A local amateur handed me his ATAS120 autotune antenna after a technician suggested to write it off as unrepairable due to the extent of water damage.
The amateur was surprised that it was water damaged as he had hardly exposed it to any rain, but he had recently purchased it from another ham, so it was likely that it may have happened earlier. Even so, he had hoped that it could be salvaged.
I disassembled the antenna and found that although substantially water damaged, it may be repairable.
Monday, 1 Feb 2010 20:23
The antenna arrived partially disassembled with screws and smaller components in small plastic bags. The main part of the antenna was not apart as the top section had siezed due to the water damage and was firmly locked to the main shaft.
A hidden screw was located beneath a label which had to be removed before the top section was clamped in a vice and pressure applied to the shaft in order to seperate the two.
The section which was clamped to the vice was protected by wrapping it in an piece of old drive belt, however the soft aluminium still deformed due to the pressure. The deformation was minor and probably could have been prevented if wooden clamps had been machined to apply even pressure around the circumference of the aluminium section.
With the antenna apart it was obvious that the coil had tarnished, all iron based components had rusted and that a film of oxide was present on the remaining components.
Applying a current limited 6V DC supply to the motor revealed that it was seized also.
CRC 2-26 spray was then used to displace any water in the motor and gearbox through whatever access could be gained. There was no clear entry available to the internals of the motor, so I'm not sure how effective the exercise was.
The gearbox was disassembled by prying apart the metal tabs holding it to the motor.
The gearbox did not appear to have had been damaged by water, but it was full of silicon grease and made of nylon.
Gently rotating the motor shaft backwards and fowards released the motor and although it sounded 'gritty', it did rotate, drawing between 0.5 and 2.5 amps at random. This meant that there was water damage and I tried to spray some more 2-26 into it and let it stand for a while.
I then removed and cleaned the controller board, using a fibreglass pen to clear oxide from the earth contact that had formed at the base. I had to pick oxide away from the surface mounted components using a micro screwdriver and a magnifying lens.
Once cleaned, I used Isopropanol and an old toothbrush to clean the board. This seemed to do the trick.
The board seems to have been factory coated with a PCB lacquer which prevented the oxide layer from going underneath the smd components. Had it done that, it would have been necessary to remove them prior to cleaning.
The coil was restored by brushing it with a small modellers brass wire brush. This brought back the wire's lustre and removed the oxide layer that had formed on the copper (which would have increased its contact resistance).
Yaesu ATAS 120 Autotune Antenna Repair
After re-assembling the motor and gearbox assembly, I placed a current-limited 5 Volts directly to the motor and noted that it turned fine. I then reversed polarity and again the motor turned fine.
After a few more tries I noticed that the motor current was not constant, indicating that there was varying load. Further testing revealed that the internals of the motor had also been affected by water and that spraying WD-40 onto bush bearings seemed to help. Ideally it would have been a good idea to disassemble the motor and flush it with WD-40 however the more I used it, the better it became so I didn't risk it.
The repairs seem to have done the trick and everything looked ok. I've since returned the antenna to the owner and time will tell as to how effective the repairs were.
I'm not sure how the antenna seemed to have so much water ingress. All of the seals were intact and there were no obvious modes of entry.
The only thing I can put it down to is that if the antenna is operated in the rain, that possibly it acts like a set of bellows, so when the antenna is at its shortest and then is raised in the wet, it sucks in any moisture that is on the lower section. After repeated raising and lowering, its possible that this water accumulates inside the unit as it has nowhere to drain.
That's only a guess, as I can't see any other explanation for why water should be able to enter a virtually new antenna with perfectly intact upper seals.
Replacement Motor Update:
I was advised by a US ham that he was able to obtain a replacement motor for the ATAS 120 from Austin Amateur Radio Supply in Austin Texas for around $50.
If you need to have your ATAS100 or ATAS120 repaired, there is a fellow ham, Tom Dailey, W0EAJ, with a repair business in Denver,CO called Tom Dailey's Vintage Radio Repair that may be able to help you.