Icom IC-706mkII Fan Mod

My mobile rig is an Icom IC-706mkII HF/2m unit that’s been doing me well for months, semi-permanently installed in the car. Lately I’ve been noticing signs of its deterioration, getting signal reports that I’m either cutting out or the audio has a sporadic “electric shock” sound. I’ve been trying like hell to track it down, thinking my custom power cables were either sub-par, that my car’s electrical system (battery, alternator, regulator) were getting edgy, or that my final transistors were starting to fry. All of those options were scary to consider.

The symptoms exhibit more strongly when it’s hot outside and I’m chatting away on a local repeater on the afternoon commute. Eventually, the radio starts freaking out and I have to sign off.

As it turns out, my radio is overheating. The internal fan’s not doing its job.

I took it inside for examination. With the covers off, I put the radio on CW mode, half power, into a dummy load, and held down the key. The fan would only run while I had the key or PTT down, and never outside of that. Even when it was key-down, the fan took a long time to kick over; the driver circuit would attempt to start the fan, but didn’t have enough voltage to push the fan blades except after a few kickover attempts. So it never gets cooling if my talk times are less than 15 seconds (and the heat builds up over the QSO). I was afraid the fan was dying, but when I removed it and drove it with 12v, it blew like a champ (thankfully). So something is wrong with the fan-control thermal circuit.

I found a few references on various radio boards where others have had the same symptom on their own Icom IC-706mkII (and the mkIIg as well). Apparently, the original Icom IC-706 was designed so that the fan would blow constantly. When they designed the mkII and mkIIg, they added a fan circuit to limit the noise and current drain. Unfortunately, once that circuit gets marginal, it stops being useful and actually contributes to the radio’s demise.

Among the references is a rework involving the addition of a 200Ω 1W resistor between L50 and J2 (on the IC-706mkII, at least) which will provide a constant voltage to keep the fan moving at a slower speed. The benefit is that the fan controller won’t need to start the fan; it just ramps up to the right speed.

Two 100 ohm 1W resistors in series for 200 ohms (identified by screwdriver tip), wired between Vcc and the fan.

I soldered a pair of 100Ω in series and shrinkwrapped all connections so they don’t contact the radio circuit (I left the body of the resistors uncovered for cooling), then flew the rework over the board between solder points. It doesn’t appear to wobble or vibrate much, and there’s enough cooling inside that hot case to keep it from frying.

Orange wire (identified by screwdriver tip) soldered to coil L50.
Orange wire (identified by screwdriver tip) soldered to hot side of fan connector J2.

It’s been a week since the rework, and the radio’s still doing OK in the car. I’m still getting spurious reports of noise, but I think my radio’s got an EMI sensitivity when I drive near electric utility substations (EMI/RFI has always been a problem with my 706). But otherwise, it’s doing alright.

It sucks when we have to modify a production device due to engineering mistakes, but thankfully we have the public resources to help us find our way and stay on the air.

Year and a Day

Personally, I subscribe to the “one year and one day” concept in matters of learning a vocation, skill, belief, or hobby. During that period, a person is considered an initiate, a neophyte, a newbie. They may know a few things, but they’re only learning. They can’t be promoted to higher levels of trust during this lockout period; they have to pay with time and dedication. By no means are they to be considered a journeyman or a master of their class.

So January 20 came and went, and I forgot to write up a thing. January 20 is the one year anniversary of my first amateur radio grant, a Technician Class license (General Class upgrade came in April). I’ve been a ham for over a year and a day. I’ve gone through a heavy bit of learning by the books to shore up my knowledge and comprehension of radio communications, but the true learning comes by experience. I have to actually do the thing to know the thing, and this past year has been a lot of that.

I wish I knew more, did more, understood more, talked more, made more contacts. Even at my age, I feel like I still need to earn my stripes to gain some levels of respect in myself and from others. If I’m going to be talking the talk, I better be walking the walk. People ask me for advice, but more than half of it isn’t backed by any personal experience. Without experience, I’m just a blustery blunderbuss spouting off what I believe to be true. In the back of my mind, I can feel the real pros rolling their eyes when they listen in.

On my anniversary evening, I was asked to host the AARC ElmerNet because the usual host, Jeff N5MNW, was down with illness. I was glad for the privilege to do so, and thankful that he thought well enough of me to ask for a fill-in. I think it’s apropos that this happened on my year-and-a-day.

I’m no longer an initiate. I’m set loose from the nest to fly on my own. Learning is life-long.

So, from my QTH, to the F2 layer, and down to you all. 73.

Future Propagation

It’s massively unfortunate that amateur radio puts me in close proximity with doomsday conservatives and people who talk about zombie apocalypses as if movies were real. They talk as if knowing how to use a radio is a vital survival skill, right up there with firearms, hunting, and shelter.

When unlicensed people talk to me in the park while I’m operating, chances are that at some point they’ll mention the end times. Even some of my friends say, “when they come for all of us, you’ll be allowed in my bunker because you know radio.” They laugh, I oblige, but deep down, i still bristle at the connotation.

Believe it or not, I’m not so fatalistic. I like radio for its technical, atmospheric, and super-national communications aspects. It’s a series of puzzles to solve, not a preparation for the end of days. I raised myself up in a religion that continually talked about the end times, about Armageddon, about rapture, and fervently prayed that the end would come to fruition in our lifetime (can you believe that?). So I’ve had my fill of that talk. No thanks.

I’m in the hobby for the pure pursuit of the hobby. Why does everyone see it differently?

Palabra Jot

I’m thinking I need to sign up for some sort of creative writing class. I mean, sure, I like to write, and I think I’m fine at it, but I want to be more together with it, more regular, more devoted, more productive. Y’know? Something to knock me out of my doldrums.

See, I don’t do well when left to my own devices. I need a regimen, a schedule, a habit, a hobby. Y’know? So if I was in a class, or a writing group, I’d be more with-it. Seems the only time I write creatively is to rise to the challenge. My previous short, “To Dust“, was  written for an anthology I was invited to join; I had a deadline. I finished the first draft in a hard week or writing, finished the second and final drafts the next week. I rose to that challenge and wrote a good piece.

But that was over a year ago. I haven’t written anything since. I need motivation; I need a pitchfork in my back. Y’know?

The Austin Library has a Write Club class that meets every month for a few hours; thinking about joining along, see what’s up. Can’t hurt, right? I need to get more involved my hobby. Something. Something.

C Is for ANSI, That’s Good Enough for Me

In a bid to expiate myself, I’m currently reading “The C Programming Language, Second Edition.” Written by Brian Kernighan and Dennis Richie, the inventors of the language, this book is the bible when it comes to learning the language. Most modern languages owe their existence to this one. All modern operating systems are primarily written in C. Most client applications are written with C’s direct descendants. Since I work at a high technology company, it would behoove me to bother trying to learn it again. Most of the high-level languages I’ve used in the past 2 decades cannot match the speed, specificity, and hardware-level capability of C. But these aren’t reasons enough for me to learn it.

When I say “expiate”, I mean to make amends for failing a semester of C in college. In a class of 3 students, it was difficult to stand alongside my classmates and lean on them for support. When they started excelling, I fell behind and somewhere around a month after learning about pointers and indirect references, I just gave up. I swore I’d never bother learning the language again. But that’s all changed now. I could do well if I could wrap my head around it and succeed where I failed before.

What bothers me is I still have a lack of support from my fellow programmers. Even the guys who I thought would support my decision to take up the language again are saying things like, “Man, why are you messing around with C?” or “You must really want to punish yourself.” I say they’re missing the point. I’ve had my time with the high-level languages. I know that I can split a sentence into an array of words in three lines in Perl; I know that doing the same in C would require a bit of memory allocation, a handful of variable declarations, and a set of functions to perform each bit of the search and copy operation. But you know what? I don’t care. I’m getting thrilled with seeing how it all actually happens under the covers of all the other languages.

I want to succeed in this. I want to use C to make stuff that runs fast. I want the chance to flip bits in hardware without needing special libraries. I want to have a shallow learning curve if I decide to go into microcontroller programming. Some people put puzzles together; I have this.