The condition is often referred to as tin whiskers. There's a lot of info
about that on the web. NASA has done a lot of research about it. It's the
growth of tiny filaments mainly on tin-plated RF assemblies.
In the MSF5000, this condition can be found inside the two VCOs, inside the
mixer coil assembly, inside the RF front-end assembly, and inside the internal
filter/duplexer assembly. It usually happens on only the real shiny parts.
Motorola changed the alloy for their castings, possibly in the late 1980s, to
have a dull finish which is not supposed to suffer from this problem.
The VCOs and mixer coil assembly can be opened. The front end and duplexer
aren't supposed to be opened, but I don't know why. Maybe there are some
gaskets that must be positioned just-so. Way too many screws.
The adjusting cores can be removed and you can stick a piece of wood or plastic
through the hole, move it around, and see if that clears the whiskers out. It
doesn't take much. They will look like very thin cobwebs or hair-like strands
going between the inside of the assembly and anything else that just happens to
be near it.
I've only encountered it in the VCOs and mixer coil assembly. Disassemble the
unit, use a toothbrush or toothpick and move it all around the entire inside
perimeter. Wipe all metallic surfaces. Go around any coils or other components,
especially between them and the side surfaces of the assembly. Go into areas
you may not even see. This is about all you can do.
The growth seems to take years to occur. The filaments are extremely thin and
fragile and sometimes they'll break off or disintegrate if you just bang the
assembly on the workbench or lift it up a few inches and drop it.
Bob M.
==
--- On Mon, 5/4/09, Bob Luttrull kd7...@comcast.net wrote:
From: Bob Luttrull kd7...@comcast.net
Subject: [Repeater-Builder] MSF5000 440 UHF
To: Repeater-Builder@yahoogroups.com
Date: Monday, May 4, 2009, 11:23 PM
Hi all
I am having a problem with my repeater. It is a MSF5000 440
UHF 110W. I was told that it might have crystal hairs in the
TX duplexer. People are telling me that I need to
disassemble the duplexer and clean it with a toothbrush to
get the crystals out and use a nolock on the adjustment
screws. Is that right? If not can someone fill
me in on the correct way to do it and the right things to
use? I don't have a service manual for the unit but I
don't think I will have a problem.
Thanks
Bob
kd7ikz
