In past posts I've hinted that I'm not afraid to get into the gust of certain radios to do what is referred to as the 'Mars mod'; open the radio up for wide band transmit for use on MARS and SHARES frequencies. To date I've done it on two Icom IC-7100's, two Yaesu FT-891s and, before I got adventurous with a soldering iron, paid to have it done on an Icom IC-7200, a 7300 and a Yaesu FT-991A.
A week ago, as part of my pure fleet initiative, I bought a used IC-7300 from a seller on QRZ.com. I've been haunting various ham radio equipment sale and swap sites for a while now, looking for a good deal on a used 7300, so when this one popped up I grabbed it. Even before I had it in-hand, I was thinking about doing the MARS mod myself. The modification procedures for many HF rigs are available on the internet, and for modern Icom radios it usually means removing a diode from the main board to open up the transmit stage (opening up the receive side is usually not necessary). In the past I used a soldering iron to loosen the solder holding the surface mount diode to the board, and that's a worrisome mix of shaky hands, teeny-tiny closely packed components and a hot soldering iron. But as I was discussing this process a few days ago with my good friend Ken, AI4UW, he asked two key questions: Do you intend to ever re-install the diode? Is the diode in a location you can get to it with a pair of miniature side-cutters? No to the first, yes to the second. Well, he said, just go in with a small set of side cutters and snip it off the board. Just make damned sure you snip the right diode! Ken does high level aviation electronic system repair for Delta Airlines. If you fly Delta into or out of Atlanta, odds are good that Ken has worked on an electronics system on that plane. He knows what he's talking about, so I decided to follow his advice and go the 'snip' route.
|The diode we're after is on the underside of the main board, so we have to|
remove the bottom cover
|We're after diode D422, and ONLY D422|
|It's important to have your references at-hand when doing this work. The last|
thing you want to do is remove the wrong component
|You're gonna' need magnification. Lots of it.|
|It was hard to get the camera to focus, but the diode is about where the arrow is pointing|
|Again, poor focus, but you can see the pad for the diode after it was removed by snipping it out|
|Glamour shot! Here's a wider view of the radio from the bottom, looking at the underside of the|
main board and the build-in tuner. The IC-7300 is actually a very beefy radio