KD4APP G5500 Repair Page

Problem 1 (Early 2003)

I was having some problems with the azimuth analog readout on the control box - it was giving sporadic readouts between 225-320 degrees. I could move the antenna in that range and Uni_Trac could sporadically read it digitally in it's software correctly and control the rotator correctly.

I first took the azimuth cable connector off, re-soldered fresh ends and put it back on with the same results, so it appeared not to be a cable problem.

Next I took down the rotator and disassembled it because it was suggested that the feedback potentiometer wiper was dirty. I found that the black wire from the center of the internal wiper was barely touching the red wire where it was supposed to be soldered. Below is a picture where I pulled the black wire up to strip and tin the end before re-soldering it - when completed the black wire end connected to the red wire.

After reassembling the rotator I found that the rotator stopped at 90 degrees on the meter and would not go down to 0 degrees - took the four bolts out that held the rotator halves together and rotated the top 90 degrees clockwise - bingo it worked 0-360-90. The lesson learned is, next time mark the case halves so I will know where to line them up at reassembly time.

Feedback pot
(click picture to enlarge)

Problem 2  (September/October 2003)

My G5500 Control Box had blown a fuse so I replaced the fuse and it blew the replacement - I climbed up on the roof and discovered my coax cable to my UHF antenna had the N connector pulled off of it - for some reason the azimuth rotator had bound.  A few days later when I found time I called Yaesu and had them send me a schematic of the control box - after troubleshooting I discovered that the control box blew the fuse with no load on the output side of the transformer.  I called Yaesu to find a replacement transformer but they wanted $107 plus shipping for a replacement OEM transformer - I posted a message to the AMSAT-BB where John Beanland of Spectrum International (Uni_Trac Distributor) replied with the voltages needed for the output of the transformer and part numbers for two Radio Shack transformers that would be suitable replacements.  I obtained the two transformers listed below for around $20 total at my local Radio Shack.  The new transformers work great for my elevation rotator (from either side), unfortunately I still have a problem in my azimuth rotator which is probably the root cause of the control box problem - stay tuned for more details as I take the azimuth rotator down and troubleshoot it.

New transformers shown in control box above.

Part Number Description
273-1365 12.6v AC 450mA - to run lamps and electronics
273-15128 25.2v AC 2A - to run rotator motors

Problem 2a  (September/October 2003- January 2005)

After fixing the above transformer problem I still can't get the AZ rotator to turn - the EL rotator will turn connected to either side of the control box - I am currently investigating problems with the motor.  It is possible I may need to rewind the motor.

MVC-563F.JPG (177675 bytes)  MVC-564F.JPG (124908 bytes)  MVC-565F.JPG (168865 bytes)
Fig 1                   Fig. 2                  Fig 3

Looking at Figure 3 you can see the enamel wire coating is now dark black and has come off the wire.  I am preparing to build new winding forms and rewind the coils.

Update - January 2005

I just didn't have the time to wind my own coils so I called Yaesu and ordered a new motor - the motor I received (the correct one per Yaesu) had a plastic gear - I took the motor apart and used only the parts I needed to repair my current motor with the metal gear.  The rotator is now working 100% - just like new.

Contributed Information

Contribution 1 - Thanks to VA3DB - Diane Bruce 

I have been plagued with mysterious noise on 2m, on 14mhz on 10mhz on 29mhz.  After a lightning storm, I had unplugged everything. I plugged everything back in to work an ao7 mode A pass. Suddenly, there was that darn weird noise, sounded like a buzz saw. On a whim (after all, it had only started happening after I turned the rotor controller back on) I turned off the power on the controller. Noise/oscillation went away. oops.

Follow-up/fix below...

I put a scope on the output of my 7806, in the controller, it was oscillating nicely. It is not supposed to do that. The bypass Yaesu have on that is merely a ceramic, its not adequate for a voltage regulator. Bad bad Engineering, I suppose it saved a few pennies. Anyway, I stuck a 4.7uf 25v tantalum on the output of the regulator, bye bye oscillation. Its not strictly "by the book" as far as what is recommended, but it did the trick.

Hope this helps others.  Photograph included.

7806_mod.jpg (116423 bytes)

- Diane VA3DB



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