intermitent antenna problem - self retracting - PeachParts Mercedes-Benz Forum

sljoe · #1 10-21-2008, 08:14 PM

I have a strange (I think) problem with my 95 sl antenna. The problem is that the antenna will just retract by itself for no reason. The radio is still powered on with the face still lit and all front panel buttons functioning. However, there is no sound and the antenna is down. If I turn the radio off and then back on, the antenna may come up but lately this is not the case. Now it appears that when I turn on the ignition the antenna starts to come up and then retracts right away. This has been happening for a while ( antenna up and radio working but then retracting on it's own) but now it is worse than it has been, happening more frequently and now I don't knowif it will ever come up again. Is this a problem with the radio, antenna or someting else? I'm sure the antenna mast and motor are both fine. Any advice will be appreciated. I searched the threads but didn't find anything like this.

tecqboy · #2 10-21-2008, 09:31 PM

I'd use a volt meter to check for the 12volt control signal at the connector on the antenna mechanism. It should be 12v with the radio on. Sometimes the limit switches in the antenna mechanism go bad. A limit switch "tells" the motor which direction to turn and when it is at the end of it's travel. There is an "up" limit switch and a "down" limit switch inside the housing.

sljoe · #3 10-22-2008, 09:53 AM

Tecq,
Thanks for the reply, I'll give it a try. If it is the limit switch, is that a replaceable item that can be purchased somewhere? Also if the antenna, when working, fully extends and retracts could it still be the limit switch?

If I'm not getting 12 volts at the connector, is it an issue with the radio supplying the 12 volts? If so I guess I will have to send the radio for repair, right?

tecqboy · #4 10-22-2008, 10:52 AM

Although the control voltage comes from the radio, the actual power for the motor comes from fuse 6 in the trunk fuse panel, so check that for looseness or corrosion. I've never seen a radio fail this way, although anything is possible. But power antenna mechanisms are notorious for failure. Although a do it yourself'er could probably replace a broken limit switch, in the real world, replacing the entire power antenna may be the route of least frustration ( where do you find a new switch ?). The nylon cord is sold as a replacement item. Do an internet search for hirschmann antenna. But I'd make absolutely sure the power and control voltage were OK first.

RadioTek · #5 10-23-2008, 12:55 AM

This sounds like an intermittent connection problem. Something's loose or worn out of spec. Some of these systems use a relay to control the antenna, so that could be a place to look: the more connections, the more places to have problems.

Sometimes, you can get lucky and find something by just looking at everything and gently pulling or pushing to find a loose connector, corroded terminal, or 'barely hanging on' wire.

Don't be afraid to look for the easy, obvious problem. Sometimes that's the solution. Reseating a loose connection before replacing a good unit on suspicion. I've seen way too much of that over the years. The process is called 'Easter Egging', and is a mark of a bad tech.

How can you tell a ######## field engineer with a flat tire?
He's the one changing one tire at a time until he finds the right one.
(Old computer industry joke)

sljoe · #6 10-23-2008, 04:21 PM

Radio,
Thanks for the input. I will try to see if I can find a loose connection. It does seem to be more along these lines because of the intermittent nature. Although lately (precipitating this thread) it just starts to come up slightly, maybe 1 - 2 inches and then retracts but there are still times it won't come up at all. It always seems to try to come up during key starts but not when turning the radio off and on. Unfortunately, I'm not real good at tracing wires.

RadioTek · #7 10-23-2008, 04:47 PM

Tracing wires on these things can be an art form. I would suggest a good manual, the best being paper, but they are rare, next, a CD ROM manual, or a Hanes book. These usually have the color codes and connection points. A simple multimeter is also an invaluable tool for electrical troubleshooting.

Taking some time to learn how to use these tools can be a rewarding experience. The feeling of accomplishment when you hunt down and (figuratively) stomp on a bug that's been deviling you for a long time is _very_ sweet. The more knowledge you have, the easier it is to fix things.