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Old 18-06-2012, 14:35   #1
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Looking for advice - Icom IC-M45 VHF issue

I have an Icom IC-M45 VHF radio that has the following problem. Whenever I hit the mike's transmit button, the unit's display dims by about 50% and the "BATTERY" indicator blinks on the display. I don't have this problem when using using low power, only high power and it's not a battery issue since this happens even when the boat is hooked up to shore power or running with fully charged batteries.

I have had difficulty getting heard on high power but reception is fine so it doesn't look like an antenna problem.

I can easily replace the radio but I want to make sure it's shot before I spend the money.

Anyone have a possible explanation for this problem? It's not even listed in the user manual...

Cheers,

Moxie
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Old 18-06-2012, 14:43   #2
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Re: Looking for advice - Icom IC-M45 VHF issue

I think you have a bad connection somewhere.
When transmitting on high power the VHF draws a lot of current. When you have a high resistance connection the voltage drop is dependent on the current. Transmitting on high is causing the voltage to drop to a low level because of the bad connection.
Try a multimeter on the leads close to the battery. When transmitting on high you will see the voltage drop to say 11v or lower.
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Old 18-06-2012, 14:52   #3
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Re: Looking for advice - Icom IC-M45 VHF issue

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Originally Posted by noelex 77 View Post
I think you have a bad connection somewhere.
When transmitting on high power the VHF draws a lot of current. When you have a high resistance connection the voltage drop is dependent on the current. Transmitting on high is causing the voltage to drop to a low level because of the bad connection.
Try a multimeter on the leads close to the battery. When transmitting on high you will see the voltage drop to say 11v or lower.
G'Day Nolex,

I agree with your analysis, but shouldn't he check the voltage at the transmitter, not near the battery, if he wants to check line voltage drop?

Cheers,

Jim
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Old 18-06-2012, 14:56   #4
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Re: Looking for advice - Icom IC-M45 VHF issue

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G'Day Nolex,

I agree with your analysis, but shouldn't he check the voltage at the transmitter, not near the battery, if he wants to check line voltage drop?

Cheers,

Jim
Oops sorry Jim you are correct I meant to say close to the VHF.
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Old 18-06-2012, 14:59   #5
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Re: Looking for advice - Icom IC-M45 VHF issue

Roger that... I will take a look next time I am on board. I have a voltmeter in the breaker panel which is right next to the VHF unit so it should be easy to check. The connection should not be too hard to check as it goes right into the panel.

Thanks for the tip!

Moxie
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Old 18-06-2012, 15:12   #6
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Re: Looking for advice - Icom IC-M45 VHF issue

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Originally Posted by moxieskipper View Post
Roger that... I will take a look next time I am on board. I have a voltmeter in the breaker panel which is right next to the VHF unit so it should be easy to check. The connection should not be too hard to check as it goes right into the panel.

Thanks for the tip!

Moxie
The voltmeter will not show the problem if the bad connection is closer to the radio. The fuse holder fitted to most of the icom radios for example, some corrosion here will drop the voltage during high transmit, but the panel meter will still read 12.5 v.
One trick is to use 2 fine pins to pierce the insulation near the radio and measure the voltage during transmit. Ideally when you have found the problem you cut the wire and remake the connection although in practice the small holes made by the pins will reseal reasonably well.
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Old 18-06-2012, 15:16   #7
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Re: Looking for advice - Icom IC-M45 VHF issue

Quote:
Originally Posted by noelex 77 View Post
The voltmeter will not show the problem if the bad connection is closer to the radio. The fuse holder fitted to most of the icom radios for example, some corrosion here will drop the voltage during high transmit, but the panel meter will still read 12.5 v.
One trick is to use 2 fine pins to pierce the insulation near the radio and measure the voltage during transmit. Ideally when you have found the problem you cut the wire and remake the connection although in practice the small holes made by the pins will reseal reasonably well.
If worried about the holes in the insulation, put a drop of "Liquid 'Lectric Tape" on them... seals them up effectively.

Cheers,

Jim
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