Hirshman Antenna Rebuild/Mod Help
 

I disassembled the Hirschmann power antenna on my 1979 911SC and need some troubleshooting help and advice on a possible 'mod'.

With the radio switched on, the antenna motor doesn't run when connected to the three wires in the fender well. The motor runs perfectly if I disconnect the red wire and jumper that terminal directly to the battery 12v+

If I understand the connections correctly, white is 12v- ground to the circuit board, black is 12v+ to the circuit board, red is the 12v+ leg to the antenna motor. The red wire should be 'hot' only when the radio is switched on. Is this correct?

If so, I think the problem is the 12v+ red wire. Testing with a voltmeter, I get spurious readings at the red wire (radio on). At the black wire I get a clean 12v+

Any ideas why I'm not getting 12v+ at the red wire?

Everything inside the aluminum box seems to function normally, when I disconnect the red wire and jumper that terminal to the battery. The relay 'clacks' and the motor runs. The motor reverses if I operate the relay manually.

Second question:

I could probably connect the antenna motor to a toggle switch mounted under the dash and raise or lower the antenna to any height I want. This might give me a degree of antenna tuning capability that could help to bring in the radio's short wave bands.

Any opinions on this as a possible 'mod' ?

Thanks for your help!

piscator

and I have a burning question...
 

how do I get in there to get mine OUT so I can begin to troublshoot?
From inside the car? or inside under the hood?

bump
 

so....how do I get this guy out????

Don't know about SC's and removal. IIRC, the antenna gets a signal from the radio to go up or down, it doesn't send a continuous voltage to keep the antenna up. don't know about removal on the left side of the car, right side on a Carrerra is easy under the wheel well.

good luck.

I had to take the fender off of mine to get to the antenna, it was either that or take the door off. It sits in that cavity between the fender well and the inner door opening, at least it did on mine.

On the power antenna, I had a powered Hirschmann on a '69 Mercedes that did not power up and down as it was supposed to. I removed it, took the cover off to expose the mechanicals, and hooked up some little alligator clips directly to the terminals from a spare battery. Then it worked. Problem was some of cloth covered wiring had deteriorated, letting it short itself out. If that's the case, it's easy to see what wires are burnt, and they can be replaced. There are also gears inside that you can get to with the cover off that can be lubricated, which helped a ton. Just work it back and forth until it's smooth.

Thanks guys!

Scotricker, my antenna is mounted in the passenger side wheel-well. It quite easy to get to if you take the wheel off.

HughR, thanks for the tip. On my antenna the red wire feeds +12v directly to the motor. Up and down appears to be controlled by a plastic 'whirly-gig cam' that mechanically reverses DC polarity. Maybe my setup was constructed before Hirschmann started using an 'up/down signal' from the radio.

68911USA, I'm using the 'alligator clip method' as well. I cleaned and lubricated the gears as you suggested. The mechanism runs fine, when I power it 'on the workbench'. I don't have any burnt wires, but I'm not getting voltage to the motor from the red wire in wheel-well.

The red wire appears to be the 'hot' lead to the antenna motor, so it must be fused somewhere. I just can't find the fuse to see if it's blown. I can't find it in the fuse panel, so I'll check under the dash again and look around the battery.

Thanks again!

piscator

To answer my own questions for future readers, on my 1979 911SC Targa:

Inside the Hirshmann power antenna box:

The red wire (the one that bypasses the circuit board) supplies +12v to the antenna motor. The in-line FUSE for this red wire is tucked up next to the ignition switch.

The white wire to the circuit board is -12v ground.

The black wire to the circuit board is +12v from the radio.

There is no 'signal' from the radio 'telling' the antenna to 'go up or down', in my car. When the radio is switched on, the black and white wires operate the relay which opens and closes the circuit to the antenna motor.

Up and down are controlled by the mechanical 'whirly-gig' that cams the contacts against or away from the +12v 'rail' the red wire attaches to. This changes the polarity in the circuit and reverses the motor direction.

There is another fuse on a second red wire supplying +12v to the radio. I found mine tucked up above the unit itself.

Hope this is of some help.

piscator