Frustrating radio problem

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Scraping Paint
Oct 23, 2007
After many years of flawless operation the ICOM 502 we installed in our boat developed an odd problem the other month. After about 20 minutes it would lock up. Part of the screen display would go away although the channel number would remain. But none of the radio's operations worked--- it didn't receive, didn't transmit, we couldn't change channels, etc. Turning the unit off and then back on restored complete normal operation for another 15 or 20 minutes at which point it would lock up again.

I removed the radio from the panel and disconnected the Command Mic to see if it was the problem. It wasn't. I checked the power going to the unit and it was a proper 12.5-13 vdc. Even when removed from the panel it exhibited the same lock-up problem after about 15 minutes of operation.

So I took it to the electronics shop in our marina where we had purchased it. Jerry could not get the radio to lock up, even wrapped in a plastic bag to heat it up, until he finally left it on in his shop all day and all night. The next morning he came in to find it in its locked-up condition.

So he sent it to ICOM in Bellevue, Washington. They couldn't get it to quit but after Jerry told them what he had experienced, they put it through a full week of testing in cold temperatures, hot temperatures, vibration, etc. No luck, the radio ran perfectly the whole time.

So they sent it back to Jerry. He got it back right after I left for China for three weeks, so he put it on his bench, hooked it up, and let it run for the whole three weeks. No problems at all. So Monday he put it back on the boat and I'll re-install it this weekend and we'll see how it goes.

Hopefully it will continue to run fine. But if it exhibits the same problem, does anyone know enough about VHF radios to hazard a guess as to which board (function, circuit) in the radio could do this so we could tell ICOM to simply replace the component? Jerry mentioned the microprocessor could be the issue, but I'm curious if anyone here who truly knows about radios has any other ideas. Thanks.

-- Edited by Marin at 15:53, 2008-12-30
Marin - the first thing that I would do is to replace the "memory" battery withing the unit. While I have not worked much on the Icom marine versions I have spent countless hours working on the commercial versions. These units tend to be very similar in design with the frequency range and controls being the big difference. These batteries only last so long and then they tend to create all manner of weird faults when they get old and it sounds as though yours is due for a change.
You should be able to get a replacement battery at any good electronics parts store as they are usually just a single "button" battery that is either soldered in place or else held by small spring clips.
All the best for '09 and good luck with the radio.
John--- Thanks for the suggestion. Since the radio was freezing while it was on it did not occur to me that the memory battery--- assuming the MC502 has one--- could be the problem. Had it lost settings between uses I would have suspected the battery right off. I will bring this up with our radio guy. Thanks again.
My $0.02:

If there are obvious things - like a battery - try them.* Otherwise (much as I hate the "disposable society" thing), replace the radio.* You can pretty quickly go through more than the radio is worth - and even if you don't, you have the problem of not knowing for sure that you really fixed it (that is, you can't really put in a new board where it failed before and works now).

Intermittent problems are SOBs, and they somehow know how to string you along - they always seem to work for a long time after an ineffective repair, making you think that the problem is solved.* They then wait for the most inopportune time to go TU again.

If you really insist on trying to repair it, there's likely to be a controller board that has a microcontroller and*possibly some external memory (though it all tends to be integrated into a single device these days). That's the most likely point of failure.* Second most likely is the power supply board - the supply that runs the micro (probably 1.8 volts, possibly 3.3 if it's a few years old) may be crapping out.
Let's take this discussion in a little different direction also. How many of us have multiple VHF radios? I have my "big" set and one portable on board all the time, 2 portables during longer trips. (I have a portable that I keep at work most of the time) My mounted radio has a remote mic wired to the flybridge for communication up top where I sit during good weather and docking. The remote is a full function with controls for channels, scan, volume etc.

This takes care of most all communication I need. The portables obviously have limited range with low power, comparatively, and small antenna. As I slowly transition to longer and more remote cruising I'm not as comfortable with the portables as backups. I'm leaning towards a second big unit with it's own antenna on the other side of the boat.

The second unit will have it's remote speaker on the other side of the boat for separation of transmissions. That is, I think I plan to keep one on hailing frequencies 9/16 and the other doing the normal scan of working frequencies. In the PNW with the traffic separation zones I like to know who's coming and going. I also like to overhear other boaters as they babble about how crowded each anchorage is, which marina raised their rates this year etc. Since I monitor and talks on multiple channels at work it is no problem to subconciously monitor the radio on the boat. Yes, is does drive the Admiral crazy but if I keep the volume low, she puts up with it.

I don't intend to wire the flybridge with the second radio. My thoughts for the radio are the same as for the radar. I'm only up there when things are going well. If radio #1 were to go gunnybag and I needed longer range comms, I'd go below. If I really need the radar, I'm never on the flybridge anyway. (I have a separate chart plotter up top for navigation.)

My intent is to mount both radios above the helm (one is currently there) one above the other. Will I experience any interferance from them being mounted this way? Or should there be some separation between the boxes. I think I need to make sure the antenna wires don't run parallel, how about power supply? For redundancy I plan to make a separate power feed from a different circuit, will the power running parallel cause problems?

We have plenty of VHF radios on the boat including a handheld with an adapter cable that can connect it to our 20' primary antenna. This gives the handheld great range although of course it doesn't do anything to increase its transmission power.

But the 502 is our primary radio and I'd like to keep it as long as fixing it doesn't start getting close to the cost of replacing it. A direct replacement (the 504) would run in the neighborhood of $300. Since the ICOM repair facility is within a few miles of where I live, I don't have to contend with packing and shipping to send it in for repair or a component replacement.

Anyway, we'll keep investigating the problem.
Ken -

Having the radios fairly close together isn't likely to be a problem, and running power cables together shouldn't be much of an issue - though I'd sure suggest trying them in the same configuration you're going to mount them before cutting or drilling anything.

Mutual interference is usually caused by very low level radiation back from the receiver input - there can be some bleed through, usually from the first mixer stage, that could give some problems.

The things that you should do:
- use a top quality coax like RG142 or RG400 and not RG58.* It's about 10x as expensive, coupla bucks a foot.* The radio shops will probably scoff at your doing so, but the fact that it's ultra low loss means that there is also ultra low coupling in any areas that the coax needs to be routed near each other.
- use a top quality crimped coax connector, preferably with gold plated center contacts (if it's a BNC).
- keeping the coax as separate as possible is good, too.
- keep the two antennas as far apart as possible.
"PMM Cheerleader" I love it! Hahahaha!
Is there a spam filter on this forum somewhere. I seem to be getting some unwanted bleedover from other sites............
Yea, it really gets to be spam when he posts under "fuel check" and says he has no experience with fuel prices, but here are some articles.......
Just a note for folks that use #13 the lock or bridge freq.

Every US set will only transmit on 1W low power on this freq.

IF you have a fine Digital (or cheaper ) antenna that has high gain , but is lowered to allow passage under bridges , the radiation may be so poor that even within eye contact the bridge cant hear you.

Our solution is to use one of the hand held units, but a far better solution is a sailboat base loaded small antenna (masthead style) mounted high as you can.

This will allow 3 or more mile communication with your regular VHF,, and could save a half hour as the lock master readies the pond for you.

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