Testing an Icom 504 VHF with External Mic

[bcalfee]

I have a ICOM 504 installed at my nav station with an external mic in the cockpit. We have had problems intermittently with the cockpit MIC. I can't figure out what the problem is.

I sent the MIC back to ICOM and they said it was OK.

We recently had an emergency problem and called the coast guard and then for anyone on 16... from the cockpit. No response. We survived... then when we were following the coast guard to a harbor, we were experimenting with the various mics. the one below was perfect and the one in the cockpit was weak and unreadable. Thinking maybe it was the wind, I moved under the dodger and they read me loud and clear.

So, was it the wind or moving the mic, ie a connection issue. i would like to trouble shoot it... Does anyone have suggestions on how to troubleshoot this remote mic?

[GordMay]

Microphone Testing:
➥ Microphone Pinout Testing - Zero meter deflection (pointer to left) indicates Short Circuit or Zero Resistance. Full deflection (pointer to right)indicates Open Circuit or High Resistance Cruisers & Sailing Photo Gallery

[fairbank56]

Which version of the 504? The one with external microphone pigtail jack on the back or not? If not, assume you are using a commandmic for the cockpit mic? Which one, II or III? If your using a commandmic, the info that GordMay gave you is of no use as the commandmic is not a simple standard microphone.

Eric

[drinky]

I had a 505 set up the same with the same problem. Turns out the cable that joins the set to the command mike had been cut to get it to the nav station and rejoined and in the process the thin wire had a problem somewhere in its length, not in the join. New cable routed so it didn't need to be cut solved the problem.
Drinky

[fairbank56]

I have found this to be a common problem with commandmic cables. Both the coiled cord from the mic itself as well as the radio to mic jack cable. I'm a service tech and have repaired several commandmicIII cables. I believe this is a manufacturing defect that causes the cable to fail about an inch or two from where the cable enters the handset. This part of the cable is straight (before the coiled part) and is long enough that it can be cut and reinstalled into the handset. This is a ten conductor cable with six of them being a very small 26 gauge wire. The wire that fails most often is coaxial (wire with shield around it) and is used for both receive and transmit audio. My theory is that a pull test is applied to this cable to test the integrity of the strain relief parts of the handset and this stretches the wires within the cable. After a period of time where the cable gets pulled and twisted during normal use, the copper wire parts, still within its insulation, and then operates intermittently. This is how it has appeared upon dissecting the cable. Another design flaw with this radio is that the power feed wires within this cable are not fused inside the radio. A short circuit of these wires or partial short as when water gets inside the exposed commandmic jack causes a transistor in the radio to overheat and slowly cook a circuit board in the area where the transistor is mounted.

Eric

[bcalfee]

Yes, this is a ICOM 162B which is the Comandmic III. There is a separate connection on the back of the radio for this. When I first installed the MIC I had the connector under the dodger... so when I was at the helm and needed to talk, I had to stretch the coils out... And I as worried about that. SO I sent the Comandmic back to ICOM to have it check. They said there was no problem. I am still concerned about that stretch. I have moved the connector so it is now in the top of a cubby closer to the wheel...

[fairbank56]

The question is, is how well did Icom actually test it? Simply plugging it in on a bench test setup and testing it without stressing the cord is not good enough.

Eric

[bcalfee]

Well, I have sent it back with a long letter explaining the issues and requesting a more thourough testing than before... I did not pull out the cable that runs from the radio to the MIC as it runs behind the panel that is behind the Nav station... If I take all that out, I only want to do it once, maybe to replace the cable, If they say everything is great with the radio and remote. Thanks to everyone for comments

[Badsanta]

I have had the same intermitent problems with mine. I think it is the connection that you plug the mike into not the mike and its cord. The extention from the radio to the external cockpit plug.