[ForSale-Swap] IC-706mkII problem---RESOLVED!

[William J. Wickstrom]

Hello, All:

            First, let me just say thanks to all of you who responded to my
original posting. This reflector is an invaluable resource for anyone who
has ever owned, does own , plans to own or is trying to decide about owning
any piece of Icom equipment. I’m a big fan.

            Now, lets recap the original posting:

“Hello All:
            I just love my ‘mkII, but it just today developed it’s first
(ever!) problem, and it’s got me scratching my head:
I was in the middle of a QSO (mobile) with a friend on a local two-meter
repeater, and when I unkeyed the mic, I noticed the radio had gone dead (no
display, no lights, no audio). Checked the power connections and fuses, and
all was right there—but then I noticed that the radio now emits a mechanical
clicking from an internal relay, cycling at about 2hz (“Tic-tic-tic-tic
”)
whenever the rig is connected to power. The power switch has no effect, nor
does powering the rig from my shack supply (which is currently running the
‘ProII just fine). Just the same relay clicking.
            I have removed and reseated all connections to the radio,
including the front control head to the radio—no change. I don’t have a
service manual (yet) and, short of just tearing into it blind or sending it
off to somewhere (probably Malcom), I’m at a loss. Any ideas? Anything I
might have missed?”

      Now, here’s what I found:

I was all ready and resolved to send the radio off to Washington state
(Malcom Technical Support), when I decided to do “one last test”---I swapped
the power cable out with the cable that powers my ‘ProII. Bingo! The radio
powered up and operated perfectly. Ok, we eliminated the radio itself as
defective (whew!). But what could be wrong with the ‘706’s power cable to
make the radio behave the way it did? Off to the bench for closer
examination.

I applied DC power (14.5 volts measured with my DVM at the supply) to the
input side of the cable and checked the voltage at the radio connector (the
only load being the meter itself)---14.5 volts! “What’s going on here?!”
Ok, let’s put the radio on the cable and see if it “fixed itself”.
“Tic-tic-tic-tic
”, same problem (well, of course, we didn’t fix anything)!
Let’s check the voltage at the supply again---14.5.
How about at the input side of the fuses?---14.5.
At the output side of the fuses?---Ah-HA! 5 volts! Ok, NOW what’s going on?
We’ll disconnect the radio. Now 14.5 volts at the output of the fuses!
Apparently there’s a high (relatively) resistance in the path somewhere
(remember Ohm’s law?), we’ve gotta be close.
But wait---don’t fuses OPEN when they go bad?
Let’s pull the negative fuse out and check it out---LOOKS ok. The continuity
beeper function of the meter SAYS it’s ok.
How about the positive fuse?---LOOKS ok. The continuity beeper beeps.
“Hmmmm
something’s weird here”
Let’s go to the ohms x 1 scale just for the heck
..FIVE OHMS?! Double AH-HA!
Digging into the solder on the end caps of the fuse with my meter prods
dropped the ohmic resistance to nil. Well, well, well. The solder on these
factory fuses must be failing (oxidizing) after some four years of
trouble-free service!
No problem---we’ll just put in some new fuses. Darn! No thirty amp fuses in
stock in the workshop.
I know, I’ll reheat and flow some new solder on the end caps of both fuses
(just to be sure).
It WORKS! Well, at least for now. Gotta get some new fuses in there, or
pretty soon---“Tic-tic-tic-tic
”

 So now you’re all thinking “Ok, it’s a nice story, Jim. Why are you wasting
our time with it?”

Well, after working as a professional audio engineer for some 18 years, and
playing around with radio and electronics most of my life, I’ve learned a
few common sense things about troubleshooting. I know when a fuse is bad,
don’t I?
My “I already checked everything” attitude almost cost me a big chunk of
time without my beloved ‘mkII, not to mention the cost of shipping to and
from Washington and a bench fee just for Scott Malcom to replace my fuses!
And think of the embarrassment! I’d just HAVE to lie about it for the rest
of my life! “Oh yeah, It was really screwed up”. Crisis averted---thanks to
putting ego aside and taking a thorough and measured approach  to
troubleshooting (remember high school electronics class?).

Thanks again for the help, and for putting up with my tediously long
anecdote.

William J. (Jim) Wickstrom, W1IK, NNN0AHC
USECA Morse Instruction Coordinator
w1ik at arrl.net <mailto:w1ik at arrl.net> ; w1ik at k8uo.com <mailto:w1ik at k8uo.com>

William J. Wickstrom, Chief Engineer,
Surge Performance Sound.
surgesound at ameritech.net <mailto:surgesound at ameritech.net>