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From: olling@autodesk.com (Cliff Olling)
Newsgroups: rec.radio.amateur.equipment
Subject: Kenwood TH-79A loose antenna connector repair
Date: 7 Feb 1995 02:37:54 GMT
Organization: Autodesk, Inc.
Lines: 75
Message-ID: <3h6me2$7qu@autodesk.autodesk.com>
NNTP-Posting-Host: zatsuyoo.autodesk.com

Caveat/disclaimer:  Don't blame me if you wreck your radio or void your
warranty attempting any of this :-).

The combination of people on the radio telling me I was scratchier than
usual and my noticing that my antenna was wobbling around inspired me to try
to tighten up the antenna connector (BNC).  Here's what I found...

I opened up the two halves of the case, as described in all the mod docs.
Note that the screw under the mike/speaker jack cover is different from the
others, and may require a different screwdriver (with thinner "blades").
Also note that there is a tongue-and-groove arrangement on both sides of
the battery compartment that you'll need to pop open gently.  As explained
below, *don't* attempt to slide the two halves of the case apart to open
it up.

Upon opening the case into its two halves, I found that the BNC is _not_
attached to the same half of the case that the circuit board is attached
to, leading to the weirdness that I found below.

I found that there is a heavily tinned wire coming out of the BNC which has
a right angle in it.  It doesn't appear to be flexible at all, which is
good, as you'll see below.

The weird thing is that the other end of this wire isn't soldered to the
circuit board.  If it was, you wouldn't be able to open the case without
breaking the wire off of the circuit board :-(.  Instead, apparently the
wire just rests against a tiny(!) contact pad on the circuit board.  Very(!)
near to the contact pad is a equally tiny surface mount device of some kind,
and the legs of an IC.

So imagine that you've got this (enormous, relatively speaking) wire finger
sticking out and down from the back of the BNC connector, leading down to
touch the surface of the circuit board, just between the tiny surface mount
device and the IC legs.  If that wire finger was able to wiggle the least
little bit (we're talking <2mm here), it would intermittently short to
either the neighboring surface mount device or to one of the IC's legs,
rather than connect to the tiny contact pad that it's supposed to be
touching :-(.

And the bad news is, if you let it get bad enough, this is exactly what
happens when the antenna connector comes loose :-( :-( :-(.  So hopefully now
you'll be interested in reading about my experience in tightening it up :-).

Ok, so you've gingerly opened the case, and find the two halves are
connected by a ribbon cable and 3 wires that are tied together.  There's not
quite enough slack in the cables to lay the halves of the case flat, so be
careful you don't accidentally rip them out by the roots :-(.

You'll be able to see the bottoms (threads) of the two screws that hold down
the antenna connector, but the heads are under a piece of plastic that
surrounds the antenna connector and wraps around the top/back of the radio.

To remove this plastic, first remove the antenna from the radio, and throw
it in the trash can (just kidding) :-).  You'll see that the plastic is held
down by a thin piece of foam rubber that's stuck to it and to one of the
metal RF shields.  Very gently peel the foam rubber off the plastic piece
you're trying to remove.  It's really easy to tear it, so work slowly.  

Once you've got the foam rubber off, you can wiggle the plastic piece off,
but you'll find that you need to remove the rubber O-ring from around the
antenna connector first.  Do that, then the plastic piece should come off
easily, exposing the screws that need to be tightened.  

Once you tighten the antenna connector screws, just reverse your procedure,
and hopefully your radio will still work :-).  Caveat:  Remember the "wire
finger" sticking out of the back of the antenna connector?  Make d*mn sure
that when you put the two halves of the case back together that you get them
lined up perfectly (<2mm slop, remember?) before you try to do the final
closure.  Otherwise you risk getting that wire finger hung up on that tiny
surface mount component or the IC's legs that I wrote about above.

Have fun, and let me know how it goes,
--
Cliff Olling  Autodesk, Inc.
olling@autodesk.com