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Post by 97 & 99 autobahn on Mar 2, 2018 3:31:52 GMT -6
On my 99, when I parked it yesterday I heard "Thumping " from the trunk ! I soon reallized it was my antenna "cycling & would only stop with key in start , power button on radio had no effect.had to un-plug harness on antenna ! never read of anyone else having these problems ?? Help !!
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Post by wfooshee on Mar 10, 2018 21:29:59 GMT -6
The thumping is normal, up to a point. The mechanism that extends and lowers the antenna is timed by a rotating disc (or cylinder, but I'll keep using "disc") inside, which rotates a metal bead beneath the electrical contacts supplying the motor. The metal bead doesn't go all the way around the disc, so when the disc reaches the point where no metal is under the contact, the motor stops. (Actually, the disc suppies ground or 12 volts, alternately, to one wire of the motor. The other wire is either grounded or energized by the remote wire from the radio - grounded when the radio is off, energized when it's on.) The thumping comes from a clutch, basically a spring-loaded ball in a socket. When the antenna reaches the limit of travel but the disc hasn't reached the end of the metal bead, the motor keeps turning, and that spring-loaded ball retracts to allow the motor to keep turning.
That's done so the antenna limits won't have to be subjected to precision adjustments. No need to stop the motor exactly when the antenna is all the way up or down. It can overrun because the little ball can pop down out of its socket., and the disc is set to give the motor plenty of time to reach the antenna's full extension or retraction.
It sounds like that disc may be broken, not turning, or another short somewhere in the electrics leaving the motor energized forever. The thumping is the ball engaging its socket every time around, then being forced to continue. It's probably not repairable other than by replacing the antenna assembly.
The power button on the radio had no effect because the antenna has never come out of "retract" mode. Once it leaves "retract" mode, powering up the radio triggers the remote wire and the antenna goes into "extend" mode, with the motor running until the contact is broken by the rotating disc, at which point, removing voltage from that remote wire will trigger its "retract" mode. It can't change modes until it stops, though, and unplugging the harness doesn't count as a stop, because the circuit inside the housing, that disc, hasn't reached the end of its metal bead. That rotating disc actually reverses the polarity of the power going to the motor. When it finishes extending, one side of the motor changes from ground to 12 volts. Since there are 12 volts on the remote line, the motor doesn't turn. No voltage difference. When you turn off the radio, the remote line is grounded, and the disc still has 12 volts applied to the other dies of the motor, it runs until the disc switches polarity again, with both sides of the motor being grounded, and it stops.
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Post by 97 & 99 autobahn on Mar 13, 2018 5:50:59 GMT -6
Thanks WFOOSHE
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