Path: rrze.uni-erlangen.de!fauern!zib-berlin.de!Germany.EU.net!EU.net!news.kreonet.re.kr!overload.lbl.gov!agate!nntp-ucb.barrnet.net!autodesk.com!autodesk.com!olling 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