Bods Posted December 22, 2009 Share Posted December 22, 2009 Been working this for about a week now. Little background on it. The plane left for depot two months ago with no hf problems, nothing in the previous 4 months as well. It landed at depot with #2 hf coupler fault and no tune tone. Depot serviced the coupler and were able to clear the fault and get the tune tone back, but they weren't able to transmit, blamed it on atmospherics :confused:, and wrote it up for an in-flight check. It landed back here with the no transmit problem. It tunes just fine, breaks squelch, no faults in any freq range, receive is crystal clear, just no transmit and no sidetone. We've swapped or replaced r/t's, r/t mounts, couplers, interlock relays, #2 rf interlock relay, secure interlock relays, secure processors, secure rcu's, and control panels. This is a non scns a/c. We've checked the capacitor in the junction box, the dummy load at the coupler, the lightning arrestor, and numerous mic and tx aud lines between the interphone junction box, rt, and coupler. When listening in from another a/c, you can hear it break squelch, then there's a loud high pictched hum/feedback like noise, but very very faintly (like hearing test faint), you can hear the operator asking for an hf check. I'm at a loss for where to go with this. It's one of the stranger hf problems I've encountered. Any help would be much appreciated. -Bods Quote Link to comment Share on other sites More sharing options...
bryanball Posted December 22, 2009 Share Posted December 22, 2009 I would start right back at the interlock relays. Make sure the diode is good on each and double check the wiring locations. Also cut off any heat shrink from around the antenna line connectors and make sure they are tight. Make sure you do it all yourself, turnover seemed to cause alot of problems I encountered. Quote Link to comment Share on other sites More sharing options...
Guest Posted December 22, 2009 Share Posted December 22, 2009 Feed back from a co-worker. He said it may seem simple but.... On the RCUs, is the switch in bypass when transmitting? Quote Link to comment Share on other sites More sharing options...
Bods Posted December 22, 2009 Author Share Posted December 22, 2009 Feed back from a co-worker. He said it may seem simple but.... On the RCUs, is the switch in bypass when transmitting? Man, I wish that was it. That would have made my life really easy. We checked that when we first got the problem. We've swapped around all the secure equipment as well. Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted December 22, 2009 Share Posted December 22, 2009 Sounds like your radio is Tx'ing if the "other" aircraft can hear the operator requesting a check... just not enough "power" excaping the aircraft... From what I remember key #1 HF and #2 Ant is switched to the dummy load to prevent a "loop" between the two radios (if they are on the same freq) and vice versa. Maybe you are TXing into the dummy load and that is causing the reduced output. Dont remember the switchology so I would have to look it up.... Long wire or Flush mount Ant's?---- (Long Wire, my guess) Quote Link to comment Share on other sites More sharing options...
INS/Dopplertroop Posted December 23, 2009 Share Posted December 23, 2009 The dummy load switching mentioned prior is a good call to check. Also, were the Antennas removed at the depot or anytime immediately prior to the malfunction occurring? I seem to recall a similar transmission problem on a C-5. The C-5 HF Antennas are both part of the leading edge of the lower part of the vertical stabilizer. In this case the problem was found to be a prior mis-installation when metalic, conductive mounting screws were used, causing the antenna to be grounded to the aircraft skin. Check to see if your HF antenna mount screws aren't supposed to be nonconductive. Quote Link to comment Share on other sites More sharing options...
Bods Posted December 23, 2009 Author Share Posted December 23, 2009 Sounds like your radio is Tx'ing if the "other" aircraft can hear the operator requesting a check... just not enough "power" excaping the aircraft... From what I remember key #1 HF and #2 Ant is switched to the dummy load to prevent a "loop" between the two radios (if they are on the same freq) and vice versa. Maybe you are TXing into the dummy load and that is causing the reduced output. Dont remember the switchology so I would have to look it up.... Long wire or Flush mount Ant's?---- (Long Wire, my guess) We checked the #2 dummy load for this exact reason, but of course it checked good. I'll have to check the #1 as well, didn't think to check that one, thanks. Right now I'm ready to try just about anything. And yes, you are correct in assuming that we have longwires. Man I wish we didn't. The dummy load switching mentioned prior is a good call to check. Also, were the Antennas removed at the depot or anytime immediately prior to the malfunction occurring? I seem to recall a similar transmission problem on a C-5. The C-5 HF Antennas are both part of the leading edge of the lower part of the vertical stabilizer. In this case the problem was found to be a prior mis-installation when metalic, conductive mounting screws were used, causing the antenna to be grounded to the aircraft skin. Check to see if your HF antenna mount screws aren't supposed to be nonconductive. It only went to depot for an iso (our iso dock was booked solid) and I dont believe they removed the masts, but I'm pretty sure that even if the screws were conductive on them, it wouldn't matter because the mast itself is mounted to the a/c skin. We inspected and reseated the lightning arrestor and found nothing wrong. Quote Link to comment Share on other sites More sharing options...
FlyeRick Posted December 23, 2009 Share Posted December 23, 2009 You're obviously keying the radio & transmitting. I'd recheck the tx audio lines & ensure none are shorted to shield. Rick Quote Link to comment Share on other sites More sharing options...
KF4DVG Posted December 23, 2009 Share Posted December 23, 2009 How about a Thru-Line wattmeter at the R/T...to see if any modulation (tx audio) is getting to the R/T and creating an RF (swing) output... Quote Link to comment Share on other sites More sharing options...
Bods Posted December 24, 2009 Author Share Posted December 24, 2009 Thanks for all the ideas guys. I havn't been able to work it the past couple days due to some other mx being done on the plane which limited the amout of troubleshooting we could accomplish. I'm off for the next week, which I have to say, I'm looking forward to very much. Havn't had a day off in a couple weeks. I'm turning over this writeup to my new years shift and passing along all of your recommendations. Hopefully a fresh set of eyes will help. When we do get a fix, I'll be sure to post it so that in the future if someone else has a similar writeup they can have something that could hopefully help. Once again, thanks for your help. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted January 2, 2010 Share Posted January 2, 2010 99.9% sure it is a transmit audio line. If it were an antenna problem, you would be getting a tune tone every time you key it, since it couldn't tune properly. If the antenna cables were swapped on the coupler mount antenna coax relay, that would cause that small dummy load to heat up pretty quickly. Does it sound differently when transmitting on CW? If it transmits, all interlock relays are working. What particular aircraft is this, and old ABCCC? Tail number? There is the KY bypass relay (maybe not on this bird), has it been checked? Are there any HF #2 toggle swithes to use that HF2 position for another radio, like the VHF FM? Any time I have a loss of transmit audio, here's what I do. Go to the IJB and disconnect all transmit audio (mic) lines coming from all the ICS boxes except for the pilot's, and op check it with only that mic line connected. If one of the mic lines is bad, you should be bale to find it with a DVM as well. Sounds to me like there is a shield short on one of them. Please let me know what aircraft you are working on and maybe I can come up with a few more ideas. You can also e-mail me at Moody, under the name clark, tiny. Quote Link to comment Share on other sites More sharing options...
Bods Posted January 6, 2010 Author Share Posted January 6, 2010 99.9% sure it is a transmit audio line. If it were an antenna problem, you would be getting a tune tone every time you key it, since it couldn't tune properly. If the antenna cables were swapped on the coupler mount antenna coax relay, that would cause that small dummy load to heat up pretty quickly. Does it sound differently when transmitting on CW?. Hey Tiny, thanks for all your ideas. I've been set on it being a tx aud line since the start, but still havn't found anything. We checked the dummy load, which checked good, but havn't tried it in CW yet. It's been tough to get a chance to work this bird. Com/Nav usually gets the short end of the stick when it comes to maintenance priority. What particular aircraft is this, and old ABCCC? Tail number?. You're close, it's a Blk 35 BS1 EC-130, Tail# 1595. There is the KY bypass relay (maybe not on this bird), has it been checked?. We swapped the secure bypass relays already as well as all the secure components, which didn't do anything. I suppose we could check the plugs there too. Are there any HF #2 toggle swithes to use that HF2 position for another radio, like the VHF FM?. Yes it has toggle switches at each station for the AITG radio. Any time I have a loss of transmit audio, here's what I do. Go to the IJB and disconnect all transmit audio (mic) lines coming from all the ICS boxes except for the pilot's, and op check it with only that mic line connected. If one of the mic lines is bad, you should be bale to find it with a DVM as well. Sounds to me like there is a shield short on one of them.. We did this the other day with no change, we're going to move on to the mission interphone system next (back end). Please let me know what aircraft you are working on and maybe I can come up with a few more ideas. You can also e-mail me at Moody, under the name clark, tiny. Thanks again for your help. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted January 7, 2010 Share Posted January 7, 2010 I don't have your exact diagrams probably, but most of the XMIT audio is set up like on the attached, very crude, drawing. Quote Link to comment Share on other sites More sharing options...
Bods Posted January 26, 2010 Author Share Posted January 26, 2010 Thanks all for the help. We've been swamped with work here for the past few weeks, but we finally fixed this hf problem last night. We were told that the capacitor had checked good early on in our troubleshooting and never looked at it again... until last night. We got a new capacitor in there and voila. HF works. Go figure. So in conclusion, HF#2 no sidetone, rx ok: corrective action is replaced capacitor C20RB Thanks again!!!:D Quote Link to comment Share on other sites More sharing options...
Bods Posted January 26, 2010 Author Share Posted January 26, 2010 By the way, Tiny, I've been instructed by my com nav counterparts to inform you, that you are the man :cool: Quote Link to comment Share on other sites More sharing options...
tinyclark Posted January 26, 2010 Share Posted January 26, 2010 Not really, I've just been doing this for too long. Did I mention I get to RETIRE this year????? Woohoo!! Quote Link to comment Share on other sites More sharing options...
KF4DVG Posted January 27, 2010 Share Posted January 27, 2010 Glad to hear that you guys got it licked. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted January 27, 2010 Share Posted January 27, 2010 By the way, Tiny, I've been instructed by my com nav counterparts to inform you, that you are the man :cool: I sent you a private message about your wiring diagram. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted January 27, 2010 Share Posted January 27, 2010 Ya know, your problem got me to thinking, which I try to steer away from, but I did it anyway. I couldn't remember having a capacitor on the mic line in the shop while working on the ARC-190, so I didn't understand why they needed one on the aircraft on a new system. I looked at the TCTO that installed the ARC-190 1c-130-1199, and guess what I found... they were supposed to have been removed!! Quote Link to comment Share on other sites More sharing options...
Bods Posted January 28, 2010 Author Share Posted January 28, 2010 Ya know, your problem got me to thinking, which I try to steer away from, but I did it anyway. I couldn't remember having a capacitor on the mic line in the shop while working on the ARC-190, so I didn't understand why they needed one on the aircraft on a new system. I looked at the TCTO that installed the ARC-190 1c-130-1199, and guess what I found... they were supposed to have been removed!! Wow, I never heard anything about that. I'll have to ask around see if anyone here remembers that coming down. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted January 28, 2010 Share Posted January 28, 2010 TCTO 1199 was done in 1989-91, replacing the old 618T vacuum tube radio. That's what I'm saying, the caps should have been removed at that time. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.