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Re: [TowerTalk] SteppIR problem

Subject: Re: [TowerTalk] SteppIR problem
From: K4SAV <>
Date: Sun, 10 Jun 2007 22:16:39 -0500
List-post: <>
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.


K4SAV wrote:

> 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 
> 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
>> 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
>> ____________________________________________________________________________________
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