Friday, December 25, 2009

ATAS-120A Disassembly and Cleaning

Here are some notes about how to disassemble, clean, and assemble the Yaesu ATAS-120A motorized screwdriver antenna. Mine's a few months old now, and I've taken it apart a few times to check for corrosion or other problems ... so far so good!


There is a schematic for the ATAS-120 available online if you search for it. If you're going to do any work on the antenna, it's a very good idea to take a look at how the unit is constructed in the diagram below:

First, remove the ATAS-120A from the vehicle mount:

Personally, I like to use a little bit of coax seal to add weatherproofing to the cap. This is removed next:

Remove the coax seal:

Grab the rubber weatherstripping boot on top:

And slide off the boot, exposing the hex screws that anchor the whip:

Loosen the hex screws:

Remove the whip and the boot and set it aside:

Now take the hex screws all the way out:

And carefully set them aside as well:

Once the hex screws securing the top of the weather shield are removed, the outer weather shield (which Yaesu calls the Cover Assembly) can slide right off. Push upwards from below:

Now you can set the outer cover assembly aside:

Next step is to remove the base containing the matching assembly. Pull up on the rubber ring:

There are three silver screws underneath the ring:

Remove the silver screws:

Note: I've actually replaced one of the nylon washers with a stainless steel lock washer, and have buffed off the paint where the screw/washer connect to the black tube. The reason for this is to maintain a good RF contact between the matching assembly and the top tube, overcoming any potential open circuits caused by an inner O-ring, the nylon washers, and the paint and possible corrosion. The screw / lock washer assembly can be sealed with a small amount of coax-seal around the perimeter of the screw.

And put a matchmark between the tube and the matching assembly for later assembly:

Now the tube is unscrewed from the base, carefully work the matching assembly off of the tube. There's no way to stress this enough. Carefully. CAREFULLY. Once that O-ring on the base is clear of the tube, there is NO friction holding the two together and it's super easy to yank the motor wires right out. Slowly and carefully:

Carefully slide the matching assembly out of the tube:


You can now see the motor connector, it unplugs easily:

Unplug the motor connector and separate the top from the matching assembly:

Set the matching assembly aside:

One thing I have noticed is that over time, the connection between the matching assembly and the outer tube can become intermittent. Symptoms of this are "fluttering" on receive, reports of clipping in transmitted audio, and intermittent continuity when checking tip-base circuit with an ohmmeter while "wiggling" the tube against the match. Partly because of corrosion, partly because of the rubber O-ring, and partly because of the nylon washers on the three screws that secure the tube, it really isn't the best connection. What I have done is to clean the top of the matching assembly thoroughly, then clean the inside of the tube. Adding compound like anti-sieze (to prevent the tube from corroding to the matching assembly, as some have reported) only seems to make the intermittent connection worse, so instead of this I've just been keeping the whole connection clean. Also, the use of a steel lock-washer instead of a nylon washer (above) helps to maintain a good RF connection between the match and the rest of the antenna.

And now make a matchmark where the top assembly (which Yaesu calls the Terminal Holder) inserts into the tube:

There are three black screws in the middle of the tube. Remove them:

And set the three black screws aside:

Next, remove the three silver screws securing the terminal holder to the top of the tube:

Note that one of the screws is secured under a silver label:

Slide the terminal holder assembly out of the tube:


And separated:

Now you can see the entire coil, motor, and terminal holder assembly:

The black tube is just a hollow aluminum tube:

Here's a view of the motor assembly:

And a view of the coil and terminal holder assembly:

Here's a close-up of the terminal holder assembly. The silver springs secure two ball bearings each. The ball bearings connect the slider (fixed in the outer black tube) with the wire coil (which slides in and out).

After 6 months of mobile operation, I was starting to get a little "fluttering" on the antenna as it moved. It turns out the spring clips over each ball bearing weren't pushing down quite hard enough, allowing the coil to move against the balls. Simply unscrewing the small philips-head screw securing each spring clip, and slightly bending the clips inwards towards the ball bearings, and reinstalling, solved the problem. You can see the clips clearly in the photo below:

My coil had fine "grooves" in the wire where the bearings ran over them (after 3 months of use), along with a fine copper dust inside. Reportely, this is normal.


Assembly is simply the reverse of disassembly. Be sure to avoid catching the motor leads when reinserting the base into the tube.

While I had each unit apart, I wiped it down with a dry cloth (to remove the copper dust), and checked for water intrusion or other problems. I also checked to make sure all of the gaskets and O-rings looked good.


Disassembly and reassembly of the matching unit of the ATAS-120A is a fairly involved procedure. The unit is a sealed assembly and needs no regular repair or maintenance. Inside the matching assembly is a copper coil that connects the lower chrome portion of the assembly with the upper portion, with a few capacitors soldered from sections of the coil to the center conductor. The coil is wrapped around a plastic form, and the center conductor is hidden within this form. The outer (black) plastic shell is about 1/8" thick.

There are a few reports online that the internal coil solder connections can become cracked, so it may be of interest to open the unit up for inspection from time to time. However, use caution when doing this! It is possible that the majority of the situations of poor antenna connections are either in the antenna mount itself, or more likely in the SO-239 center conductor that mates with the PL-259 pin on the antenna. If this center conductor on the mount is bad, there is no point in disassembling the matching unit! It's also possible that the online reports of coil failure are based on early versions of the coil.

The procedure for disassembly of the matching unit from an ATAS-120A is as follows:


0. All work can be done with the top section connected to the matching unit.

1. Locate the upper and lower pins (silver) on the matching unit.

2. Using a sharp knife, cut away the plastic around the lower pin. Try to remove plastic in at most a 1/4" diameter hole around the pin. You'll have to dig down fairly deep until you hit the shiny chrome steel ring that the pin secures into.

3. Try pulling the pin straight out using needle-nose pliers. One internet report indicates this pin can be pulled out using locking needle-nose pliers, but this may be doubtful. The pin is secured into roughly 3/8" of brass below this point, it's not going to come out easy.

4. Snap the pin off at the base. This is fairly easy to do by putting the matching unit in a padded vise, and then tapping the pin in different directions with a center punch. After a few taps in each direction, the pin will snap right off. The pin is stainless steel and is very hard/brittle.

5. Use a moto-tool and a narrow (1/16") diamond bit to grind the existing 1/4" hole down into the brass, following the stainless steel pin. Using a moto-tool you can physically feel the pin (hard stainless steel) embedded in the softer outer brass, and use the pin itself as a guide. Keep the hole as narrow as possible. Stop "drilling" when you reach a depth equal to the inner diameter of the inner threaded portion of the lower brass mount (roughly 3/8"). As an alternative to grinding, you can use a drill press, but it may be very difficult to keep the drill bit centered on the stainless pin amidst the brass.

6. When you're finished, you will have a 1/4" hole drilled straight down into the inner threaded brass ring. The outer chromed brass mount will then unscrew easily from the outer black plastic housing. There is a rubber O-ring (1-1/8" diameter by 1/16" thick) that may be destroyed when you unscrew the housing. If the outer chromed brass mount does not unscrew smoothly and evenly, or if the internal PL-259 connector rotates as the outer mount is turned, you have not drilled deep enough and the outer/inner threaded sections are still connected. Do not turn any more, or you will rip the internal solder connections from the internal coil. The center PL-259 plug is NOT intended to move with respect to the upper housing, if you see it move, stop. Drill slightly deeper and try again.

7. Unscrew the lower threaded chromed brass mount.

8. Put a small notch between the upper pin and the upper chromed brass mount. The notch doesn't have to be very big, only 1/16" x 1/16" and 1/8" deep.

9. You can now pull the outer plastic housing away from the upper chromed brass mount. There is another O-ring inside; since the housing pulls straight off, the O-ring should be undamaged.

10. The internal coil is now visible for inspection and repair if necessary.

11. The lower portion of the PL-259 and the upper housing are connected with the copper coil and should have zero ohms resistance. The center pin of the PL-259 is connected to the center of the PC board and should also have zero ohms resistance (the top tube of the antenna must be removed to access the PC board).


1. In the lower chromed brass mount, drill out the hole (that originally contained the steel pin) with a #21 drill bit. Be sure the hole is straight and clean.

2. Use a #10-32 tap to put threads into the hole.

3. Put the outer plastic housing back on the upper chromed brass mount.

4. Thread the lower chromed brass mount back into the upper housing.

5. Insert a 3/4" (or longer) #10-32 allen-head screw into the lower chromed brass mount.

6. When the screw bottoms out, give an additional 1/4 turn.

7. Remove the screw. Remove the lower chromed brass mount.

8. Identify the gouge in the inner PL-259 threads from the allen screw. Carefully drill out this area roughly 1/32 inch deep, just enough to provide an area for the allen screw to seat and lock the two threaded components together.

9. Reassemble the unit and verify the allen screw seats properly and locks the two threaded units.

10. Rebuild the lower half of the outer plastic housing. I used a small metal washer, cut in a D-fashion to fit the lower lip of the housing. The cut washer can be positioned with the allen screw in place, marked, and then the housing disassembled and removed. Masking tape was then used to form a dam on the inside of the housing, and the entire area was filled with epoxy. After the epoxy set, the entire area was shaped and re-drilled for the allen screw.

11. Insert the O-rings (use new ones if necessary).

12. Reassemble the unit. Tighten the allen screw. Apply a small amount of coax-seal to weatherproof the allen screw.


  1. How much is now in the USA ATAS antenna 120A ?

    73s' HB9OAE op.maico

  2. Looks like $289.95 at HRO right now:

  3. Thank you so much for taking the time to document and provide this information. 73, WU6X

  4. Thanks very much for the excellent photos and description. Cleaning my unit and installing the SS washer made all the difference in the operation of my atnenna.

  5. Any idea how the water gets into the antenna?

  6. Main way water would get in would be through a faulty seal on top. I have always used a little bit of coax seal on the very top to further waterproof it -- so far so good.

  7. I love the antenna, unfortunately I have had 3 fail because of rain, all bought brand new. I never thought of the coax seal.

    I so much want to buy another ATAS 120A because of the simplicity of the tune, but I am also leaning toward the Tarheel II so I don't have to worry about the water thing. EHAM reviews are brutal with this Yaesu antenna but your page is building more confidence.

  8. Thanks. Great info. Mine stopped tuning. It was a cold solder joint at the circuit board to the centre conductor. Mine didn't have a boot at the top so I added some self amalgamating electrical tape. Although I rarely left it out in the rain or snow there were definite signs of moisture. I used the silicon spray and lock washers and it tunes great again. It's always been a bit finicky tuning on 6m. That's still there but it's fine otherwise. Thanks again! VE3BWP

  9. Very useful information. My ATAS-120A stopped working after nearly 4 years. Opened it as per your instructions and found out that the center conductor of the PL 259 soldering to the PCB has a dry joint. Soldered this point and it's working again like before. Your detailed information gave me courage to open and repair it. 4S7AB Kamal

  10. is it possible to run 12 volts through the motor leads to make sure the motor is working. i know that i have enough voltage coming out my ft100 as i have tested this and still the atas wont move. i have stripped and cleaned the atas120 and still nothing. could it be the circuit board.i know that i dont need to have a ground to move it only for tuning but im not bothered about that at this stage i just want it to move again. when i had it stripped i could move the threaded bar no probs so it isnt seized. HELP!!!!! plz

    1. Yes. as a mater of fact the ATAS120 I bought on EBay had a small switch assembly the previous owner built to use the antenna with a radio that did not produce the 12 volts for the auto-tune. He used an SWR meter and moved the antenna up and down by reversing the polarity of the connection tuning the antenna for lowest SWR.

  11. tnx for good information, mine quit and looks like motor is got wet rusted up. Can I put 12 volts to little motor leads an try it?
    tnx 73 Ron

  12. 12V is too much for the motor -- remember, the entire drive from the coax ranges from 8V to 12V (to determine direction). 5V, applied direct to the motor leads, is much better for testing the motor itself.

  13. thanx mate got the problem, motor is workin fine. it must be the matching unit which im now gonna try and strip wish me luck. thanx MMOWKJ

  14. Dear Sir / Madam,

    I also Atas 120 is now a separate antenna I have been in reverse order him put together. Right now if I go with the 857 ft Yeasu tune I can only downwards but he remains by turning does not come back up he just runs down. Is there a special way possible for him to assemble an adjustment or change to?
    Please if possible your comment.
    In advance my kind thanks for your kind cooperation.
    Dirk Loenen

    1. I now have same problem with ATAS 120. Goes down dor 2 meter but will not go up. I can hear the motor running. I am breaking it down to see what is the problem. Must be mechanical.

  15. Bench test the motor first, +5V and -5V; if it doesn't reverse problem is motor. Next bench test whole assembly, +8V and +12V to center coax pin; if doesn't reverse likely problem is in controller board. Good luck es 73!

  16. I posted a question a few weeks ago and finally got around and worked on the ATAS 120. I had a 9 volt battery and small test leads and made the antenna go up and down buy just going to the motor direct. Found out that when my truck was not running the voltage on my truck battery was only 11.8 volts and the antenna would not work. started truck up and 12.8 plus the antenna worked fine. So low voltage to the antenna seemed to be my biggest problem. Tnx for all the good information on this site 73 Ron KD7SU

  17. thanks for a good job. nylon guide broke and your site valuable to tear apart and repair. i found a site on u-tube that showed how to operate when out of casing. a good test before putting it back together. thanks again

  18. I just opened my ATAS 120 and cleaned the insides. I replaced the washer with a SS one and reassembled. When I hit the tune button oon the radio I could hear the motor 'wanting' to move the antenna but there was no action.

    Has anyone else had this issue? What did you do to fix it? I am going to try getting into the guts deeper than I did the first time and see if there is any corrosion inside the mechanicals.


  19. I can apply voltage in both directions and have the antenna go up and down. I turn on ATAS(HF) and try to tune. My FT-857D keeps displaying high SWR and does not attempt to tune the antenna. Anyone know what section of the FT-857 controls this antenna? I have a feeling that there is an issue inside the radio itself.

  20. With symptoms like no power to antenna, and high SWR, it sounds like more of a problem with the transceiver - antenna connection to me. Check for loose cables and connectors, short-circuits, etc.

  21. I removed part of the black plastic around the lower pin. I then attached a small vice grip to the pin and it came out with a slow rotation of the pin. Pin is .059 (1.5mm). To reuse the pin I find it impossible to re-align the holes on the outer brass and inner chrome. So next step will be to drill a new #54 (1.4mm) hole in the inner ring once reassembled. And yes the solder joint was broken at the base. Once I soldered it back the antenna worked fine. Yaesu declined to fix it but would sell me a new base for $270.00.

    73 - KF5Y

  22. Hi, I would just like to pass my thanks for a great article. My ATAS is now like new again.
    73 de M0TNG

  23. Will a longer wipe make any different in preferment’s 73s

  24. Did you take any pictures of the tuning unit disassembled? This is my third one. They all had problems. I would not buy another one. Did you ever try to drive the pin out of the matching unit with a punch? That is usually the way it is done with most machinery.

  25. Sorry, I don't have any pictures of the matching unit when it was disassembled, hopefully the text description in the post is sufficient for anyone willing to take that section apart.

    Since the pin in the matching unit is recessed into a blind hole, it's going to be difficult to drive it out with a punch -- there's no where for it to go.

    Too bad you had problems with the units. My original one is still going strong after almost a hundred thousand miles of freeway and 4-wheel driving.

  26. Cleaned up the inside of my ATAS-100 and it works but noted the antenna stops tuning when the radio says the SWR is good for the freq, but when I put a MFJ-269 on the antenna lead it shows it is quite a way off. For instance 14.225 selected and stops tuning. Checked with the 269 it says the min SWR is about 13.900. I can hit and miss with the manual tune and recheck with the 269 until I get almost a flat SWR at my desired freq. Any idea why it stops tuning the antenna before it finds the lowest SWR? Is it just trying to find something acceptable then it stops? Bob KE5KDT

  27. Haven't checked the ATAS with an external analyzer, but what you describe sounds normal. The radio will tune for acceptable SWR on the ATAS and then will stop.

    (There's a whole separate debate about whether a 1:1 SWR is better than a 1.10 SWR or even a 2:1 SWR. My opinion is that as long as the radio is able to transmit full power into the load (ie. the ATAS has reduced SWR to the point where SWR protection is not kicking in), then any further optimization of SWR is not necessary. For example, even a 2:1 SWR will result in only 0.5dB of power loss, at 4dB per S-unit, this will not be perceptible by the receiving station. The speed gained in tuning is probably more important than capturing the last watt in transmission efficiency.)

  28. I just get my atas120 instald, turn on antena start extending and stopt. After that no movement. Nex day again turn on antena goes down all avay. Now no any movement, jus can here motor spining. Wats wrong, may be you know

  29. Hard to tell what's wrong ... hopefully from all the information in the guide here, you'll be able to troubleshoot the problem yourself?

  30. I had the same problem with the atas 120 when I tried to change freq and change bands it went all the way down and stopped.

    What I found was it binds so push the tune button and go and give the outer of the antenna a slight twist not hard and mine started tuning again.

    If not successful go to the menu turn off the tune function of the ATAS and then turn off rig and then turn it back on go to menu and turn on ATAS HF / 6M and then push tune it will initate wait till it completes ans when completed try to tune again.

    It worked for me.

  31. I had same problem turn off ATAS HF/6 in menu turn on rig go to menu reenter ATAS HF/6M in menu and then push tune button to initat then wait while it configures when it stops push tune and see if it works.

    If not push tune go to antenna give light twist action to outer cover mine was binding then this worked.

    I have now given mine a spray of WD40 which I hope will stop the binding which has happen many times on my antenna.

  32. Thanks for the info on this website. 73 ON6AT

  33. I use my atas-120a as a base antenna
    Sometimes its usefull to set the rig ( yaesu ft-897D in my case) to 2 mtrs and than push the tune button. The Atas-120A will go down all the way. The next time you tune on a other band it will work without any problems.

  34. My motor is dead. (ATAS 100) Has anyone found a replacement motor and do you have instructions for the removal of the motor ? Thanks for you help. W5JBB

  35. Pretty good, but this assumes you're ABLE to get it apart. Owing to Yaesu's design of an aluminum tube against a chromed-brass lower unit, the units FREQUENTLY develop electrolytic action between the dissimilar metals and SEVERE corrosion develops. I've used numerous methods for overcoming this, but it's always a hassle to get one apart, that has never BEEN apart. I've serviced somewhere over 60 of these antennas (100's, 120's, and 120A's), and they all have similar problems relating to water and the wretched "leadless" solder in use today. i.e. the bottom lead of the lower-unit's main inductor is held ONLY by the solder (Yaesu's "solder-tab" fix is unreliable), and frequently snaps off when the solder crystallizes and breaks, due to natural vibration. The ONLY cure for this is to cut the plastic cover in two (the pins CANNOT be removed), repair the problem, and plastic-epoxy the cover back together, as it IS a structural member.

    Happy to help anybody who has a "sick" ATAS - Tom Dailey WØEAJ... look under and click on VINTAGE RADIO REPAIR. 73

  36. just took apart My atas-100 and found the top of the coil has a wire running up to the whip, found it was seperated due to corrosion any ideas on what to do about this? I thought about using solder braid and soldering it to the coil then sliding it up into the cavity of the whip. only problem is that when screwing the whip head on it will twist the braid, and you have to have the whips allen screws tightened because on the atas100 there is a rubber boot over the top of one of the screws. any ideas on this?
    also i found about a tbl spoon of water in the lower coil unit and that coil is unsoldered as well. I guess that is why they came out with the atas-120

  37. Thanks for a great article,had a sick Atas 120a,but after disassembly found problem was mechanical (thankfully?) it had uncoupled,and only a matter of re working great.Best 73, EI8DY.

  38. Can the Atas120A work with a Icom IC706MKII Radio..

    Frank VK3HLM

  39. My atas 120 works with 5 volts applied, but when connected to a 857d and tune is pressed all I get is ITIN on the LCD

    dON KD5ZBI

  40. This helped me very well, thank you so much. 73 de Philip G0ISW

  41. My atas-120 was purchased used and the whip holder drilled and screws stripped, I have ordered new holder from yeasu anyone have any info on changout? Thanks John KD0ZCO

  42. i have a atas 120 and have had problems with it not adjusting even though the motor is running.after a while of changing bands and trying to get it to tune it will suddenly start moving like normal ??? any ideas on what could couse this? thanks

  43. Absolutely brilliant article with detailed instructions and pics. The information in the Q&A also extremely helpful. Thanks so much KB5WIA
    IanB de VK3IJB (and also N3IAN)

  44. Very useful information and thanks forposting it. My problem is that I was operating my FT-857D on two meters with the ATAS-120 in the bottom position and when I switchwd to HF, the antenna did not move? I have triedeverything andcannoit get the antenna to move at all. I can hear the motor running but no results? Can you help me.
    Mike WB5PBS

  45. Hi .
    I'm from Russia.
    Random read your article at night. Antenna (ATAS 120) was in the trunk of the car - I was taking it for repairs, motor turns and the antenna does not extend.
    Plucking up courage, I have to take it apart. And lo! She earned (after a few tests, and supply 12V DC connector PL).
    Thanks you !
    If such an detailed images, and the world would become simpler and easier!