Icom ic-m55 won't transmit

[Jimbosan]

My old M55 receives nicely and all the functions work, but when I press the mic to transmit the channel# disappears and two horizontal lines appear on the screen, but the tx sign does not. Has anyone seen this type of behavior in a vhf radio ? Is there an easy way to test the mic and cable connection ?

[gonesail]

how old is the mic? i just got a new one from Amazon for 65.00 for my M802.

[tkeithlu]

We've got radio specialists on the forum, and I am not one of them, despite a general license. That said, this sounds like a corroded power connection, such that when you key the mic, needing bunches of amps to transmit, your voltage drops like a rock. Quick likely repair - get some fine sandpaper, and sand the mated surfaces back to the battery.

[Jimbosan]

The mic was replaced by the previous owner about ten years ago. That's why I thought I would like to test it before getting a new one.

[Jimbosan]

Thanks. I'm in the middle of that process now. I haven't investigated the antenna connections all the way up the mast though. Could they cause a similar situation?

[tkeithlu]

corrosion up the antenna linkage should make the antenna impossible to tune, so transmission power drops, but should not shut down the radio.

[pitlaw]

Not sure I understand the facts? Are you saying it doesn’t transmit or you don’t see the transmit symbol while not connected to an antenna. I had the latter experience and found out, through the manual I think, that the symbol wouldn’t show. Check the manual to confirm my recall.

[Scubaseas]

Originally Posted by tkeithlu

We've got radio specialists on the forum, and I am not one of them, despite a general license. That said, this sounds like a corroded power connection, such that when you key the mic, needing bunches of amps to transmit, your voltage drops like a rock. Quick likely repair - get some fine sandpaper, and sand the mated surfaces back to the battery.

This. Likely not a mic issue.

[pitlaw]

Forget my post comment. It’s not on point.

[Redline452]

I had an M55, great little radio. At one point it started acting odd, because the internal 3V coin-cell backup battery had died. It was soldered in, so I replaced it with a coin-cell socket and regular battery (CR2025 IIRC). You might have to do a memory reset after replacing the battery. I think I have a service manual for that radio... somewhere.



Power drop-out is a possibility, make sure it has good voltage *at the radio* while keying transmit. One interesting thing about the M55 - the TX indicator on the display is not activated by the PTT button, but rather a power sensor circuit that checks for actual RF output at the antenna connector. Like I said, nice little radio.

[Brian.D]

Concur, if the display goes blank then you for sure have a power issue. I could be inside the radio. Do you have a spare 12vdc battery you can use for a quick test? Maybe even replace the power cable if it has that ability. If you haven't done this yet, try on 1 watt. That requires less current than 25 watts.

[Jimbosan]

All great suggestions. Thanks. I will continue tracking down the potential power issues. I have a portable, so I can easily check for even weak transmissions.

[mabowers]

Does the unit transmit in Low power mode?

[Scubaseas]

Put a voltmeter on the + and - at the radio and hit the mic button to transmit. Voltage should be essentially the same mic on or off. If it's not follow the + and - connections and wires from battery to radio. Or radio to battery. Could be a bad connection anywhere or bad circuit breaker. If the voltage in transmit is the same the issue is internal to your radio.

[Paul Howard]

I had the same issue with the same model radio, received just fine, try to transmit and nothing.
I eventually traced the wires and found a corroded joint behind the paneling leading to the radio. Ran some new wire and re-did the connections to the radio and it worked fine ever after.