[Icom] IC-706mkII problem---RESOLVED!

Sun, 21 Jul 2002 11:24:27 -0500

Thanks for telling us William, I for one, was glad to read the whole story. We
all need a refresher in troubleshooting form time to time and a lot better to
get it second hand than in person!

KC5GNB

"William J. Wickstrom" wrote:

> 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
> [email protected] <mailto:[email protected]> ; [email protected] <mailto:[email protected]>
>
> William J. Wickstrom, Chief Engineer,
> Surge Performance Sound.
> [email protected] <mailto:[email protected]>
>
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