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13411Re: SDR40 v6.1 TX/RX stopped working

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  • Len Warner
    Aug 2, 2007
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      At 6:54 am ((PDT)) Wed Aug 1, 2007, ian mcphedran wrote:

      >I have removed Q9 again.
      >The 5V line is 4.32V, U4 is running hot, and the input current at 12.5V is
      > Q9 collector pad reads 3.63V, base pad reads 0V as of course does the
      > emitter.

      3.63V is too low for the potential divider U4, R35, R40, Q8 base,
      so the Q9 collector node is definitely connected to something
      else - I wouldn't have expected the /OE inputs of Q3
      to represent a significant load, they are CMOS inputs
      and hence high-impedance, aren't they?

      When Q9 was hot, something was sourcing current to it:
      now it's gone, something is sinking a little current from the
      collector node but the high current is still flowing from U4.

      The only other stray thought I have is that you are testing
      in the aluminium box, the box is not isolated from supply,
      and there is a short. Unlikely, but...

      Regards, LenW
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