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Re: [TowerTalk] stuck US towers 472MDP solution

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] stuck US towers 472MDP solution
From: John Farber <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Wed, 07 Apr 2010 20:01:10 -0700
List-post: <">>
I had a stuck US towers motorized 472MDP, 72 foot motorized tower, with 
the remote control RM-1000 unit. The symptoms were on the remote control 
box in the shack, the lights for up and fully up were on as well as both 
lights for fully down and down were on and the tower would  not move up 
or down, either from the shack or from using the remote switch at the 
base of the tower.We were in the middle of our stormy season here on the 
West Coast,
and I wasn't comfortable leaving the tower fully extended with a high 
gusty winds we were experiencing. Over a couple of phone calls to US 
towers I was told to remove power to the control box on the base of the 
tower fabricatees and jumpers
install a jumpers power up the tower and lower it. Unfortunately I 
didn't really get a break in the weather for weeks, and felt 
uncomfortable working on a tower when there was this high probability of 
lightning. So I left the tower fully extended, and took a different 
route. I've posted my problem to the tower reflector, and got several 
suggestions but  one of them really hit home. Someone suggested that the 
limit switches were notorious for getting water in them. So the first 
clear day I investigated and found sure enough there were signs of water 
in my lower limit switch. I copied the numbers off the limit switch, an 
Alan-Bradley 802T, AP, series H. unit. I then set about trying to locate 
one.  I found they had a retail value of something like $175 ouch! So I 
tried eBay, for the first time and wound up buying one new  switch and 
one used switch just to have a backup. It turns out that the switches 
have a clam shell design. Upon opening the switch there is a smaller 
black plastic unit which is actually a microswitch with spade connectors 
on it. These Alan Bradley switches are described as plug type. The 
actual part that had failed was the small black plastic microswitch unit 
inside the much larger two-part outer shell. Today I tackled the fix for 
this unit, and wound up splitting apart the clam shell on the old 
switch, and swapping out the black plastic microswitch inside. This 
approach saved me from having to deal with unhooking the wires into the 
clam shell and dealing with the other waterproof cable clamp on the 
bottom of the clam shell. The change out took me perhaps 10 minutes, and 
the most difficult part was getting a reluctant screw out without 
stripping it. Upon checking the tower function after doing the 
replacement all is well. So in conclusion, I didn't have to make up any 
jumpers or mess around with the relay box at the base of the tower and I 
didn't even have to change out the whole limit switch-only that small 
black plastic microswitch inside the outer housing. By the way I was 
able to find a replacement limit switch for $30 on eBay. I hope this 
information helps anyone in the same situation. 73, John Farber, KG6I


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