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RXTX Ensemble, lots of headaches / faulty board

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  • jess_flyin_high
    I built the entire softrock before testing anything (I have years of smd work under my belt so I was sure of my soldering skills) when I powered it up for the
    Message 1 of 32 , Nov 1, 2012
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      I built the entire softrock before testing anything (I have years of smd work under my belt so I was sure of my soldering skills)

      when I powered it up for the first time I was met with a very hot 5v regulator and ac74 (>200ma draw on 12v line)

      I checked and triple checked the soldering on the ac74 with no faults found, so assuming a faulty chip I ordered 2 new ones.

      while waiting for delivery of the new chips I turned the multipliers off on the si570 and linked the clock input for the ac74 through to pin 9 (one of the qsd lines) for the ac74, this allowed me to use the ensemble in RX only (with no image rejection).

      When the new chips arrived I checked that everything was as it should be where the ac74 mounts and found that the 2 qsd lines were shorted, followed it through to the rx mixer and sure enough pin 2 was shorted to pin 14 (there was no way that this was down to bad soldering, adjacent pins maybe but not when they are on opposite sides of the chip) I assumed the fs3253 was faulty and removed it from the board only to find that pis 2 and 14 were still shorted on the board with the chips removed.

      close examination of the tracks in question revealed no visible fault, so I resorted to track cutting, after cutting the 2 tracks just to the left of where they pass under R25 removed the short from the ac74 end, cutting the tracks to the right of R28 removed the short from the fst3253 end.

      after all the messing around I can say for certain that the tracks that pass under R25 - R28 are shorted together within the board (area shown in pc at http://81.168.22.130/shorted.jpg)

      does anyone know of a cheap supplier of the fst3253 chip in the uk since mine did not survive removal from the board?
    • Chris Stake
      Ok, at least it proves I was paying attention. :-) Chris From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On Behalf Of jess_flyin_high
      Message 32 of 32 , Nov 3, 2012
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        Ok, at least it proves I was paying attention. :-)

         

        Chris

         

         

         

        From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On Behalf Of jess_flyin_high
        Sent: 03 November 2012 03:38
        To: softrock40@yahoogroups.com
        Subject: [softrock40] Re: RXTX Ensemble, lots of headaches / faulty board

         

         

        The whisker you can see in the pic is a result of me leaning over the board to take the picture a couple of hours after having my hair cut

        Jess

        --- In softrock40@yahoogroups.com, "Chris Stake" <stake@...> wrote:
        >
        > What's that filament on the PCB which encircles the legend for R28 on your
        > picture? Could it be a whisker of wire? Is that the culprit?
        >
        > Chris

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