[amsat-bb] Re: 5400B Rotor problem Help

Alan ve4yz at mts.net
Tue Dec 18 09:35:47 PST 2007

Hi Bill... when you check the schematic for the G-5400B you will note that
the AZ and EL circuits are identical from the rear terminals thru to the
meters.  The meters are identical except for printed scale on the front

When I had a problem with my read out - it just failed total one day to read
anything while the rotator functioned ok, I was able to compare voltages
between the 2 identical circuits.  i.e. full CW compared to 180 degrees and
full CCW to 0 degrees.  Now I can't remember which comparison worked CW or
CWW with 0 or 180 degrees but you can figure that our quick enough.  I don't
flip my antennas so what I was really comparing was 0 to 90 degrees vs North
to the 2 South positions.   This involves a lot of running up and down the
stairs from the basement shack to outside to check the true antenna position
on the failed unit. For those with similar problems with a failing EL read
out the 0 degree is easy to set as the EL has a limit switch and you can see
when it opens by the increased brightness of the meter which it switches.
90 degrees requires a visual confirmation.

In my case I found everything measured the same up to the op-amp so I had no
choice but to replace it.  They are readily available for under a buck.  The
desoldering of the IC was tricky ( no room for a chip puller ) so when I
went to replace the IC I soldered in a socket instead.  

Here is the end result:


I have 3 G-5400B systems I monitor - mine, a club station and my
father-in-law. So I also know those meter lights soon fail.  So while I had
the box open I replaced the 2 bulbs.   Although I've seen comments on this
BB about replacing the incandescent with a LED, I found the white/clear
unsatisfactory as its plastic case was also a lens for focusing the output
out like LED flash light and it produced a "hot spot" on illumination of the
meter. So I reverted to an 12V incandescent from Radio Shack ( The Source up
here in Canada ) with a diode in series.  The reduced output from the bulb
was bright enough and now it will burn longer than me.  Just click the "View
Album" on the above link to see all the rebuild photos of my 5400B system.

Final note: for those of us up in the Great White North, and, I suspect it
applies to the Scandinavian countries as well; part of the rebuild includes
replacing all the grease with low-temp stuff so everything works at -40
degrees.  Centigrade, Celsius, Fahrenheit - it doesn't matter which you
choose at -40.

73, Alan VE4YZ

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Bill Bruno
Sent: December 18, 2007 9:55 AM
To: Amsat-bb at amsat.org
Subject: [amsat-bb] 5400B Rotor problem Help

Thanks to all for the emails responding to my question.
I think my problem might be in one of the four wires that make up the
instrumentation circuit. Does anyone know what voltages I should be reading
on  these at specific headings?

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