[ICOM] FIXED IT!: IC-756ProII CI-V DEAD!

[William J. Wickstrom]

FIXED IT!

Working great now!

A special “thank you” to Larry, K4LXV for some tips that made this
troubleshooting job much easier.

Oh, and by the way, Mouser had all the parts in stock, and shipped to my
location in < 36 hours!

On to the next crisis…

William J. (Jim) Wickstrom, W1IK
Technical Director,
Utica/Shelby Emergency Communication Association (USECA)
w1ik at arrl.net
www.usecaarc.com 


________________________________________

Ok Gang:

I found two (2) affected components on the Main Board:
* W701, 0.0Ω SMD resistor (jumper) on bottom of Main-A board (connects
sleeve of CI-V jack to chassis ground), OPEN
* Q3772, 2SC4081 NPN SMD BJT (CI-V Tx driver) on top of Main-A board,
LEAKING B-C

As long as I’m in there, I have decided to also replace:
* Q3771, 2SA1576A PNP SMD BJT (CI-V Rx driver) and 
* IC3771, TC7W04FU SMD C²MOS Tri inverting buffer IC (CI-V buffer amps)

Both of these are also on the top side of Main-A board. Being that the
parts were WAY cheaper than shipping, I got two spares of each component,
just to cover the “oops factor” of dropping them into the abyss that is
my workshop floor! =-O

I'll let you know if this solves the problem.

73

William J. (Jim) Wickstrom, W1IK
Technical Director,
Utica/Shelby Emergency Communication Association (USECA)
w1ik at arrl.net
www.usecaarc.com 

-----Original Message-----
From: William J. Wickstrom <jwickstrom at surgesound.com>
Subject: [ICOM] IC-756ProII CI-V DEAD!
To: icom at mailman.qth.net
Date: Tuesday, January 1, 2013, 4:19 PM

Hello, All:

While operating SKN last night the CI-V data to/from my 'ProII quit (it was
working fine, and all works with my 'mkIIG). I have been able to determine
that the problem is indeed within the 'ProII, and NOT anywhere else in the
CI-V chain. I believe that perhaps some stray RF, or perhaps some other
spike, took out the CI-V in the 'ProII. I have the service manual (in .pdf
format), but could use some guidance as to where to start looking for
faults. Has anyone else had this kind of problem occur? Any help from this
group would be greatly appreciated!

-----------------------------
Date: Tue, 1 Jan 2013 14:46:26 -0800 (PST)
From: Larry Young <k4lxv at bellsouth.net>
To: ICOM Reflector <icom at mailman.qth.net>
Subject: Re: [ICOM] IC-756ProII CI-V DEAD!
Message-ID:
	<1357080386.76663.YahooMailClassic at web181006.mail.ne1.yahoo.com>
Content-Type: text/plain; charset=us-ascii

Bill: Here is a CI-V port test for the ProIII courtesy of John K3CT of the
ProIII Yahoo group:

1. Disconnect the power from the radio and insert a blank 1/8" plug into the
remote (CI-V) jack.

2. Measure the resistance from the plug shield to the radio frame. It should
measure less than ~1 Ohms. If it is open or resistive, replace the TDK
ferrite bead on the back of the radio board.

3. Using the blank 1/8" plug again, measure the resistance from tip to
shield. It should measure high resistance (>400 K Ohms) if not, Q3772 is
likely damaged.

4. For those that don't have the computer case and radio both connected to
ground, consider adding the connections so the computer and radio stay at
the same potential during lightning or surge events.

I suspect the ProII and ProIII CI-V circuits are the same. The Q3772 number
may be different.
Good luck,
Larry K4LXV