[amsat-bb] G5400B Rotor Problem

Joe Leikhim rhyolite at nettally.com
Sun Nov 25 14:23:22 PST 2012


The rotor turns a bit beyond the 180 degree clockwise mark, so when setting it, you have to observe the position of the AZ rotor bell. This is hard to do if the rotor is on the tower. You may need a helper and some walkie talkies.

Start with checking the voltages from the controller box.

The regulator Q2 (UA7806C) provides about 6 volts through 15 ohm resistors to screw terminals A1 and E1 on the rear panel. (A2 and E2 return a variable voltage from the rotor pots, while A3 and E3) are ground returns). I measured about +5.9 volts at A1 and E1 on mine.

Last month I was discussing a stability problem with Tom K4TB who advised me that he found the regulator Q2 would oscillate and the output capacitor C9 (0.01) ineffective, so he added a capacitor directly to the output and fixed his. The original Thompson datasheet for that device claims no output capacitor is required, though a National Semiconductor version of that regulator recommends a .22 uf cap at the input and a 0.1 uf cap at the output to "help transient response". Common wisdom has been that these devices may oscillate. I have seen some fluctuation in meter reading on mine at low end of scale.

I am in process of system testing my rotor and a TAPR TrakBox on the bench, so I recently set the voltages up to correctly display the azimuth and elevation. There are two pots on the corners of the rear panel which set the meter full scale accuracy these are VR1 and VR2. After adjusting these per the manual, page 4; Pre-Installation Adjustments.

After confirming the meters track the rotor position faithfully, there are a second inner pair of pots VR3 and VR4 which set the full scale (AZ and EL needle to full right mark 180 degrees)voltage at the DIN connector which is normally used to feed an ADC inside an external tracking interface like the TracBox or Kansas City Tracker, etc. I set mine to accomodate the ADC voltage range of the TAPR TrakBox, normally 5.0 volts at full scale. Set to this voltage even if you don't have automation, so if you automate later, you save from the headache if the voltage is way too high or low. These outputs should track 0-5V as you go from left to right on the meters.

If you are going to adjust these 4 pots, you might want to splash some volume control cleaner at them so they track smoothly.

Date: Sun, 25 Nov 2012 13:31:29 -0500
From:<tokens at myranch.com>
To:<amsat-bb at amsat.org>
Subject: [amsat-bb] G5400B Rotor Problem
Message-ID: <4C58B102B2AC45A7AD70C87ED4F77C10 at AlPC>
Content-Type: text/plain;	charset="UTF-8"

Hi all,

Trying to get a G5400B rotor going but having some calibration problems with the azimuth settings. With power off and the rotor set at the left hand position, I adjust the needle to read 180. When the power is turned on the reading goes to about 182. I then let the rotor go all the way to the right 180 mark and adjust the full scale pot to read 180. The problem is when the rotor is half way around and should be reading 360 it actually reads 345. Any ideas on what I should be looking at? Also there is nothing in the manual to suggest what the ?out voltage adjust? pot is supposed to do. What is its function?

Thank you for any advice.

73 Al W8KHP

Joe Leikhim

Leikhim and Associates

Communications Consultants

Oviedo, Florida

JLeikhim at Leikhim.com



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