[TowerTalk] Or2800DC smoking control box

davidrobbins davidrobbins at ieee.org
Fri Jun 1 03:57:02 PDT 2012

The first thing to do is to see exactly which component lost it's magic
smoke.  That may give you some idea where to start looking.  As far as
measuring the wiring to the tower don't just check for the expected
resistances, check for unexpected ones also.  If the motor is supposed to be
floating(not grounded) then check it's resistance to ground.  Also check for
unwanted connections between motor and indicator circuits, I once had a
splice up the tower that had a strand of wire poke through the electrical
tape and short the indicator to the motor power, first time it turned the
indicator circuit died. 

-----Original Message-----
From: Nathaniel Lee [mailto:n1bnc at yahoo.com] 
Sent: Friday, June 01, 2012 00:08
To: towertalk at contesting.com
Subject: [TowerTalk] Or2800DC smoking control box

Hi All,

I am hoping for some help here with the DC rotor box from M2. The rotor and
box were installed brand new along with the rest of the installation and
worked fine at calibration on the dining room table and again for 2 days.
After which the rotor box smoked. I sent the box to M2 and it returned today
and smoked again upon wiring it in and I did not even have a chance to spin
the antenna before the magic smoke appeared. It also still smelled smoky
coming out of the shipping container.

Before doing so, I checked the wiring from the tower to confirm the motor
winding was not shorted and indeed, it had a few ohms of winding resistance.
The cable is not undersized for the distance either 200'. I actually tested
the rotor cable immediately after discovering the smoked box and it has not
varied in terms of the measurement of the motor wiring's resistance for the
last 3 weeks being without the box.

The M2 people are suggesting something is wrong at the tower level. Since it
cost a pretty darn big penny to have it all installed and I need a hip
replacement soon, I am not running up and down the tower for this. Someone
else has to go twice in order to retrieve and reinstall. $$! I checked the
tower ground which is tied into the station ground and upon separating the
two, the resistance was minimal, on the order of an ohm. 

They suggested checking the house wiring for a missing neutral? Really?
Nothing else is smoking and the tail-twister in use at another tower
performs flawlessly and is also tied into the same ground. Everything else
is just fine. Not even a hot chassis. I am using braid everywhere for inside
grounding and it goes to two 8' ground rods only about 5' away. 

How do I check for a missing neutral without getting zapped in the process?
What else can I look for? I am peeved that it worked for 2 days without
incident because it indicates it was not an installation error. Nothing has
had a chance to deteriorate. I suppose testing with a light on a 2 prong
plug would indicate a missing neutral?

Nat Lee

Somersworth, NH

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