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Re: Ensemble RXTX build help

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  • g8voip
    Hi James, Just had to have one last check after finishing off todays batch of email questions and turning off the PC Oh ye of little faith! As I repeatedly
    Message 1 of 20 , Mar 27, 2011
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      Hi James,

      Just had to have one last check after finishing off todays batch of email questions and turning off the PC

      Oh ye of little faith!

      As I repeatedly say, it is extremely rare to have a brand new component that is faulty. Yes it does happen, but 99.9% of the time its not the component, something else.

      Should hopefully be straight forward to find where the short from pin 1 to ground is and solve the problem.

      Definitely off to hit the sack now!

      73, Bob G8VOI

      --- In softrock40@yahoogroups.com, "James" <ki7el@...> wrote:
      >
      > Hi Bob:
      >
      > You are a genius.
      >
      > I soldered R11 to pin one, took the bits to the work bench, turned
      > my bench supply down to 5vdc, hooked it all up and when power is applied I get 290 ohms across pins 3 and 4, infinite ohms when no power is applied.
      >
      > The opto-isolator lives!
      >
      >
      > --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@> wrote:
      > >
      > >
      > > Hi James,
      > >
      > > When trying to measure the diode (LED) in the opto isolator the forward volt drop is higher than a conventional diode, so it could be that the terminal voltage of your meter is not high enough to cause the LED to conduct, hence it appears to be open circuit both ways. Some DVM's have one specific range for measuring semiconductors.
      > >
      > > As you have cut and isolated pin 1 of the opto, I would suggest monitoring pin 4 with your meter and connect the remains of pin 1 to 5V via 470 ohm resistor to see if the opto actually does turn on ok, i.e. pin 4 goes to 0V.
      > >
      > > I have just taken a look at the ExpressPCB artwork, and although possibly not the latest version, I suspect the layout is still the same. There is only the short track on the top surface from R11 to pin 1, so I cannot see anywhere that would short to 0V, so the problem is most likely on the bottom side and possibly a whisker to the surrounding 0V earth plane.
      > >
      > > Try cleaning up the pad with IPA or similar cleaner and take a look with an eye glass, you might be able to see something. Use a sharp knife or scapel to carefully cut around the pad on pin 1 and keep on checking if the short has been cleared. The other choice when you have the opto removed is to simple use a drill to clear the pad away and solder pin one on the top surface to link to R11.
      > >
      > > With the opto removed, pin 1 should be isolated from 0V, so it should not be too difficult to locate the problem. The PCB only has the 2 layers so no need to worry about shorts on the plated through hole to an inner layer ground plane etc. Should be no reason to have to bend pin 1 out when you fit the replacement opto.
      > >
      > > Before you remove the opto however, I would clean off the solder from the pin 1 pad, take a good look and try to clear any possibly debris or spurious whisker of track to the ground plane. If you can clear it, and have checked the opto is working as suggested, might be able to simply rejoin pin 1 and continue.
      > >
      > > 73, Bob G8VOI
      > >
      > >
      > >
      > >
      > > --- In softrock40@yahoogroups.com, "James" <ki7el@> wrote:
      > > >
      > > > Hi Bob:
      > > >
      > > > Your advice was excellent.
      > > >
      > > > I couldn't get the opto-isolator out with the tools I have so I clipped pin 1 knowing that I could always carefully solder a jumper to bring it back to life. Also R11 is out of the circuit for this test. I can always solder it back in.
      > > >
      > > > At any rate I tested the LED of the opto-isolator and it's open both directions. I used my ohm meter knowing that current can only flow one way in a diode (LED), it's dead, it shows open both directions.
      > > >
      > > > I cleaned up the board a bit and tested R11 where it meets pin 1 of the opto-isolator to see if it was shorted to ground, it is. Of course this means pin 1 of the opto-isolator is also shorted to ground but I tested that too just to be sure, it is.
      > > >
      > > > I'll purchase a new 859-LTV-817A from Mouser. Hell at 20 cents each I might as well buy enough to justify the shipping.
      > > >
      > > > To get around the short I plan to solder the end of R11 that mates with pin 3 of the ATTiny85 to the board as usual. I'll bend pin one of the replacement opto-isolator up and solder the remaining three pins to the board as usual. I'll then solder the other end of R11 directly to pin 1 of the opto-isolator. Problem solved.
      > > >
      > > > Your thoughts?
      > > >
      > > >
      > > > --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@> wrote:
      > > > >
      > > > > Hi James,
      > > > >
      > > > > If you can remove the opto in one piece, it is worth checking that there is not a small whisker or un-etched piece of copper track creating the short. You can check both the PCB and opto separately.
      > > > >
      > > > > It is very unusual to have that sort of failure in a new component, but on a few isolated occassions there have been instances of minor problems in the PCB production process reported.
      > > > >
      > > > > 73, Bob G8VOI
      > > > >
      > > > >
      > > > >
      > > > > --- In softrock40@yahoogroups.com, "James" <ki7el@> wrote:
      > > > > >
      > > > > > Hi Alan:
      > > > > >
      > > > > > You're correct of course. Yes, pin four is ground, Pin three is positive voltage out.
      > > > > >
      > > > > > When in receive mode I have no voltage across those two pins. When in transmit mode I have 4.7vdc across those pins.
      > > > > >
      > > > > > At least I knew the ATTiny85 was working properly. Too bad my opto-isolator isn't. :)
      > > > > >
      > > > > >
      > > > > > --- In softrock40@yahoogroups.com, "Alan" <alan4alan@> wrote:
      > > > > > >
      > > > > > >
      > > > > > > ----- Original Message -----
      > > > > > > Subject: [softrock40] Re: Ensemble RXTX build help
      > > > > > >
      > > > > > >
      > > > > > > > After many hours of testing I've discovered that Rocky is switching
      > > > > > > > power on on pins 3 and 4 of the ATTiny85 chip when the Tx button in Rocky
      > > > > > > > is pressed.
      > > > > > > >
      > > > > > > > It's late so I won't test the output of the opto-isolator until tomorrow.
      > > > > > > >
      > > > > > > James,
      > > > > > >
      > > > > > > Maybe it's because it is late for you.
      > > > > > > Pin 3 should switch. Pin 4 should be ground and not switch.
      > > > > > > Early for me, just lost an hour here in the Summertime change.
      > > > > > >
      > > > > > > 73 Alan G4ZFQ
      > > > > > >
      > > > > >
      > > > >
      > > >
      > >
      >
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