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Re: [softrock40] SDR40 v6.1 TX/RX stopped working

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  • Tony Parks
    Hi Ian, Sure looks like U8 is a problem. Let me know what components you need to restore your board and I will send them right away at no cost. 73, Tony
    Message 1 of 47 , Aug 2 2:44 AM
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      Hi Ian,
       
      Sure looks like U8 is a problem.  Let me know what components you need to restore your board and I will send them right away at no cost.
       
      73,
      Tony KB9YIG
       
      Hi Tony, I searched for and found my digital thermometer and took readings on the unit as follows:
      U1 69.4 F
      U2 69.2 F
      U3 72.6 F
      U4 95 F
      U5 77 F
      U6 74.6 F
      U7 79.3 F
      U8 86 F
      U8 pin 7 reads 4.2V
       
      Ian
    • Len Warner
      ... Perhaps, but output near the +ve rail could be: a) inputs driven to output saturation b) output pulled high externally (i.e. by a pins 7-8 short) c) device
      Message 47 of 47 , Aug 3 11:49 PM
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        >U8 86 F
        >U8 pin 7 reads 4.2V
        >
        >Ian
        At 2:44 am ((PDT)) Thu Aug 2, 2007, in Digest 1865 Tony Parks wrote:

        >Sure looks like U8 is a problem.

        Perhaps, but output near the +ve rail could be:
        a) inputs driven to output saturation
        b) output pulled high externally (i.e. by a pins 7-8 short)
        c) device failure which also emulates (a) or (b).

        Both (b) and (c) can explain the U8 heating
        but only (c) is that device's fault.
        (There's no source for the heating current in case (a).)

        Meanwhile, none of these explain why:
        d) Q9 ran hot and
        e) Q9 replacement ran hot
        This doesn't seem to be in a related part of the circuit,
        so was Ian just unlucky with two rogue 2N3904?

        [BTW, my apologies for saying that Q9 collector pad voltage
        3.63V with Q9 removed seemed too low. I recalculated as
        3.64V - within the DVM last digit uncertainty.
        (Vcc-Q8vbe) * R40/(R35+R40) + Q8vbe =
        (4.32-0.65) * 22.1/(4.99+22.1) + 0.65 = 3.64V ]

        >Let me know what components you need to restore your board
        >and I will send them right away at no cost.

        I continue to admire your outstanding support for this project;
        "May Great Leader Tony live ten thousand years!"


        Regards, LenW
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