Mazurb Posted September 29, 2014 Share Posted September 29, 2014 We have a 74 year C-130H1 with a #2 VHF radio that wil not turn off through SCNS. Turning off SCNS also does not shut off the radio. We have swapped IDCUs, RTs and mounts, and have checked the Power on/off signal wire for continutity and a short to ground. Everything checks out. Also, Bypassing Secure voice has no effect. Has anyone seen this before or have any out of the box ideas? We've got a head scratcher here. Quote Link to comment Share on other sites More sharing options...
munirabbasi Posted October 1, 2014 Share Posted October 1, 2014 Mazurb Hi Your problem look like SCNS control unit plug wiring defective , see wiring Munir Abbasi Home of hercules pakistan Quote Link to comment Share on other sites More sharing options...
tinyclark Posted October 2, 2014 Share Posted October 2, 2014 Pull the wire out of pin U on J2 at the R/T. If it still comes on, I would be very puzzled. There is only one wire between the C/P's IDCU and the R/T.VHF #2 wiring.pdf Quote Link to comment Share on other sites More sharing options...
Mazurb Posted September 16, 2015 Author Share Posted September 16, 2015 So I finally was able to re-attack this problem. We have pulled pin 54 from the plug at the Co's IDCU and pin U at the radio. both times the radio still turned on, and we could not shut if off! We have verified no shorts to ground at pin 54 and U to all other wires in the IDCU connector. We have changed out the Co's IDCU and pulled the breakers on the other two IDCU's. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted September 17, 2015 Share Posted September 17, 2015 (edited) Are there other pins next to pin U that are sources of ground? Maybe there is a pin locking tab from another pin touching pin U. Edited September 18, 2015 by tinyclark Quote Link to comment Share on other sites More sharing options...
tinyclark Posted September 22, 2015 Share Posted September 22, 2015 We know two things. There is 28 VDC going to the radio, and the radio is turning on via a ground from somewhere. I don't have the connector layout for J2, but is Pin A anywhere near pin U? Here's what I would do if I was working on the aircraft. Remove the ground terminal lug from the aircraft frame going to pin A on J2. I would think that if you removed the power and chassis grounds lugs going to the chassis and power grounds of J1, pins P & E, that the radio would be dead. Having said all of this, it may be worth getting a new plug for J2, and pulling all wires out of the old plug, verifying wire numbers, and repinning into the new connector. Good luck. VHF #2 wiring.pdf Quote Link to comment Share on other sites More sharing options...
Mazurb Posted February 22, 2016 Author Share Posted February 22, 2016 Finally fixed it! It was a well hidden problem that existed ever since the plane was modified for ARC-186. (Reference 1C-130H-2-13 figure 4-6 2RF4.00) The wire RF2018C20 was supposed to have been removed from pin18 at the back of the adapter mount P1 and be spliced into RF2036A20. Both wires are 28VDC from the circuit breaker. Also pin 18 of the adapter mount J1 is connected to P2 pin H at the RT (not shown in the diagram). Pin H is the 24 VDC switched power developed internally. So when SCNS turned the radio on everything came alive. But when SCNS tried to power off, the 28 VDC at pin 18 provided by RF2018C20 was back feeding through the mount and J2 pin H the keeping the radio active even though the power on signal was not present at Pin U. So a missed step in a mod back in 1981~1985ish and missing info on a diagram lead to one hell of a wild goose chase. ARC186 VHF-FM.pdf Quote Link to comment Share on other sites More sharing options...
casey Posted February 22, 2016 Share Posted February 22, 2016 Nice find. One of those that you never forget... Quote Link to comment Share on other sites More sharing options...
tinyclark Posted February 24, 2016 Share Posted February 24, 2016 Way to go. Funny no one did a proper Op Ck after the mod. Of course, everyone assumes that once the SCNS is shut down. everything turns off. I don't know who initially caught that problem, but it was probably a fluke. Quote Link to comment Share on other sites More sharing options...
Mazurb Posted February 24, 2016 Author Share Posted February 24, 2016 It was me, we were trying to use it as an AM/FM radio when we first got the planes, before we really understood how these were wired. I had ATIS tuned in and still heard it when I turned it off. Weakly of course because we were pulling it in from just the coax connector on the front of the R/T. Quote Link to comment Share on other sites More sharing options...
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