Lucky13 Posted September 27, 2010 Share Posted September 27, 2010 We have a interphone problem that's been kicking our ass trying to track down so I figured I'd post here and see if anyone has any ideas we haven't tried. The Issue... We have a C-130 H2, Tail 87-9281 with a loud buzzing tone that is heard only in the Pilots, Copilots and Flight Intstructors stations. All other stations sound clear. The tone is heard regardless of which radios/nav systems are selected on the control box and volume panels. The tone in the bad stations goes away only when you press that call button, and only on the station which the call button is pressed. Troubleshooting... We have already pulled and swapped all the boxes and comm cords, doesn't look like an interphone control box or volume box. The tone is still heard even with one known good box plugged into the pilots station, all other stations unplugged. We suspected a bad ground so we checked the grounds and audio commons to every station and they checked fine. We also ohmed out the audio lines and didnt' find any shorts. We suspect noise coming from another system so we pulled every single circuit breaker to see if one made the noise stop, nothing made it go away. We pulled wires from every terminal on the interphone junction box one banded group at a time. No Effect. We suspected noise coming from the TRs so we pulled the breakers for them and ran off battery power. As long as AC power is applied ot the plane the noise persists. The ONLY thing other than the call button that makes the noise go away is running the interphone off battery power with no AC power applied to the plane. ??????? We are running out of ideas. Can anyone here think of anything? Quote Link to comment Share on other sites More sharing options...
tinyclark Posted September 27, 2010 Share Posted September 27, 2010 It may help to know what year and model of C130 you have. If I am going to guess, I'd like it to be an educated one. :-) Quote Link to comment Share on other sites More sharing options...
Lucky13 Posted September 27, 2010 Author Share Posted September 27, 2010 It may help to know what year and model of C130 you have. If I am going to guess, I'd like it to be an educated one. :-) 87 year, C130 H model... Quote Link to comment Share on other sites More sharing options...
Plaprad Posted September 28, 2010 Share Posted September 28, 2010 We had a Wombat with a similar problem, the refuel lights would not turn off, even with breakers pulled. Someone used bad wiring on the FE's interphone box and the lights were picking up power from the wires. Maybe there's some bad wires around where all three boxes head back to the rest of the system that is causing it. When you transmit, it's enough power to override the bleed through. Not sure where it could be, but that's my best guess. I'll talk to my buddy tonight, he's a Comm Nav guru. Quote Link to comment Share on other sites More sharing options...
RZHill Posted September 28, 2010 Share Posted September 28, 2010 What tail # Please Quote Link to comment Share on other sites More sharing options...
Plaprad Posted September 28, 2010 Share Posted September 28, 2010 My buddy said check the amplifier and change out with known good comm cords. The only thing he can think of other than those are bad wires somewhere. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted September 28, 2010 Share Posted September 28, 2010 (edited) I would order all three F11 filters for the 28VDC inputs. There are plenty in DLA. 5915-00-828-8336 Have you tried checking the grounding points on those filters? Also, insure the wire from terminal 23 has a good clean ground. You could also check the ground between the J-box and aircraft frame. I don't believe there was ever a strap installed between the J-box and aircraft, and i see nothing on the drawing. I think they just depended on the mounting hardware. Nothing wrong with hooking up a 16 guage wire between them. Edited September 28, 2010 by tinyclark Quote Link to comment Share on other sites More sharing options...
AMPTestFE Posted September 28, 2010 Share Posted September 28, 2010 AMP it, that'll fix her! Quote Link to comment Share on other sites More sharing options...
Lucky13 Posted September 28, 2010 Author Share Posted September 28, 2010 What tail # Please 87-9281 Quote Link to comment Share on other sites More sharing options...
tinyclark Posted September 28, 2010 Share Posted September 28, 2010 According to the H-2-13, that's an AIC-18, and I know the books are never wrong. Check the AC voltage on pin W (28VDC input) of one of those ICS boxes. It shouldn't be more than a volt. If it is, either those filters are not grounded, are bad, or there are 115AC bus power cables running next to the interphone wiring. Any recent mod work done on that bird? Quote Link to comment Share on other sites More sharing options...
Lucky13 Posted September 28, 2010 Author Share Posted September 28, 2010 According to the H-2-13, that's an AIC-18, and I know the books are never wrong. Check the AC voltage on pin W (28VDC input) of one of those ICS boxes. It shouldn't be more than a volt. If it is, either those filters are not grounded, are bad, or there are 115AC bus power cables running next to the interphone wiring. Any recent mod work done on that bird? We had a discussion about the 18 vs 25 isssue as well. The wiring diagram that matches the tail number and fits the wires on the plane is labeled AIC-18, however all the interphone boxes say AIC-25 on the back. Maybe the old 18 boxes are compatible with the wiring for the 25s so they just changed the boxes? We were planning to take a look at how noisy the DC current powering the boxes was but we got kicked off for an engine run, maybe tmw... Quote Link to comment Share on other sites More sharing options...
Predator25 Posted October 1, 2010 Share Posted October 1, 2010 The planes 81, 83, 85, and 87 have had AIC-25 boxes in them when we worked them here in Minneapolis, and I believe they even had those boxes when I was working on them in Milwaukee. (I was a traditional reservist in Milwaukee so I'm not positive about that time frame). I don't recall 81,83,85, or 87 having any weird interphone problems. Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted October 1, 2010 Share Posted October 1, 2010 Navy and Marine also have AIC-25 but we have AIC-18 info in the books as well. I think the change was with our "R" models (mid 70's) to 18 and then the "T" model (80's) has the 25. Same system (basic wiring) just different names? More capability (More radios, more wires, different boxes) on the later model so that might be it. Start the APU and use only the ESS AC bus to see if your issue is with the MAIN or LH/RH AC bus. If it is not the ESS (if you have the AC bus tie) tie the main AC bus and see if the issue is there or in the LH/RH AC bus... Quote Link to comment Share on other sites More sharing options...
CharlieLifeSupport Posted October 2, 2010 Share Posted October 2, 2010 Are the headsets plugged into the comm. cords on the quick-don O2 masks? Those cords are not very sturdy. Quote Link to comment Share on other sites More sharing options...
Lucky13 Posted October 13, 2010 Author Share Posted October 13, 2010 Navy and Marine also have AIC-25 but we have AIC-18 info in the books as well. I think the change was with our "R" models (mid 70's) to 18 and then the "T" model (80's) has the 25. Same system (basic wiring) just different names? More capability (More radios, more wires, different boxes) on the later model so that might be it. Start the APU and use only the ESS AC bus to see if your issue is with the MAIN or LH/RH AC bus. If it is not the ESS (if you have the AC bus tie) tie the main AC bus and see if the issue is there or in the LH/RH AC bus... We did exactly this already. Ran the APU the interphone was clear as a bell. Tie the AC buses and the noise reapeared, altho not quite as loud as when we were running off external power. So it appears the noise is only present when running of external power or off engine power. Running off APU or battery it's fine. Quote Link to comment Share on other sites More sharing options...
Lucky13 Posted October 13, 2010 Author Share Posted October 13, 2010 Are the headsets plugged into the comm. cords on the quick-don O2 masks? Those cords are not very sturdy. Nope, no cords are plugged in to anything. Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted October 15, 2010 Share Posted October 15, 2010 The "noise" is comming from your Main AC bus. However it is impacting a DC fed system so start to isolate from there. I would start the APU, Tie the AC buses, (this gives you the ESS and Main AC Buses) pull all three of your #1 Main TR Cbers and see what happens. If the issue remains rest them and pull the #2 Main TR cbers and see if the noise goes away.... Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted October 21, 2010 Share Posted October 21, 2010 Any update? Quote Link to comment Share on other sites More sharing options...
tinyclark Posted October 21, 2010 Share Posted October 21, 2010 One/all of those filters are bad, or you have a large AC line running next to interphone lines. But hey, that ain't 'sposed to happen, it's against the rules in the 1-1A-14. Quote Link to comment Share on other sites More sharing options...
Lucky13 Posted October 27, 2010 Author Share Posted October 27, 2010 Sorry for taking so long to post an update. We have traced the source of the noise to J401 PIN C on the bad interphone boxes. This is where the mixed audio comes in from the monitor panel. There is also a wire coming from the recent LAIRCM mod that splices into this wire between the monitor panel and the interphone box. We have also found the annoying loud tone (same 3 boxes, pilot, co and FE) on 3 other tails that were recently moded with LAIRCM. We are trying to research the root of the problem now. Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted October 27, 2010 Share Posted October 27, 2010 Guess this conversation should move into the private networks based on the system in question... Quote Link to comment Share on other sites More sharing options...
Lucky13 Posted October 27, 2010 Author Share Posted October 27, 2010 Soemthing interesting we found was that when the shielding on the wire to PIN C is UNgrounded the noise goes away. When the shield is grounded again the tone is back. Same thing when we just attached a spare length of wire with a pin on it to the cannon plug in pin C. When the shielding is grounded to any location on either end of the wire the loud noise is present, when you remove the shield ground, it's quiet. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted October 29, 2010 Share Posted October 29, 2010 J402, Pin C, mixed audio in? Is this at the pilot's station? Is you pilot's interphone box on the pedestal, or side shelf? I'm a bit confused, since I don't know what pin C you are referring to. Quote Link to comment Share on other sites More sharing options...
Lucky13 Posted November 6, 2010 Author Share Posted November 6, 2010 Yes Pin C, Mixed Audio on the Pilots (side shelf), the Copilots and Flight Instructors interphone boxes all have noise on them. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted November 8, 2010 Share Posted November 8, 2010 Make sure those shields are only grounded on one end of the cable. Check the run of the extension cable from the pilot's side to the pedestal and make sure there are no large AC cables running near it. Quote Link to comment Share on other sites More sharing options...
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