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69688RE: [softrock40] Re: RXTX Ensemble, lots of headaches / faulty board

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  • Chris Stake
    Nov 2, 2012
    • 0 Attachment

      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

       

      From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On Behalf Of Brent G DeWitt
      Sent: 02 November 2012 00:27
      To: softrock40@yahoogroups.com
      Subject: RE: [softrock40] Re: RXTX Ensemble, lots of headaches / faulty board

       

       

      The silkscreen might hide an etch short, but it is totally non-conductive.

      Brent, AB1LF
      Milford, MA

      > -----Original Message-----
      > From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On
      > Behalf Of Chris Wilson
      > Sent: Thursday, November 01, 2012 7:50 PM
      > To: softrock40@yahoogroups.com
      > Subject: Re: [softrock40] Re: RXTX Ensemble, lots of headaches / faulty
      > board
      >
      >
      >
      > >
      > > still cant see any sign of where the short is (the tracks look
      > perfect
      > > as you can see in the picture I linked to).
      >
      > > The shorted section is removed from the circuit by track cuts and has
      > > been replaced with link wires so in theory once I have a replacement
      > > chip it should be fully working
      >
      > > Jess
      > > 2E0VBR
      >
      > > --- In softrock40@yahoogroups.com, John Greusel <greusel@...> wrote:
      > >>
      > >> Jess,
      > >> That was very good sleuthing- interesting problem too.
      > >> Hopefully we won't see that happen again. I suspect someone will
      > help you with that chip in the UK.
      > >> Could you actually see where the short was?
      > >>
      > >> John
      > >> KC9OJV
      > >>
      > >>
      > >>
      > >> Â
      > >>
      > >>
      > >>
      > >> ________________________________
      > >> From: jess_flyin_high <jess@...>
      > >> To: softrock40@yahoogroups.com
      > >> Sent: Thursday, November 1, 2012 3:01 PM
      > >> Subject: [softrock40] RXTX Ensemble, lots of headaches / faulty
      > board
      > >>
      > >>
      > >> Â
      > >> 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?
      > >>
      >
      > >
      >
      >
      > 01/11/2012 23:46
      >
      > Pardon me if this is totally foolish and naive, but is there any way
      > the screen print showing the orientation of R25, R26, R27 and R28,
      > passing over both tracks, could conduct, or be hiding the defect? It
      > may be coincidental four straight lines of screen print cross these
      > tracks, but it did strike me as worthy of comment. Great detective work
      > by the builder, he should change his forum name to Sherlock :)
      >
      > --
      > Best Regards,
      > Chris Wilson. 2E0ILY
      >
      >
      >
      > ------------------------------------
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