Power Antenna Motor turns the WRONG WAY

[Icebound]

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My antenna was working properly and then stopped abruptly this past weekend. It was fully retracted and would not go up.

Did the power checks on the "from distribution" plug: all ok; orange is always-hot plus; black is ground, Green is hot when radio on. As advertised.

Further test showed that the antenna motor is actually turning the "wrong way"... going up, when it should be going down and down when it should be going up.

Any ideas what has happened??? There has been no recent maintenance on the electrical, and especially not on the antenna.

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The following lengthy bit is just to show the tests which were done:

On the antenna plug... The NORMAL operation is supposed to be:
to go "up" should be PLUS to the green and ground the grey.
to go "down" should be PLUS to the WHITE and ground the green.

Because of the way the limit switches work, I cannot simply swap the white and green to go "up" because the white is out of the circuit when the antenna is full down.

HOWEVER.... again, because of the way the limit switches work.... I could get the antenna to go UP, by applying PLUS to the GREY and grounding the green. (In proper operation, the grey never sees PLUS).

So NOW, once I get the antenna into the middle, both limit switches are closed and so all 3 wires are live. Applying Plus to WHITE and grounding the green makes antenna go UP; plus to the Green and grounding the grey makes the antenna go DOWN.... both are exactly opposite to what is supposed to happen.

With the antenna in the middle (where both limit switches are closed), I turn on the radio. Then I plug in the antenna relay. The antenna fully RETRACTS.

With the antenna in the middle, and the radio OFF, I plug in the relay and the antenna FULLY EXTENDS.

When the antenna is FULLY extended, turning the radio ON does not retract it...because of the way the limit-switches open. However, starting in the middle... having the radio on WILL retract it.

Similarly, when FULLY retracted, having the radio OFF, will not extend it because of the limit-switch operation....but from the middle, it WILL extend it.


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[Icebound]

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Just a little update...

Tried reversing the magnet over the armature.

Did not change anything.

[Icebound]

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Well, unless somebody else has an idea, I am officially declaring defeat.

A bench test of the motor with the case removed, confirms that it indeed rotates the wrong way.

Continuity tests correspond to the circuit diagram. There is supposed to be a capacitor across the motor (presumably for noise suppression) which I cannot readily spot. However, continuity across the motor shows 4 ohms (which would be the winding), and not a dead-short.... And if the capacitor was open, the worse that should happen is radio noise during the travel.

I tried minor adjustments to the brush configuration... a little higher on the commutator... a little lower.... Nothing changed except that the motor did not run as well.

I can't just rewire the plug, because of the way that the limit-switches work. A rewired plug would work fine until the motor reaches the end of travel. Then to get it to go the other way, I have to apply voltage through the limit switch on the side which is now open.

The only solution which I see, is to reverse the brush connections within the motor itself. This would be a delicate operation and I don't think the chances of success are very high. If nobody here has a solution and if I cannot easily find another motor in a few weeks, then I might attempt it.

But there really must be SOME reason that it reversed, and I don't want to attempt anything too drastic until I find out what it was...

In the meantime, I guess we run it up manually and leave it unplugged. BAH!


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[00Beast]

Could you switch the wires around? That would solve the up and down issues.

[willwren]

I suspect your nylon cord broke. Drill out the rivets and open the unit for inspection. Small machine screws will be needed for re-assembly unless you scrap it. Get a replacement from a 98 or 99 at the wrecker.

[Icebound]

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A final word: success, but we don't know why.


After declaring defeat, I reassembled it with the intent of installing, extending, and unplugging..... leaving it permanently "up".

I had to dissassemble-reassemble several times, because you have to get that little cog-wheel set just right so that the end-stops occur at the right place (otherwise it won't extent long enough, or won't retract fully).

In the course of all that, I reversed the field magnet several times, just for the hell of it...

And MAGIC.... after one of those reversals, suddenly it is working properly again.

Whether something got moved in the course of all that fiddling, or whether it was the magnetic reversal, or whether it was just "magic".... but once again "it solved itself", and I have a working antenna.

For how long, yet to be determined.


To willwren: no, this was an electrical issue, not a mechanical one. By the way, at 17 years, the nylon gear and cord, and the brushes, commutator, and limit-switch contacts, are all in remarkably good shape. The worst wear is, surprisingly, to the teeth of the metal worm-gear. I suspect a great many "bad" anntenna motors are not bad at all and just have some simple issue.


To 00Beast: you could reverse the wires, but the antenna would only work ONCE. With permanently-reversed wires, when it reaches the end of travel, the limit switch opens and there is no way to apply power to get it moving in the other direction. The antenna relay would have to a totally different schematic, for reversed wires to work. Check my posts carefully for the description of how that has to work.


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