Don't take that antenna down just yet. It is much more likely that the
problem is on the ground.
First some basic operational details that may help you understand
possible causes. Maybe if I give you enough information you will think
of something that you didn't describe and didn't think about as being
the problem. This is kinda long, but maybe it will be useful. You
probably don't need to know all this, but I don't know which part you do
It is true that the motors are current driven, and this current
regulation will work correctly provided there are no shorts on any of
the control wires. (It may work correctly if the short is only across a
motor winding.) There is no current limiting or any other control
mechanism to save a driver IC should there be a short of one of the
control lines to ground or to any other line. Without the controller to
radio serial cable there is no direct connection between power supply DC
ground and the case, however excessive current can be pulled going thru
the capacitance inside the power supply (about 15 nf between AC ground
and DC ground) should an output line be shorted to ground. With this
serial cable there is a direct connection between DC ground and earth
ground so blowing the driver is much easier. A faulty surge suppressor
can also be a problem. Usually what happens when there is a short of
any kind, the driver IC will blow, and the control box will go off. If
the box was on when this happened, the box will go off and may then come
back on. If the short occurred while the box was off, when turning the
box on, the LEDs will blink one time and the box will shut down. The
control box can be made to come back on, but there will no longer be any
control of the element that has the problem. Other elements may
continue to function.
A DC voltage applied by a ground loop in the system should have no
effect on the controller if there are no improper loads on the control
lines out to the antenna. However if you have a transient suppressor in
the system and that loop voltage becomes high enough to break down the
transient suppressor, then it may damage the driver because then the
driver can dump excessive current thru the transient suppressor (kinda
The box shutting down is usually the result of power supply overload,
causing the voltage to drop to a level which makes the control box
electronics malfunction. You should have a 33 volt power supply. If
that overload is a result of an improper load on one of the output
lines, you can bet that the box now has a dead driver IC. This load on
the supply is usually removed when the driver IC blows (so it shouldn't
shut down again), however I wouldn't rule this out entirely. It is
possible that the driver IC failed in a shorted state and did not burn
up traces inside the IC which is more common. The shut down could also
be the result of a bad power supply in which case the driver IC may
still be good.
A cable that is too long or has a too high resistance should not cause
the controller to shut down. If the cable is long enough to drop enough
voltage such that the driver IC that does the current regulation has no
headroom left, and therefore cannot produce current regulation, the
element may not move to the proper position. If the length is marginal,
it might be intermittent, sometimes moving to the right position, or
maybe close. Settings may not be repeatable. This can cause some real
head scratching. This should not cause the control box to shut down.
A similar condition can result if there is too much capacitance on the
control lines, such as may happen when someone uses a surge suppressor
that also contains a bypass cap. The current is regulated dynamically
by the IC. It pulses the lines by shorting them to the supply, measures
the differential current being drawn, and then opens the connection when
a preset current limit is exceeded. This is done a relatively fast rate
(I forget the frequency). The IC is expecting this current to gradually
ramp up as it should do when driving an inductor. If there is a cap on
the line, the current will rise very quickly causing the driver to turn
off, leaving the motor winding with not enough drive current. This will
cause the element not to go to the correct position, or it may only go
part way to the correct position. An MOV that has too low of a rating
or is shorted (even temporarily) will blow the driver IC.
Now that you know a little more about how it works, maybe this will help
in diagnosing the problem. Now a few suggestions.
1. When you say that the addition of the fourth element "killed" the
antenna, do you mean it didn't work properly, or the controller box shut
down? If the control box is shutting down, then the problem can be
either the power supply or the controller. Since you have replaced the
power supply that leaves the controller. A one-time shut down of the
controller usually indicates a controller driver IC failure due to a
control line short, but a repeated shut down can indicate some other
problem inside the controller. The reason for this may become more
obvious after you read the other info below.
2. Disconnect the control box and do an ohmmeter test of all the
control lines to make sure there is an open circuit between all control
lines and ground, and check for an open between each line and ALL OTHER
lines except for the mate for that line.
3. Remove any surge suppressors or other devices you have attached to
the control lines.
4. You can check to see if elements are moving by going to the
Create/Modify menu and moving only one element at a time and observing
that the SWR changes when each element moves. The second director
should only cause a small movement in SWR, but any change at all
indicates that the element is moving.
5. If you have an oscilloscope, you can verify that the control box is
still working. Disconnect the control cable. Each motor is driven with
only two wires. Locate the pair used for the element you suspect may
have a problem. Put a load on the back of the control box on the lines
to be tested. Don't use the full load like the resistance of a motor
(it will get hot), all you need is something like 1K ohm between the two
lines. With the scope, measure the differential voltage on these
lines. You will see some funny looking waveforms with a peak amplitude
of twice the supply voltage. (The driver IC automatically switches the
polarity on the two lines, so the voltage measured differentially will
be twice the supply. ) If you don't have a scope, you can do a primitive
test with an AC voltmeter and measure the AC voltage on these lines and
compare what you get to other line pairs. If it is significantly
different, then it is likely that the driver IC is bad. It will be hard
to measure with a voltmeter because the average value changes a lot when
you switch bands (peak values are constant). If it doesn't change then
you know the driver is definitely bad. CAUTION: DO NOT LET THESE LINES
SHORT TO THE CASE. It will blow a driver IC! And don't connect the
scope ground lead to either of these lines, connect the scope ground to
the controller case. You need two probes.
If you sent the original control box back to SteppIR, maybe you could
call them and ask if the returned box was good or had a bad driver IC.
If it had a bad driver IC, chances are that the one you have now also
has a bad IC due to a condition that has not been corrected. Oops, I
see you didn't indicate that you changed it or that one was sent one
back. Maybe it is time (after you check other stuff).
6. Now let me take a best guess at the problem. Since you have already
eliminated the power supply, if you do the tests to make sure you don't
have any shorts on the control lines, remove surge suppressors and other
devices, and it still shuts down, then it has to be the controller box.
Reason: The voltage to the control electronics is dropping too low or it
will not operate without a higher than normal input voltage. With no
shorts, there should not be an excessive load. So something inside the
controller is malfunctioning.
Bill Carnett wrote:
>Greetings to all Tower Talkers,
>A very wise man and fellow TT (K7LXC) suggested I post
>my challenge here to the group...maybe somebody will
>have a new idea that I've not explored.
>Last week we put up a new 4L SteppIR with a 40/30
>dipole. The antenna is approximately 500 feet from
>the shack. SteppIR control line is used, continously
>without any accessories inserted, running through 3
>inch conduit (not that that makes any difference).
>Prior to lifting it in the air I found that a problem
>existed. When attempts were made to change bands or
>even frequency on the same band, the control box went
>dead. Simultaneously, as the box died, the "on"
>indicator light on the pwr supply went out. A second
>later the pwr light came back on; the led "lights" on
>the control box flashed once but the box remained off.
> The box could be turned back on, but the same
>sequence occurred if a band/freq change was attempted.
>Immediately all of the wiring and continuity was
>checked with the antenna...all ok. Spoke with Jerry
>at SteppIR and we proceeded to change first control
>box....before I realized the pwr supply was
>The next step was to attempt to run each motor
>individually and in groups. Each motor ran
>individually without problem. Adding the 2nd and 3rd
>motor caused no problems....the yagi functioned fine.
>The addition of the 4th motor (didn't matter which
>sequence), consistently killed the antenna. On
>occassion it would all seem to work for a couple of
>band changes but never more than 1 or 2 minutes - with
>all 4 motors running. So, with up to 3 motors
>running...all ok, with all 4, no go. However, this is
>a 4 element yagi. After speaking again with Jerry, I
>was reassured that the problem was simply a power
>supply and all will work fine....thus the long
>scheduled antenna raising event went forward as
>scheduled. Needless-to-say, the replacement power
>supply did not correct the problem.
>Prior to erecting the yagi I extended the elements to
>14150 so it can be used as a monobander...but that
>will only bring temporary happiness. A power supply
>(3rd) was "hand picked" by the SteppIR engineers,
>sent, and tested this morning. Basically the same
>problem. It did seem to work briefly then shut
>down....exactly the same as before.
>So, I'm looking for ideas that have been overlooked.
>Yes, I should have listened to my gut, rather than the
>"experts" and canceled the raising until all problems
>were fixed, but that can't be undone. If this beast
>must be lowered, I'm a bit reluctant to put it back up
>after this experience. Yes, all antennas have
>problems but it would be less $$ to replace it at the
>time of lowering rather then taking down, bring the
>crane back and forth, etc.
>Sorry for the long-windedness of this but any and all
>thoughts are appreciated!
>Moody friends. Drama queens. Your life? Nope! - their life, your story. Play
>Sims Stories at Yahoo! Games.
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