Question on 740 power antenna:

  • Thread starter Thread starter geronimo
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geronimo

Its my 92 740 turbowagon. The antenna was gone, snapped off at
base. I bought a new antenna and installed it. The plastic track to
make it go up/down went in OK. However, the motor doesn't work, so I
just installed it extended. I opened up the panels and to my surprise
I found that the motor isn't electric...its a vacuum operated motor
with two lines going to it. SO I started the car and tried it....
with the dash switch in either position, there is no vacuum on the
clear line (the black one doesn't come on/off with a barb fitting
like clear one does). My guess is that the switch is not electric at
all either but its a vacuum switch. Haven't torn into the dash to
check that out yet.
Anyway, how to troubleshoot where the vacuum to operate the antenna
is being lost?

Thanks, geronimo
 
geronimo said:
Its my 92 740 turbowagon. The antenna was gone, snapped off at
base. I bought a new antenna and installed it. The plastic track to
make it go up/down went in OK. However, the motor doesn't work, so I
just installed it extended. I opened up the panels and to my surprise
I found that the motor isn't electric...its a vacuum operated motor
with two lines going to it. SO I started the car and tried it....
with the dash switch in either position, there is no vacuum on the
clear line (the black one doesn't come on/off with a barb fitting
like clear one does). My guess is that the switch is not electric at
all either but its a vacuum switch. Haven't torn into the dash to
check that out yet.
Anyway, how to troubleshoot where the vacuum to operate the antenna
is being lost?

Thanks, geronimo
Click to expand...


Vacuum? That's weird, I know for a fact the '87 antenna motors are electric.
Sure you're not just looking at the moisture drain?
 
Hmm......maybe? I am seeing the bottom of a metal cylinder abt 1 in
wide, and there is a black 3/8 plastic tube (or cable), as well as
simiilar size clear tube, both connecting to the bottom. Guess I will
look closer at that black tube and see if its maybe actually an
electrical cable. Its like permanently sealed to the bottom, with no
sign of connections on outside. You're probably right, the clear tube
must be a drain, and inside the black tube/cable there are probably
wires.
I have checked for a blown fuse for accessories and none were blown.

thanks, Geronimo
 
geronimo said:
Hmm......maybe? I am seeing the bottom of a metal cylinder abt 1 in
wide, and there is a black 3/8 plastic tube (or cable), as well as
simiilar size clear tube, both connecting to the bottom. Guess I will
look closer at that black tube and see if its maybe actually an
electrical cable. Its like permanently sealed to the bottom, with no
sign of connections on outside. You're probably right, the clear tube
must be a drain, and inside the black tube/cable there are probably
wires.
I have checked for a blown fuse for accessories and none were blown.

thanks, Geronimo
Click to expand...


In the wagon, the motor and spool assembly is located in the lower area down
below the window and drives the antenna mast through a cable enclosed in a
plastic sheath similar to a bicycle brake cable. What you're seeing is the
sheathed cable and the drain tube which run down to the motor.
 
YOu got me on the right track alright. Pulled up that side floor panel
and there it was. There is a control module for the motor, and when I
opened it up, I see the very bottom edge of ithe circuit board got
immersed in water, and shows massive corrosion. Good news is that the
only semiconductors on board (other than power supply diodes) are two
7400 QUAD NAND ICs. I think I even still have some of them in my
electronic junk box. Shouldn't be too hard to repair the PC board. I
tempirarily cut sires to the motor and touched to power/gnd in both
polarities, and the antenna goes up/dn just fine....so a new or
repaired module is definitely what it needs. Thanks, Geronimo
 
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