One minor correction to what I just wrote. Each element requires 4
wires, not 2, but they when they are measured from the controller end
they will appear as 2 independent loads.
> 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 need.
> 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 unlikely).
> 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.
> Jerry, K4SAV
> 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
>> faltering....no change.
>> 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!
>> 73, Bill
>> Moody friends. Drama queens. Your life? Nope! - their life, your
>> story. Play Sims Stories at Yahoo! Games.
>> http://sims.yahoo.com/ _______________________________________________
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