      > Sent: Friday, November 02, 2012 12:46 PM
      > Subject: [softrock40] Re: Bad chip?
      >
      >
      > > Ok, I've recovered from the brain fart, and am back on track now. This
      > > OP-Amp (dual) is in the transmitter, as U6. Do you think noise will cause
      > > a problem? I think I will try it anyway this weekend, because I am
      > > installing it dead-bug style with individual wires to each lead, so it
      > > will be easily replaced. This will allow me to finish the transmitter and
      > > see what I get signal-report wise.
      > >
      > > --- In softrock40@yahoogroups.com, "MICHAEL TALLENT" <mwtallent@>
      > > wrote:
      > >>
      > >> You really want a low noise op-amp for this application as it will
      > >> determine
      > >> the noise floor of your receiver. The data sheet you linked looks like
      > >> nothing special, so you will not get the performance that these receivers
      > >> are capable of.
      > >>
      > >> Mike T W6MXV
      > >>
      > >> ----- Original Message -----
      > >> From: "wfahle" <billfahle@>
      > >> To: <softrock40@yahoogroups.com>
      > >> Sent: Wednesday, October 31, 2012 12:31 PM
      > >> Subject: [softrock40] Re: Bad chip?
      > >>
      > >>
      > >> > Well NOW it's the chip for sure. In an attempt to remove the IC to
      > >> > check
      > >> > voltages and such, the green covering began to burn through exposing
      > >> > the
      > >> > copper traces beneath. So I got out the clippers and clipped it loose
      > >> > from
      > >> > the board, so that I could remove each lead individually. This worked,
      > >> > but
      > >> > it tore up some of the pads in the process. I intend to replace it with
      > >> > this chip because it is available locally (and I don't think going SMT
      > >> > again is going to make life any easier):
      > >> > http://www.nteinc.com/specs/700to799/pdf/nte778a.pdf
      > >> >
      > >> > --- In softrock40@yahoogroups.com, "wfahle" <billfahle@> wrote:
      > >> >>
      > >> >> Ok, I pulled R16, and it still reads 5v at pin 1. R16 measures out at
      > >> >> 10k
      > >> >> as it should, but with it pulled there is very little voltage at pin
      > >> >> 2.
      > >> >> The current, since I can now measure it, across R16 is .24mA. The
      > >> >> votage
      > >> >> at pin 7 doesn't change either; it's still almost zero. The others
      > >> >> besides 2 are unchanged. Pin 2 goes almost to zero vs. the 2.5 it had
      > >> >> been reading. I guess R16 becomes part of a voltage divider under the
      > >> >> circumstances; I don't understand circuits this complex. So I will try
      > >> >> to
      > >> >> unseat U6 and see if there is a solder bridge under it from 1 to 8 or
      > >> >> something (they are across from each other).
      > >>
      >
    • Alan
      ... Subject: [softrock40] Re: Bad chip? Not that one, in any case. ... I do not remember you giving the voltages you see on this chip. 73 Alan G4ZFQ
      Message 2 of 28 , Nov 3, 2012
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        ----- Original Message -----
        Subject: [softrock40] Re: Bad chip? Not that one, in any case.


        > It indicates 5v on pin 1, Just like the other one in that respect. With power off, I'm currently reading 20.9 Kohms between pin 1
        > and pin 8, which when reviewing the schematic doesn't seem right. In fact the other dual op-amp which seems wired similarly is an
        > open circuit between those pins, giving me more confidence that this is the problem. I'm reading 11Kohms between 8 and 2 on U6,
        > which is probably where the 20.9 is coming from adding R16 (which spans 1 and 2). Any ideas anyone? Clearly there is a short
        > somewhere, and not a bad chip after all.
        >


        I do not remember you giving the voltages you see on this chip.

        73 Alan G4ZFQ
      • wfahle
        I am giving continuity checks now. I was reading 5v on pin 1, which was the original problem that made me suspect the chip was bad. In fact it looks like R15
        Message 3 of 28 , Nov 3, 2012
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          I am giving continuity checks now. I was reading 5v on pin 1, which was the original problem that made me suspect the chip was bad. In fact it looks like R15 is shorted to ground between it and C6+. That is not indicated in the schematic, so I'm now pulling R15.

          --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
          >
          >
          > ----- Original Message -----
          > Subject: [softrock40] Re: Bad chip? Not that one, in any case.
          >
          >
          > > It indicates 5v on pin 1, Just like the other one in that respect. With power off, I'm currently reading 20.9 Kohms between pin 1
          > > and pin 8, which when reviewing the schematic doesn't seem right. In fact the other dual op-amp which seems wired similarly is an
          > > open circuit between those pins, giving me more confidence that this is the problem. I'm reading 11Kohms between 8 and 2 on U6,
          > > which is probably where the 20.9 is coming from adding R16 (which spans 1 and 2). Any ideas anyone? Clearly there is a short
          > > somewhere, and not a bad chip after all.
          > >
          >
          >
          > I do not remember you giving the voltages you see on this chip.
          >
          > 73 Alan G4ZFQ
          >
        • wfahle
          Found the problem. See other thread.
          Message 4 of 28 , Nov 3, 2012
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            Found the problem. See other thread.

            --- In softrock40@yahoogroups.com, "wfahle" <billfahle@...> wrote:
            >
            > I am giving continuity checks now. I was reading 5v on pin 1, which was the original problem that made me suspect the chip was bad. In fact it looks like R15 is shorted to ground between it and C6+. That is not indicated in the schematic, so I'm now pulling R15.
            >
            > --- In softrock40@yahoogroups.com, "Alan" <alan4alan@> wrote:
            > >
            > >
            > > ----- Original Message -----
            > > Subject: [softrock40] Re: Bad chip? Not that one, in any case.
            > >
            > >
            > > > It indicates 5v on pin 1, Just like the other one in that respect. With power off, I'm currently reading 20.9 Kohms between pin 1
            > > > and pin 8, which when reviewing the schematic doesn't seem right. In fact the other dual op-amp which seems wired similarly is an
            > > > open circuit between those pins, giving me more confidence that this is the problem. I'm reading 11Kohms between 8 and 2 on U6,
            > > > which is probably where the 20.9 is coming from adding R16 (which spans 1 and 2). Any ideas anyone? Clearly there is a short
            > > > somewhere, and not a bad chip after all.
            > > >
            > >
            > >
            > > I do not remember you giving the voltages you see on this chip.
            > >
            > > 73 Alan G4ZFQ
            > >
            >
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