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69613Re: Bad chip?

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  • wfahle
    Oct 30, 2012
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      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).

      --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
      >
      >
      > ----- Original Message -----
      > Subject: [softrock40] Re: Bad chip?
      >
      >
      > > On R50 Hairpin (the standard regular ground reference from the power supply stage).
      > >
      >
      > Right, maybe the voltage is coming through the mixer with some sort of diode action.
      >
      >
      > >> > Everything checks out fine except for 2 voltages. Pin 1 of U6 is reading 5 volts instead of 2.5,
      >
      > This could be the IC, but look for a possible PCB fault, a whisker shorting to 5V.
      > But presumably pins 2,3 are 2V5? Why is 5V not sent to pin 2 via R16? Check R16 and soldering.
      >
      > 73 Alan G4ZFQ
      >
      >
      >
      > and pin 7 of that same chip is
      > >> > reading near 0, instead of 2.5. This is unbridged, with or without the USB connected, with power.
      > >> >
      > >> > It has passed all prior tests, including receiving a signal in CW over the air. I have continuity-tested every pin of both
      > >> > chips
      > >> > U6 and U7 to make sure each pin connects to each solder joint, and I have checked that no pin shorts to any other pin, except
      > >> > pin
      > >> > 3 to pin 5 on both chips, as they should. Pin 1 to Pin 6 shows 10k resistance, as it should, on both chips. I have
      > >> > double-checked
      > >> > the value of every resistor in the TX circuit. I even pulled R21 to do a direct measure because it was reading about half its
      > >> > actual value plugged in. Pulled it read 2.21k as expected. Pin 1 and 7 of U7 both read correct values of 2.5 volts. So my
      > >> > question
      > >> > is, do I have a bad chip? Something else I can check?
      > >> >
      > >> > The voltage to R23 hairpin is 2.5, as is R15 and R16, R24, R22, R21, R20, R19 and R18. Only R17 reads 5 volts. I can't see how
      > >> > it
      > >> > is coming anywhere but from the chip.
      > >> >
      > >> > R25 is -1.2, R26 is 2.5, R27 is 2.5, and R28 is 1.6. The weirdest one there is R25, so I checked the other side of it and it
      > >> > reads -.9. The last chip is uninstalled at this point, but I'm not sure where the negative voltage is coming from.
      > >> >
      > >> >
      > >>
      > >> Where have you got the meter negative clip?
      > >>
      > >> 73 Alan G4ZFQ
      > >>
      > >
      > >
      > >
      > >
      > > ------------------------------------
      > >
      > > Yahoo! Groups Links
      > >
      > >
      > >
      >
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