Light Aircraft Association

I have finally bitten the bullet and "invested" in an Icom IC-A220 (plus MBA-3 adapter) as a direct replacement for my BendixKing KY97 (which never missed a beat and worked perfectly)....
Having fitted the ICOM Radio (& MBA-3 adapter), the radio will not transmit, when the PTT is despressed the radio appears to make a noticable noise (like its trying to transmit), however the "Tx" does not illuminate on the LCD display, and no transmission goes out.
Has anyone else used the ICOM IC-A220 as a direct replacement for the King KY97 ? and if so could you let me know which setup options you had to use to get it all working successfully please ?
Thanks for any help / advice....
Andy Smith
1960 Emeraude

I too have just installed the Icom IC-A220 but mine was a completely new install so not an upgrade like yours. I was told some years ago that the King 97 was in fact an Icom IC-A200 but with a different front panel - if so the 220 with the MBA-3 should be a straight replacement.

I am by no means an expert on radio installations but I wonder if the problem could lie in the way the PTT line was connected on the old installation. As a first trial I would be inclined to try an experiment by disconnecting the PTT line on pin 9 then connecting a test length of wire and seeing if grounding that makes the tx icon on the display light up.

Hi folks I seem to remember that my friend had the same issue and he eventually had to fit an external relay to the PTT line... Cant remember all the details but will ask Keith next time I talk to him.

Hi,
I have had similar issues with the A220 that have taken a very long time to track down.
I do not use the MBA-3 adapter but the symptoms seem similar in that I had perfect reception but no ability to transmit.
My avionics guy suggested the following that seems to have cured the problem.
Take the "ground" side if the PTT switch diectly to the negative battery terminal, don't use any other "grounding" point.
Make sure that the mic socket(s) are fitted with the supplied black fibre insulation washers, thus insulated from the airframe.
Take the mic "screen" wire ONLY to pin 9 on the Icom D-sub 25 way connector (don't connect it to any other ground/earthing point on the aircraft). Thus the screening is only connected at one end.
Take the mic socket(s) wires directly to pins 10 and 11 on the Icom D-sub 25 way connector.
It seems that the A220 is extremely sensitive to induced ground loops.
If you can receive ATC but not transmit, the problem is on the mic wiring side.

We did the same swap with no issues, however our radio was the KY97a ... I note that the Icom IC-A220 (plus MBA-3 adapter) swap suggestion states that it won't work with the KY96/97, has to be a KY96a/97a.
I hope that you've managed to sort it out.

Late response but this may help
https://www.sigtronics.com/_pdf/air_pdf ... ne_Mod.pdf

Mike is correct, If an external intercom is used it drops the ptt voltage ( only 0.7v )? .. so the fix is within the sygtronics mid linked above .. the ptt earth wiring is linked via a relay (also a diode as shown )..to provide a direct earth feed …
It is obviously a sensitive installation to the ptt earth so any problems in that area need resolved, or bypassed using the above (factory approved mod , by both sygtronics and icom ) I have correspondence from both .
Word of warning, it’s not just plug and play .. compare old and new wire / plug locations.. main feed wire needs moved and a second wire ..my install works perfectly..