The power antenna in my 1982 300SD is not working, either with the radio on/off button or the dash-mounted up/down switch. I've ruled out the dash switch (harness has power; switch tests fine with an ohmeter). I haven't tested the radio further, but I don't think that's the problem.

At the antenna's 6-pin connector, #3 is ground and #4 is blank (plastic pin). With the radio off and the dash switch in the center position, there is 12V power across #s 1-2 and 1-3.

I removed the unit from the car and opened the cover. With power applied to pin #5, the relay clicks, then clicks back when power is removed. But the motor doesn't operate. On the other hand, if I disconnect the motor leads from the circuit board and apply power directly to them, the motor works fine in both directions and extends and retracts the mast. So the problem is clearly not the motor or mast. Also, the little ratchet gear that opens and closes the three contacts is fine, as are the contacts.

From reading other threads on this topic, I understand the circuit board in these units can fail. Is there a way to troubleshoot the board to pinpoint the problem, and possibly repair it? I'd rather not pay Walter Odemer $110 for a new (or rebuilt) circuit board. BTW, the Hirschmann part number on my board is 720 393.

Any other suggestions would be appreciated.