radio install troubles

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Gene Sullivan

Filing Flight Plan
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Jul 16, 2021
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Gene Sullivan
I am installing a used MX 300 radio in my musketeer the radio uses a ARC in525a course indicator I have downloaded the instruction manual for the ARC RT328T radio the MX 300 is a direct replacement radio I have all the original wire bundles that came out of the donner aircraft I have wired the installation per the 328T manual I will try to up load the wiring diagram am an A/P I/A and have been working on aircraft for over 50 years the problem I am having is the two/from flags always shows' off and every now and then will momentarily show to or from and goes back to off I have checked and checked agen the wiring from the radio rack to the course indicator I have sent the indicator off to be checked it was returned to me with no defect noted I have also tried another MX300 radio same problem I must be missing something but it is driving me nuts also when I try the VOR test button I get a good needle swing but the flag remains off the com side of the radio works great any help would be welcomed
 

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Gene Sullivan said:
I have all the original wire bundles that came out of the donner aircraft
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Gene Sullivan said:
the problem I am having is the two/from flags always shows' off and every now and then will momentarily show to or from and goes back to off
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Need to PM @Jesse Saint for input. He's the resident sparkie. But in the mean time since the flags do move have you megged any of the harnesses? Are the connectors soldered pins or crimped?
 
Have you checked the pins on the back of the radio and the connector in the rack? Wouldn't hurt to shoot some contact cleaner in there.
 
Throw that old junk back in the trash can you dug it out of.
 
new nav antenna new diplexer tried hooking up nav antenna straight to the nav connection same results
 
Papa Pilot said:
Have you checked the pins on the back of the radio and the connector in the rack? Wouldn't hurt to shoot some contact cleaner in there.
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all connections have been checked and rechecked all connections have good conductivity between radio connector and VOR/ILS head
 
all the connections have been checked more then once I have checked them with a VOM several times I also subbed a second MX300 radio in to see if it was the radio new nav antenna new diplexer all new 400 coax cable checked all the wire that should be shielded is correct sent the VOR/ILS head to be checked report said it is good I know I am missing some thing but I just don't know what
 
Gene Sullivan said:
all the connections have been checked more then once I have checked them with a VOM several times
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FYI: while a VOM is great at continuity it won't show any issues with degraded insulation or a compromised conductor. If your donor harness is old and now has been manhandled twice during the removal/reinstallation process there maybe a problem in the harness or at the connector pins. If you're positive the system units are serviceable and the system is connected and routed properly then you may want to reexamine the integrity of the harnesses. One method is to use a megohmmeter to find discrepancies that a VOM will not. However, if your unfamiliar with its use you will want to seek some assistance as you can damage things if used improperly.
 
When the flags cycle to “to & from” and then back to off, is that repeatable? Is there something that you can do to repeat the cycling?
 
Without being right there with you and seeing the problem. Have you tried to see what the Flag output drive voltage is from the MX 300? Also maybe check the Flag coil resistance on the ARC in525a course indicator. Not sure what they are supposed to be but if you can find those specs then maybe you can isolate the problem.
 
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