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Re: Yaesu G-5500 debugging help request




> In any event, the elevation meter reads 0 deg no matter what position I 
> move the rotator to--from 0 to 180 degrees.

Make sure the voltage is making it to the rotor by measuring the
voltage between pins 1 and 3. The voltage should be close to what 
you measure at the rotor control box minus any voltage drops along
the way. This test will help isolate the problem. It is either in your 
elevation rotor or the cable. Keep in mind that your elevation cable 
encounters motion and flexing that your azimuth rotor does not 
experience. You may also try wiggling the elevation cable at the rotor
in different directions when making the measurement. If you are not 
measuring much voltage between pin 1 and 3 at the rotor, then your 
cable is a problem. If this test is good, then try measuring between pins
2 and 3 to see if you measure anything. It is helpful if you can move the 
rotor at the same time when making this measurement. You do not 
need to move it very much to see a change in voltage.

If all of the above is working, then try removing the rotor cable from the 
elevation rotor and measure the resistance between pins 1 and 3. You
should measure 500 ohms if my memory serves me well. I have had 
to replace about 5 of these in the past 10 years from lightning strikes on
my rotors. Now, measure the resistance between pins 1 and 2 and then
measure the resistance between pins 2 and 3. The sum of these two
resistance measurements combined should equal the value measured
between pins 1 and 3. If not, your rotor will need some surgery to find
the root cause of the problem between the terminal strip and the 
potentiometer inside the rotor.

 
> Obviously it could be one of the wires to the position pot (it's just a 
> variable resistor pot, right?), or the pot has gone bad.

Yes, it is a linear variable resistor (not cheap either). A wire inside the
rotor is not likely to go bad without a good reason, since it does not
move inside the unit (at least it should not be moving).


>  From what my meter tells me, it seems like contacts/screws numbered 1 and 
> 2 (on the back of the controller, where the wires run to the rotators) are 
> involved.  Seems like contact 1 is the reference voltage (measures 6.12 V 
> DC on the EL side, 5.94 V DC on the AZIMUTH side), and contact 2 is the 
> feedback/position voltage.

Pin 1 on your rotor control box supplies the voltage to the rotor. Pin 3 is the
return line and pin 2 is the voltage feedback from the wiper on the potentiometer
located in the rotor.


> On the AZIMUTH side contact 2 varies from nearly 0V (0 deg) to ~4.35V (360 
> deg) ; all looks well.   On the ELEVATION side, it is interesting--while 
> the meter doesn't move, contact 2 reads about 0.5 millivolt at 0 deg, 4.0 
> millivolts at 45 deg, and 8 millivolts at 90 deg.  So, it's "sort of, kind 
> of" working.

No cigar. Do you see the meter jump at anytime through the full motion
of the elevation rotor?  The elevation rotor cable receives far more stress
than the azimuth cable. Check the cable that goes around the azimuth
rotor to the elevation rotor. You might need to cut this section out and pull
the cable up and prepare the wires to reconnect to the elevation rotor.

>From what you have described, the problem is between the rotor control
box cable and the rotor (including the rotor).


> Any of you G-5500 repair/debug experts have any advice?
> 
> How about instructions for replacing the position indicator resistor 
> pot?  Seems like I've seen that on this BB before.

You can order the potentiometer from Yaesu.



73's and Good Luck!

Tim - N8DEU
Huntsville, Alabama



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