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 panel.
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:
http://picasaweb.google.com/ve4yz.alan/RotatorRebuild1999/photo#514535783358 9963522
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 EN19 AMSAT LM 2352 http://www.mts.net/~ve4wsc/ AMSAT A-485
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bill Bruno Sent: December 18, 2007 9:55 AM To: Amsat-bb@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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