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[CQ-Contest] Dissected/ Autopsy Hofi coax Switch

Subject: [CQ-Contest] Dissected/ Autopsy Hofi coax Switch
From: jreid@aloha.net (Jim Reid)
Date: Wed Apr 8 10:58:50 1998

Aloha,  Thanks to the many who replied with comments about
this coax switch.

The problem of opening was finally solved by brute force:  the
knob just had to be forced off the shaft after two set screws
were removed.

Just under the top cover,  which comes off after six screws are 
removed, is the detent mechanism.  The solid shaft to the knob
ends here.  Beneath the detent device,   a small nylon (?) rectangular
"shaft" extends down below to turn the wiper arm of the actual

The  failure of this particular switch began with the loosening
of two small screws which hold the detent device to an inner top
mounting plate beneath the top cover.  Evidently with use/vibration,
somehow both these screws came loose.  This allows the detent 
mechanism to wobble;  if the wobbling is large enough in arc,  the
nylon shaft can break:  it did in my switch!  I had not even noticed this
small shaft wobble of the knob.  The small nylon piece is actually
bolted with a thru screw to a small extension beneath the detent
gadget -- talk about complicated construction  This begins to approach
pocket-watch mechanism technology!  The break occurred exactly at
the bottom of the small machined piece below the detent assembly
thru which the small retaining bolt passes via  a small hole
drilled across the rectangular nylon drive shaft;  an obvious point
of failure caused by the wobble allowed when the internal
detent mounting screws loosened.

The fix is to obtain a new nylon drive piece from Germany;  not
sure it is worth the hassle to attempt to obtain same. Will
order an Alpna Delta from HRO!

73, Jim, KH7M

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