Narco MK12D/R Audio Problem

AKBill

AKBill

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AKBill
Hi, Been having an intermittent problem with my Narco NAV/COM audio. Was wondering if anyone can help trouble shoot this radio.

The problem is intermittent, Every once and a wile when returning to home class D, I try to contact tower and get no response. So I change to number 2 Com report position and land. Was told my PTT switch was the problem so installed new PTT switch.

So I go flying and returned to field, I had contacted tower and was told to report 1 mile south. I reported but no answer from tower. Tower told me they had a carrier signal but no audio. After landing I checked connections and contacted ground for radio check. They said radio sounded good. So I figured I had a bad connection.

On a flight a couple of days later the problem reoccurred, when returning to field. Once again after landing I checked connections and called for radio check, worked fine. I don't think its bad connections!!

Over Christmas I rented space in a heated hanger and checked all connections to radio, intercom (Flight Com Portable), and PTT switch everything looked good. Left radio on for 2 hours and used a handheld as a receiver and talked to myself for 30 min, could not get problem to reoccur.

The last flight I removed intercom and did some pattern work, no problems.

I don't trust the Com 1, weather has been bad lately and I have not flown in 2 weeks. Problem only occurs after flying for 30 min or more.

There are no avionics support at home field. There are a few part 121 operators on field but they don't like to get involved with the GA folks. To busy with there own planes.

What is the best way to troubleshoot this intermittent audio problem?

Thanks
Bill B.
 
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Well, I know you don't want to hear this but since the com 2 is working flawlessly(I presume) that pretty much leaves it inside the Narco, which I presume again is your com 1 and is being balky.

Failure to transmit can be caused by a ton of different things, but usually it's with the power transmitter circuit. Although it could be in the audio combiner, or even the audio primary amp which takes the feed from the mic and amplifies it slightly before combining it on the carrier wave. Lots of things to check, and lots of things to repair, and if it's intermittent you don't know until you don't know.

I have several Narco products in my panel and when they no longer are suitable for aviation reliability they are going in the junk pile. Narco is dead, and finding someone who is willing to work on them is increasingly difficult, if not impossible. My HSI is a Narco unit, and I'm giving it maybe one more year before I toss it, even though right now it's working great.

I believe there is a slide in replacement for the 12D from TKM, but don't quote me. As a last resort, the slide in contactor at the back of the radio tray is a common area of contact failure. Remove the radio from the tray, using a can of Deoxit (http://www.deoxit.com/) found at any radio shop spray the socket connections in the tray back. Also spray the plug connections on the back of the radio once out of the tray. Inspect the connections with a bright light and look for any dark red, or green/brown goo on the contacts. If it's all clean, slide it back in and give it another test.
 
If the radio is clearly going into transmit mode (you see the little "T" in the display), then I'd seriously look into the audio panel.

A little more info would help, too. Tell us about your setup; what audio panel, is there a separate intercom, what are the two Nav/Coms?
 
Cowboy- I had a MK12A originally and had it change out with the MK12D/R 16 years ago. The radio has pig tail leads from back of radio. No contacts in tray.

Very frustrating works great then transmits carries only with no voice. I'm thinking its in the radio!!!!
 
Spike-- #1 NAV/COM is Narco MK12D/R it replaced the MK12A. #2 NAV/COM is King KX170B, no real audio panel. Toggle switches to select com1/com2 and toggle switches for com1 speaker/phone and toggle switch for com2 speaker/phone

I have a separate intercom Flight Com portable. Could there be a problem with it causing the audio problem?

I think I always see the "T" transmit light on radio. Problem is when this happens I'm coming in to land, and switch to com2 to reestablish communications with tower.
 
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I had a similar setup..a radio shack A/B switch with narco 12D. Only the Com side worked so I got the tkm replacement. The original was the monster round connector so I let the shop re-work for slide-in, made life much simpler. The TKM radio has been bullet proof for almost 15 years.
 
Murphey---I am with you, I would love to change out. Sure would hate to fly 8 hours to Anchorage or 9 to Seattle to have work done. No real support here. I guess I could beg and plead with local Part 121 operators to help me out but the are not keen on working on GA aircraft!!!!
 
AKBill said:
Murphey---I am with you, I would love to change out. Sure would hate to fly 8 hours to Anchorage or 9 to Seattle to have work done. No real support here. I guess I could beg and plead with local Part 121 operators to help me out but the are not keen on working on GA aircraft!!!!
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Bottle of god single malt? Couple 6packs of quality beer? Home made Chocolate chip cookies? Cash? TKM is in Arizona, will happily ship anywhere. I've noticed there's not much difference inprice of between eBay and new.

Is there a military base nearby? one of the avionics techs might be interested in a weekend job.
 
Yah no problem with getting the radio here. Installation is the glitch. No military base here. Commercial part 121 carriers is by best bet.

Just wondering if it is the intercom. My last flight was not long 3 touch and goes. Took the intercom out and just used a headset.

On second thought it isn't the intercom if com 2 works
 
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AKBill said:
Cowboy- I had a MK12A originally and had it change out with the MK12D/R 16 years ago. The radio has pig tail leads from back of radio. No contacts in tray.

Very frustrating works great then transmits carries only with no voice. I'm thinking its in the radio!!!!
Click to expand...

Time for do-over. Aviation is not free, or even cheap. If I may recommend, I would get the Apollo GX-60 or 65 panel GPS/comm with tray and antenna. Rip the Narco and do it right. It's not color, but decent cost. Sadly, the Apollo is also orphaned, but the data cards are still supported well.
 
Thanks for the input Cowboy--I'm thinking you are right. Changing out with something new. Going to have to start begging the part 121 guys to do the work
 
If you don't need or want the enroute GPS, you can go with the TKM deal as the best bet in cheap nav/com I think. They are made in AZ USA. I don't have any association with them, but they work well. http://www.aircraftspruce.com/pages/st/manu_tkm/mx300.php You can source a tray for a ARC 300 or 500 series anywhere pretty cheap, try www.asod.com for a tray, I think they have bunches.
 
It's not necessarily the radio itself but given the fact it's a 12D I'd put a strong guess it's there. What unreliable pieces of crap those were.

I had comm1 turn into a kazoo and it turned out to be the Garmin audio panel.
 
Thanks Cowboy--I really don't want to rework the whole panel. I would love to get rid of the A/B toggle switches and get a real audio panel. Guess I need to take out a second mortgage on the house!!
 
AKBill said:
Hi, Been having an intermittent problem with my Narco NAV/COM audio. Was wondering if anyone can help trouble shoot this radio.

The problem is intermittent, Every once and a wile when returning to home class D, I try to contact tower and get no response. So I change to number 2 Com report position and land. Was told my PTT switch was the problem so installed new PTT switch.

So I go flying and returned to field, I had contacted tower and was told to report 1 mile south. I reported but no answer from tower. Tower told me they had a carrier signal but no audio. After landing I checked connections and contacted ground for radio check. They said radio sounded good. So I figured I had a bad connection.

On a flight a couple of days later the problem reoccurred, when returning to field. Once again after landing I checked connections and called for radio check, worked fine. I don't think its bad connections!!

Over Christmas I rented space in a heated hanger and checked all connections to radio, intercom (Flight Com Portable), and PTT switch everything looked good. Left radio on for 2 hours and used a handheld as a receiver and talked to myself for 30 min, could not get problem to reoccur.

The last flight I removed intercom and did some pattern work, no problems.

I don't trust the Com 1, weather has been bad lately and I have not flown in 2 weeks. Problem only occurs after flying for 30 min or more.

There are no avionics support at home field. There are a few part 121 operators on field but they don't like to get involved with the GA folks. To busy with there own planes.

What is the best way to troubleshoot this intermittent audio problem?

Thanks
Bill B.
Click to expand...



Bill - I have a Narco Mark 12D+. Your problem is very similar to the one I am currently having it serviced for. The problem is with the modulation circuit. A problem I am told is common with these Narco radios.
 
Marauder said:
Bill - I have a Narco Mark 12D+. Your problem is very similar to the one I am currently having it serviced for. The problem is with the modulation circuit. A problem I am told is common with these Narco radios.
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Were did you sent the radio for repair? What is the expected cost of repair? I was afraid I would have a hard time finding someone to work on it. Thanks for the info.
 
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AKBill said:
Were did you sent the radio for repair? What is the expected cost of repair? I was afraid I would have a hard time finding someone to work on it. Thanks for the info.
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I will be checking up on mine tomorrow and let you know if anything changes from the information I gave you.
 
Marauder said:
I will be checking up on mine tomorrow and let you know if anything changes from the information I gave you.
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Thanks again for the info. Let me know what they found. PM me if you like. They are calling for clearing weather tomorrow. I may even get to fly and check out this radio some more.
 
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I have 2 narco 12d in my airplane. Com 2 cannot be heard by atc. I am modulating but mike sounds under water. I swapped the cables in the back and the problem followed the radio. So I suspect I have the same problem. The T shows when I PPT. But I am transmitting 3 by 5 and not readable. The other comm is 5/5. I am running it through PSEng audio panel. Please update this if you get a solution
 
Patrick evans said:
I have 2 narco 12d in my airplane. Com 2 cannot be heard by atc. I am modulating but mike sounds under water. I swapped the cables in the back and the problem followed the radio. So I suspect I have the same problem. The T shows when I PPT. But I am transmitting 3 by 5 and not readable. The other comm is 5/5. I am running it through PSEng audio panel. Please update this if you get a solution
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Patrick, not that it's not possible, but the thread you replied to is well over five years old. @AKBill is still around these parts... hopefully he see this and let you know what transpired back then. Good luck.
 
Ditto here. Narco MK12D and having the same intermittent transmitting issues. Shows the T transmit and others can hear the click of the radio, but no voice. Got bad enough that we are hoping to get out AP/IA to approve a switch to a Garmin GTR-200 (experimental) radio with integrated intercom. We figure we can do the install during this months annual ourselves.
 
A couple of relatively easy things to check. The fact that you're getting a "T" transmit indication only means that the PTT switch is successfully grounding the tip terminal of the mic plug/jack. The voice signal is carried via the ring terminal. If any of the mic jacks in the system are accidentally grounded or not installed with insulating shoulder washers, you might have the issue you both have described. Check for continuity between the ring terminal of your mic jack to the audio panel or com, and also make sure the mic jack barrel terminals are not grounded directly to the airframe.. they should return to your intercom, audio panel, or com. I solved a similar issue recently for my CFI in an Arrow.... the auxiliary handheld mic jack was wired in parallel with the pilot's PTT switch and mic jack, but it was grounded. No one could hear the pilot talk, although the PTT switch registered as transmitting when depressed. I disconnected the incorrectly grounded aux mic jack, and problem was solved.
 
Don’t know if it still matters to anyone but I have a fair amount of experience working on mk12d radios.
As one member stated it could be a number of things. So far I have worked on two of these that have a transmit carrier but no modulation or intermittent modulation. In both of these the problem is caused by the 12 to 28 volt boost converter not working. This applies to the 14 volt radios only. The modulator uses high level AM modulation meaning that an audio amplifier drives the final RF amplifier to modulate the carrier signal. If the boost converter power transistor fails open, typical, then the audio circuits get 12 to 14 volts instead of 28 volts. The modulator audio amplifier barely works at this voltage and sometimes does t work at all into the load it drives. It is likely that the receive audio level may be weak as well. On mine the boost converter power transistor is blown. It’s not easy to get but I found some on EBay for a reasonable price. I’m an electrical engineer with years of RF communications experience. I do not suggest you try fixing this by yourself unless you have good electronics skills and appropriate test gear. The service manual is available on the net. Best wishes.
 
I'm having this exact issue. Would you mine sharing the link to the boost converter power transistor? My radio works perfect on the ground but when I take off is when I get the problem. I'm assuming once airborne the voltage drops and is not receiving the voltage it needs. Any and all help would be appreciated.


Martin Armfield said:
Don’t know if it still matters to anyone but I have a fair amount of experience working on mk12d radios.
As one member stated it could be a number of things. So far I have worked on two of these that have a transmit carrier but no modulation or intermittent modulation. In both of these the problem is caused by the 12 to 28 volt boost converter not working. This applies to the 14 volt radios only. The modulator uses high level AM modulation meaning that an audio amplifier drives the final RF amplifier to modulate the carrier signal. If the boost converter power transistor fails open, typical, then the audio circuits get 12 to 14 volts instead of 28 volts. The modulator audio amplifier barely works at this voltage and sometimes does t work at all into the load it drives. It is likely that the receive audio level may be weak as well. On mine the boost converter power transistor is blown. It’s not easy to get but I found some on EBay for a reasonable price. I’m an electrical engineer with years of RF communications experience. I do not suggest you try fixing this by yourself unless you have good electronics skills and appropriate test gear. The service manual is available on the net. Best wishes.
Click to expand...
 
Travis Ashby said:
I'm having this exact issue. Would you mine sharing the link to the boost converter power transistor? My radio works perfect on the ground but when I take off is when I get the problem. I'm assuming once airborne the voltage drops and is not receiving the voltage it needs. Any and all help would be appreciated.
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I don’t think the problem is the boost converter if it transmits fine on the ground but not in the air. That is truly strange. I can’t think of any reason there would be a difference in the air unless engine vibration is causing a connection to fail somewhere. Can you give more information on the exact problem and under what conditions you are testing? Thanks
 
Hi thanks for the reply. So I have tested this radio on ground and in air. On the ground I'm able to transmit with no issues. When I get in the air I see that I'm transmitting but no modulation. Others csn hear me engage the radio but there is no voice being carried and I have no sidetone at all. Sometimes it comes back sometimes I have to use my backup radio. I must also say that I can always receive on the radio but transmitting is where it is intermittent.
 
Hi. The sidetone audio does come from the modulator audio signal so I believe you are correct that there is no modulation. My best guess is there is an intermittent connection in the modulator audio path that comes and goes with engine vibration. It could also be the boost converter being intermittent since receive audio still works even if the boost converter does not. I think it’s time to put that unit on the bench. Do you have experience working on electronics and have test equipment? If not I can’t think of anything else I can do to help you. The service manual is available on the internet but won’t help unless you can read schematics. BR, Martin
 
Travis Ashby said:
On the ground I'm able to transmit with no issues.
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Is this an ongoing problem or a new problem? And just to add, ensure the radio is fully seated in the rack. If need slide radio out and check pins then reinstall. Then check for corrosion, etc. between the antenna and the airframe ground plane.
 
Marauder said:
Bill - I have a Narco Mark 12D+. Your problem is very similar to the one I am currently having it serviced for. The problem is with the modulation circuit. A problem I am told is common with these Narco radios.
Click to expand...

Plus one on the above. I was on flight following and tried acknowledging a radio call from center. Center heard the carrier signal but no voice. I squawked 7600 and they figured out I was unable to answer. Sent the radio into NARCO when they were still in business and they confirmed it was the modulation circuit. Worked like a charm when it returned and it went with the airplane when it was sold.
 
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