N2MH Information for Mobiles

IC-706 MKiiG Problems

Sick Radio

This note is about some problems that I found in my IC-706 MKiiG mobile radio and how I fixed them. If you have this same radio, you may or may not find these same problems. Your Mileage May Vary (YMMV).

The other day I went to run Essex County, NJ as part of my County Hunting activities and had to abort the run when the rig would not key on CW. Going home, I pulled the rig out of the car and put it on the bench. I found three things wrong with the radio, fixed them up and now the radio works right.

Before the show-stopper in Essex, there were three things that were annoying about the radio. None of them were serious enough to pull the radio and put it on the bench. But, they were indications that something wasn't right. They were:

The Fix

CW Keying Problem

The first thing I did was to fix the key jack. The two ground connections on the jack were completely loose. They no longer made connection with the pc board ground. Thus, the ground never made it out to the paddle.

This was an easy fix - I simply resoldered the two lugs and put a substantial amount of solder on them. While I was at it, I also resoldered the other two connections - the ones for the dot and dash lines (again, with a little more solder). This fixed up the CW keying problem.

HF Flutter Problem

While I had the radio open, I took a look around to generally take a look at the radio. In the transmitter power amplifier section, I found a small toroid transformer held in mid-air by two of its solid, bare leads. The other two leads were thin, stranded, and were not supports for the toroid. Looking closely, one of the solid wires from the toroid was very close to one of the connections to a power transistor. I found that the toriod would bounce a little bit on its support leads. It looked like the lead near the power transistor would actually make contact with it when it bounced. In additon, it seemed to bounce at the same rate as the flutter I was noticing.

I didn't like this close proximity, so I bent both leads of this toroid up and away from the pc board (and thus the power transistor). I bent them enough so that when the toriod bounces, it no longer would be close to the power transistor. I was really surprised that Icom did not put any sleeving around those bare leads or use insulated wire.

VHF/UHF Spurs/Birdies

I've seen spurs/birdies on VHF and UHF before and the cause of that is generally poor grounding or shielding. So, looking at the insides of the radio, I did not see any obvious faults with the shielding. However, I did notice that several of the pc board mounting screws were a little loose. So, I went ahead and tightened all of them for good measure. I did not do any of the screws holding the power transistors as I'm not sure if they actually go to the chassis. I'm also not sure if there is some requirement that those screws be torqued when they are tightened.

I also found that the screws holding the two coax connectors on the back panel were a little loose. To be complete, I tightened them also.

Results

After I buttoned up the radio and put it back in the car, I'm happy to report that the rig now keys FB on CW. In additon, it does not seem to have the flutter on HF. And, VHF and UHF seem to be back to normal - the spurs/birdies are now gone.

I'm happy that this is all it took to fix this radio. It also points up the fact that the mobile environment is quite different from the base station environment. A car is a source of a considerable amount of vibration and its bad effects. Thus, one has to keep an eye on things and do a little preventative maintenance once in a while.


This page last revised on December 13th, 2007.
N2MH Email Address