Preston's Radio

["Al Powell" <APOWELL@agcom.tamu.edu>]

> From: Preston Brown <pbrown@econ.yale.edu>

> However, the antenna still doesn't raise.  It is getting the "turn on" 
> power signal from the radio plus another +12v on the red wire directly 
> from the battery, so it should be operating according to some.  However, 
> it isn't.  I have taken the antenna motor apart, (lots of grease!) but I 
> really don't know where to start testing.  The motor itself has three 
> leads(why?) going to it.  

Should be positive, negative, and the relay to make the connection 
when the radio is turned on.  If those are working, my bet is the 
motor is gone.

>I can get continuity across two of them.  

Seems to me like one (-) should always have continuity with the body, 
one should have 12 volts at all times (the +) and the third (relay) 
should show 12 volts when the radio is on.  (Haven't ever checked 
this, but that's the way it seems like it oughta be... and the way 
you've described it.)

> There 
> is also a small PC board with some resistors, diodes, a transistor, and a 
> capacitor, and two wire-wrapped things (relays?).  What's this stuff for 
> anyone?  Circuitry to stop/start the motor when the antenna is fully 
> raised/lowered?  

Seems like that's the deal....but trouble-shooting without a diagram 
and values for the components is almost impossible.

> Anyway, I need some help fixing this thing if anyone 
> wants to help me -- I don't want to just "replace" it without knowing it 
> is truly broken.  If I can determine it is broken and beyond my repair 
> skills, I'll go scavenger hunting for a new one.

Well, here's what occurs to me.  IF the situation is as is theorized 
above - with 12 v. present on one wire, (-) continuity on the other, 
put 12 volts into the third and see if the motor makes noise.  If 
not, the problem should be either in the relay which actuateds the 
motor or the motor electronics.  In either case, a Hirschmann 
or Harada motorized antenna replacement would be in order....the 
Hirschmann has a mast which can be replaced in 30 seconds for $18.

If you'vae actually done this - and it sounds like you have - then 
I'd proceed to replace the antenna....NOT with a factory one, but 
with one of the makes I've mentioned.  I installed a Hirschmann 
in my 1984 5KT and it's great....a direct replacement.
Al Powell                           Voice:  409/845-2807
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