14 April 2024

MARS Modding the IC-705

Yesterday I decided it was time to do the MARS mod - wide-band  HF transmit modification - to my IC-705. There was nothing special about yesterday, other than the fact that I finally screwed up the courage to open up the little radio and git 'er done!

I like to do the MARS mod on as many of my HF radios as possible. I'm a MARS and SHARES operator, and doing the mod gives me the knowledge that I can use this very expensive and capable radio outside of the ham bands. I've done MARS mods on the IC-7100, 7200 and 7300, Yaesu FT-891, the 991 and the Elecraft KX2. The process differs from manufacturer to manufacturer. Icom's process is the most destructive - you have to carefully remove very small diode(s) from one of the boards in the radio. Yaesu's is the least destructive - you create a solder bridge across one or more open pads on one of the boards. Elecraft's is the most elegant - you simply do a firmware update. 

There are several good on-line resources for IC-705 mod. Of course you won't find anything official from Icom on the subject, but it doesn't take long for the info for any radio, from any reputable manufacturer, leak out. So it was with the IC-705. Within a few months of release, word was already circulating on how to do the modification.

Before going further, I need to say this - if  you want a MARS modified radio your best and safest bet is to buy a new one from the major distributors like HRO or GigaParts. They are authorized by the manufacturers to do the mods, have all the technical data, equipment and experienced personnel to do the job, and your radio retains the original manufacturers warranty. Yes, you'll pay extra, but it is the safest route to take if you want a new ham radio with this modification. I only do this mod on radios that are out of warranty, and I do it only on radios I own - I don't do this as a service for others. 

OK, back to the resources. There are several videos on YouTube showing how to do the mod. All follow the same steps, but in each the mod is done with varying levels of expertise. In one or two I'm surprised the radio survived the surgery. The best video I've found, and the one I watched several times before doing my mod, is the one put together by TRX Lab:

There are also modification instruction sheets posted to the mods.dk website. Mods.dk is a paid subscription website, but they do allow the download of one document per day to those who are not paid members. If you go there, look for the document dated 26 March 2023.

The mod involves removing one very, very small surface mount diode from a portion of the main board that is very crowded. This implies finesse, and the right tools. Of course you'll need heat. Most use a soldering iron. However, I've invested in a quality hot air station specifically designed for electronics use. The model I bought is the Quick 861DW. The Quick is considered a basic 'pro' unit, but it gets generally excellent reviews from people I trust. Honestly, I don't even look at my soldering iron when doing this kind of work. The hot air station is a much better tool.

All the other tools are pretty run-of-the-mill for electronics hobbyists:

  • screwdrivers (I use JIS standard screwdrivers when working on Japanese manufactured gear)
  • forceps and tweezers 
  • heat resistant tape (for masking components on the board)
  • static-safe prying and opening tools (commonly called spudgers)
  • wrist grounding strap
  • static free work surface
Magnification is your best friend. I don't care how good your eyesight it, unless you are the Six Million Dollar Man with bionic vision, you are going to need lots of magnification. The diode that needs to be removed is about the size of a speck of ground pepper! I use a combination of a swing-arm LED lamp with a built-in magnifier and an OptiVisor headband magnifier with a separate magnifying loupe and LED illumination. Often it requires using all of these in conjunction to properly see the board components I'm working on

So let's get to the radio. The radio comes apart like a bit of a puzzle box, but overall it's not too bad. Honestly, one of the biggest pains was getting the six screws out that hold the two halves of the radio together. Everything is tight, and two of the screws are, I suspect, set with thread locking compound. They were a PITA to get out, even with the correct JIS screwdriver, and I buggered a few of them up. But once the radio is open, it's pretty straight forward. You have to remove the front panel and the two connecting ribbons, the sheet metal RF shield and another smaller ribbon connector (at the bottom in the photo below). There are two small antenna cables to disconnect. Once everything is unscrewed and disconnected, wiggle the main board out and rotate it so the bottom of the board is facing up. 

The front panel removed and flipped face down (note the speaker in the lower left corner of the panel).
The main board is underneath the RF shield. It has to be removed and flipped over to
access the diode that needs to be removed. This requires disconnecting the two large ribbon cables,
the smaller ribbon cable at the bottom, the RF shield, and then disconnecting two small antenna
cables (underneath the shield). After that the main board can be removed and flipped over

Here are the two black and gray antenna wires on the main board that have to be removed before the main board can be taken out and flipped over. One is the HF connection, the other is the VHF/UHF connection. Not sure which is which.

Here's the main board removed and flipped over. The diode to be removed is in that 'field' of diodes at the bottom center of the board (outlined in yellow). Luckily the diode in a good location at the bottom left corner of the field. (Sorry for the fuzzy quality of the image, I think the camera was stuck on macro mode.)

According to the instructions downloaded from mods.dk, on US versions of the IC-705 only the diode in the lower left corner needs to be removed (circled in yellow below). Other sources say a diode on the second row also needs to be removed (circled in white). However, this diode seems to be related to 60 meter capability, and since the US version of the 705 already has 60 meter capability (enabled in firmware?), I decided to leave it in place. If future testing reveals this second diode does need to come out, I'll tackle that later.

The next step is to apply heat resistant (Kapton) tape to mask out just the diode that needs to be removed (circled in yellow, below), and protect surrounding components. It's even important to mask open component pads, to avoid melting the solder on the pads and accidentally creating a solder bridge.

Next comes the steady hands part. Apply heat from the hot air station to the diode for just a few seconds, grab it with a set of tweezers, and it should lift right off the board, leaving an open pad that doesn't need any clean-up. Some sources say you should add extra lead solder and flux to each end of the diode pad, to lower the melt temperature of the lead-free solder Icom uses when it builds the boards, but I don't find that necessary if I properly mask out the component using the heat resistant tape. 

Gone, gone, gone...

Once the diode is off the board and you've checked the pad to make sure everything is clean, the only thing left to do is put it all back together and test. The 705 goes back together in reverse order, with a little wiggling to make sure all the ribbon cables are routed properly.

Once that's done, test on various ham and non-ham frequencies (into a dummy load, of course) to ensure the radio does in fact transmit outside of the ham bands and at the correct power levels. Everything looks good!

In all, the process was easier than I thought it would be. The little rig really isn't that hard to open up and navigate around in. Just take the usual precautions - use an anti-static wrist band, work on an anti-static work surface, use the appropriate tools, and you should be all right. Oh, and take lots of pictures to document your process in case you forget what board, ribbon cable or screw goes where.

The radio is a very neat, trim and compact design on the inside. Hey, it's an Icom, right? It's also a very rugged build; everything inside the case is very well secured - literally screwed down tight. There's no wasted space and nothing is flopping around in there. It's a brick. Honestly, with everything so tightly packed in and with no airflow it's a wonder these radios run as cool as they do. 

So that's it! If you have any questions or comments please post them below or contact me at w8byh@arrl.net, and I'll be happy to respond.

W8BYH out

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