[amsat-bb] Re: G5400B Rotor Problem

i8cvs domenico.i8cvs at tin.it
Wed Nov 28 13:54:28 PST 2012

Hi Al, W8KHP

Normally I have seen the resistance of the potentiometer to be less than 500
ohm but this is not extremely important.

BTW is very important that the potentiometer is linear.

I suggest to rotate the azimut just mid way of it's travel i/e 180° one side
and 180° to the other side up to both the mechanical stops.

Disconnect the wires A1 A2 A3 from the rear of control box and than
measure the resistance between A1 and A3 as well the resistance between
A2 and A3

If the potentiometer is in good shape both resistance readings must be the
same value less than 250 ohm each side but the same value.

Have fun

73" de

i8CVS Domenico

----- Original Message -----
From: <tokens at myranch.com>
To: <amsat-bb at amsat.org>
Sent: Wednesday, November 28, 2012 10:00 PM
Subject: [amsat-bb] G5400B Rotor Problem

> Got some unexpected time today to look at the rotor. First I set the
output at pin 6 of the external control output jack to 5.0 V. Then I got
readings every 45 deg from 180 at the left to 180 on the right. The readings
are of course subject to parallax in reading the needle. Readings from 180
on the left to 180 on the right were 0.024, 0.606, 1.270, 1.864, 2.489,
3.074, 3.690, 4.350, and 5.000 V. The difference in voltage from reading to
reading varied from 0.582 to 0.660 V. From left to right they were 0.582,
0.664, 0.594, 0.625, 0.585, 0.616, 0.660, 0.650. I then took resistance
readings on the 500 ohm pot in the rotor (removing connection from control
box each time). Starting at the left resistance from 1-2, 1-3, 2-3 were 415,
416, and 1.7 ohms. With the rotor halfway around (360) (dial reading 345)
resistance from 1-2, 1-3, 2-3 were 241.7, 416, and 176.1 ohms. With the dial
at 360 resistance from 1-2, 1-3, 2-3 were 220.4, 413, and 193.6 ohms. With
the dial at the right 180 resistance from 1-2, 1-3, 2-3 were 30.4, 414, and
383 ohms. First observation is that the pot in the rotor is considerably
less than 500 ohms. Next with either the rotor being halfway around or the
dial reading as if it were halfway around I would expect the 1-2 and 2-3
readings of the pot to be somewhat similar but they are not. So, are these
results glaringly pointing to the 500 ohm pot as the culprit? Or does
someone see something else?
> I’d appreciate any opinions on this. Thank you once again.
> 73 Al W8KHP
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