Avionics-List Digest Archive

Tue 04/21/09


Total Messages Posted: 3



Today's Message Index:
----------------------
 
     1. 08:18 AM - 757 mic bias voltage (Greg Young)
     2. 09:33 AM - Re: Side tone (Doug McNutt)
     3. 10:29 AM - Avionics cooling fans - yea or nay?? (McFarland, Randy)
 
 
 


Message 1


  • INDEX
  • Back to Main INDEX
  • NEXT
  • Skip to NEXT Message
  • LIST
  • Reply to LIST Regarding this Message
  • SENDER
  • Reply to SENDER Regarding this Message
    Time: 08:18:49 AM PST US
    From: "Greg Young" <gyoung@cs-sol.com>
    Subject: 757 mic bias voltage
    I've got a friend that flys 757's using a Bose headset and has the mic get hot (warm) during the course of a flight, not burn-your-lips-hot, but too hot. Talked to the Bose service mgr here at Sun n Fun and he wants to know what the mic bias voltage is since a replacement mic didn't fix it. FWIW, the mic is live continuously because of the CVR. I thought there might be someone in the brain trust here that might know the answer or have any other ideas. It's not a problem in GA aircraft - he flew with me to SnF in my Navion for 5 hrs and had no problem. Likewise none in his GA airplanes. Regards, Greg Young


    Message 2


  • INDEX
  • Back to Main INDEX
  • PREVIOUS
  • Skip to PREVIOUS Message
  • NEXT
  • Skip to NEXT Message
  • LIST
  • Reply to LIST Regarding this Message
  • SENDER
  • Reply to SENDER Regarding this Message
    Time: 09:33:55 AM PST US
    From: Doug McNutt <douglist@macnauchtan.com>
    Subject: Re: Side tone
    At 10:32 -0600 4/19/09, I wrote: >It's been almost two decades since I have had a Sigtronics apart and I never owned one. I'll have a look at my records later today. There might be a schematic around. I found a schematic. The SPA-400 uses diode isolation to activate the transmitter key. Activation of the transmitter without going through SPA-400 pins 2 (pilot) or 10 (copilot) will not be recognized by the intercom. The intercom normally removes power from its headphone amplifier when either the copilot or pilot push-to-talk key is pressed and diodes see that the aircraft's push-to-talk system is also activated. The output of the audio amplifier goes through 1 1 microfarad capacitor and a 100 ohm resistor to the aircraft's headphone bus, The 100 ohms allows for the audio from other sources - like a radio or audio panel - to be connected to the same bus where the audio signals are mixed. A part of the on-off switch connects the aircraft microphone bus to the SPA-400 when it is turned on but reconnects mic bus directly to the pilot microphone when off. I'm now betting that the Gordon's problem has to do with his microphone jack being wired so that he grounds the aircraft push-to-talk wire directly instead of going through pin 2 of the intercom connector. If I'm wrong there is a diode failure inside of the intercom, probably CR-7. Off line at dmcnutt@macnauchtan.com if you want to talk in more detail about the schematics. I'm not sure about copyright and non-disclosure issues. -- --> Life begins at ovulation. Ladies should endeavor to get every young life fertilized. <--


    Message 3


  • INDEX
  • Back to Main INDEX
  • PREVIOUS
  • Skip to PREVIOUS Message
  • NEXT
  • Skip to NEXT Message
  • LIST
  • Reply to LIST Regarding this Message
  • SENDER
  • Reply to SENDER Regarding this Message
    Time: 10:29:02 AM PST US
    Subject: Avionics cooling fans - yea or nay??
    From: "McFarland, Randy" <Randy.McFarland@novellus.com>
    I have a Garmin 327 transponder and Dynon D-10 that I suspect become unreliable and freeze or lock up due to high behind the panel temperatures. Have any of the group experienced avionics issues related to heat, and will/does cooling fans provide enough cooling to eliminate the problems? Randy




    Other Matronics Email List Services

  • Post A New Message
  •   avionics-list@matronics.com
  • UN/SUBSCRIBE
  •   http://www.matronics.com/subscription
  • List FAQ
  •   http://www.matronics.com/FAQ/Avionics-List.htm
  • Web Forum Interface To Lists
  •   http://forums.matronics.com
  • Matronics List Wiki
  •   http://wiki.matronics.com
  • 7-Day List Browse
  •   http://www.matronics.com/browse/avionics-list
  • Browse Avionics-List Digests
  •   http://www.matronics.com/digest/avionics-list
  • Browse Other Lists
  •   http://www.matronics.com/browse
  • Live Online Chat!
  •   http://www.matronics.com/chat
  • Archive Downloading
  •   http://www.matronics.com/archives
  • Photo Share
  •   http://www.matronics.com/photoshare
  • Other Email Lists
  •   http://www.matronics.com/emaillists
  • Contributions
  •   http://www.matronics.com/contribution

    These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.

    -- Please support this service by making your Contribution today! --