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Re: Switched BPF problems

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  • g8voip
    Hi Rob, Good to hear that. I would never have seen anything like that as I just build the thing up completely from the circuit diagram and layout, then test it
    Message 1 of 5 , Mar 27, 2009
      Hi Rob,

      Good to hear that.

      I would never have seen anything like that as I just build the thing up completely from the circuit diagram and layout, then test it afterwards and watch for smoke!

      When I looked at that procedure after I saw your message, that was the first thing that to sprang to mind. You get some very strange effects when pins are open circuit and floating, all sorts of capacitive charging effects etc.

      Now if you had been using a good old 'AVO' meter, that would not have occurred!

      Hope you finish it soon and have fun!

      73, Bob G8VOI

      --- In softrock40@yahoogroups.com, "g4rqj" <robandaud@...> wrote:
      >
      >
      > Hi Bob
      > Spot on, 10k across the meter and all readings now correct.Suspected something like that as the inputs/outputs are just floating.I'll drop a note to WB5RVZ (the proceedure writer ) if he doesn't pick it up from here. Thanks again,
      > Rob
      > G4RQJ/G8AOR
      > --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@> wrote:
      > >
      > > Hi Rob,
      > >
      > > I doubt very much if you have damaged the devices. Check to make sure that there are no obvious solder splashes etc.
      > >
      > > I have just taken a look at that test procedure for the first time ever. I do not know what you would expect to see on those pins as they are just floating inputs or output, effectively open circuit, so I would imagine they could easily float to anything.
      > >
      > > Using a DVM to measure, being very high impedance there is no path to 'discharge' the pins (bad term I know). I would try putting a resistor between the pin and ground when you make the measurement, say 10k, and see what the voltage measured is then.
      > >
      > > Not really too sure what the validity of testing the pins not being used is apart from seeing perhaps if they are shorted to an adjacent one, which a visual inspection would do.
      > >
      > > I doubt if there is really a problem,
      > >
      > > 73, Bob G8VOI
      > >
      > > --- In softrock40@yahoogroups.com, "petergouweleeuw" <peter@> wrote:
      > > >
      > > > Rob,
      > > > I finished mine just a week ago.
      > > > All my step by step testing and measurements were within a few milliVolt. have a carefull look to your soldering again. You also might try to see if all trails on the board are okay.
      > > >
      > > > Good luck.
      > > > Peter PA2V
      > > >
      > > > --- In softrock40@yahoogroups.com, "g4rqj" <robandaud@> wrote:
      > > > >
      > > > > Wonder if anyone else has had similar problems. Assembling using the step by step instructions and attempting the switching test with no filters fitted, 2.48V steps through both switches in sympathy with the JP1JP2 settings BUT the other test points are not all below 1V,in fact some can be as high as 3.2V. Have I really killed both FT3253's? I did take the usual ESD precautions which I am used to having done bench work for 50 odd years or are these points floating in the absence of any output connections? The two control lines reach the ic's successfully, pins 7 and 9 are set correctly at 2.48V. Pins 1 and 15 are grounded Any suggestions appreciated
      > > > > PS is there a uk source of FST3253?
      > > > > Rob
      > > > > G4RQJ
      > > > >
      > > >
      > >
      >
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