Tuesday, January 5, 2016

Icom IC756 PRO Antenna Tuner repair

If You are owner of any IC 74x-75x family You can experience ATU unit failure.
Crackling sound from around ATU unit, or just "no tune" state could be ATU motors malfunction.
Assuming all the radio working Okay, we can do a simple motor repair described below.

Now my neighbour Greg SQ3PBA experienced this kind of failure, so we need to help him back in bussiness ;-)

Inspiration for this article was described by MichaƂ SP2XDM doing IC-746 ATU REPAIR, but all IC's having the same ATU, or at least motors so You'll see my example at IC-756PRO.

Of course anything You'll do - bear in mind your own responsibilty if failed.

Let's start with unscrewing upper and bottom cover of the radio :

Turn it at normal position and unscrew upper shield - 11 white Phillips screws. Before removing it, remember to pull out gently the speaker connector - yellow circle on the pic.

Now You can see ATU unit on your right hand - 4 screws need to be removed first. A magnetic PH screwdriver will do the job.
Note two yellow arrows, prior to removing PCB we need to desolder SO-239 antenna connectors.

Next and last step before removing upper PCB is to remove 3 flat tape connectors pulling it up.
What we can see is another shileding cover hiding main ATU PCB.
Just 3 PH screws and we are done.

Below we will find another 4 PH screws and main ATU PCB is ready to lift up...

NOTE: Remember to set Capacitor at faulty motor to it's max capacitance. This will be needed later when mounting repaired ATU motor.

Time to remove faulty motor from chassis - use mini #PH0 screwdriver.

Now You can pull the motor backward - this was the easiest part of repair :-D

After removal look carefully at motors brake nozzle position. Best idea is to use CD pen to mark the position, or use your smartphone to make picture - even better. The brake position set any other way than it was, will not let You mount repaired motor. If this happen You'll need to use force on delicate device to move it at right position. Better avoid to do so. Let's say that Your nozzle should be the same orientation as mine on the pics. It's very close to desired position.

Now we need to open the case - be gentle with force. Use flat small screwdriver or pliers to straighten 4 case hooks.
Alternatively You can try to insert flat screwdriver vertically close to the hook and lift upper cover of the motor. Tested - it's doable ;-)

If everything is well You'll see something similar :

Carefully look at the motor, notice each satelite wheel position, best to made 5-6 pics at different angles. Gently remove each wheel, one by one, and store in safe place.

Last part we need to remove is our failed part. This is a magnetic rotator right in the middle. Pull it up and You'll see why ATU was inoperate...

It seems that the reason is material fatigue caused upper plastic ring holding magnet broke and detach from magnet.
After that ATU rotate the magnet, but not the rotor.

What we need is to repait it, using small amount of epoxy glue, or any other cyanoacrylic glue.

First degrease all parts with IPA, or any other degreasing fluid, and wipe it gently with soft cloth.

NOTE - looking inside the magnet you'll see 3 dips, where rotator should fit. Same dips are located on top. This is the place where upper plastic ring should be glued.

Apply small amount of epoxy glue on rotor, and slip magnet on it, setting his position according to dips.
Remove excessive glue (if any)with soft material and after hardening time do the same with small upper ring to secure the magnet watching for upper dips in magnet.

We are almost done. Let the epoxy solidify, and after few hours ( or minutes ) carefully examine the surface of the magnet, bottom and upper ring, remove any glue marks or dirt with sharp knife.

Now all we need is to restore the motor to it's factory state starting with repaired rotor, and cooperating wheels in reverse order.

NOTE: Before securing the cover, check orientation of the main output shaft with metal nozzle. Assure that it's almost same as on my pics. Otherwise You'll have to open the cover again, or pray not to destroy the motor turning it by hand later.

Last thing we need is to secure upper cover of the motor - screwdriver with small 100g hammer or electric pliers will do the job.

NOTE - good idea is to add small drop of machine oil, or silicon grease, but just "small" drop.
After reassembly the cover don't forget to check if brake nozzle fit in right direction as marked before.

Attach the motor to ATU chassis, put again attention that brake nozzle should is positioned as on the picture, with variable capacitor at his max capacitance (closed). Secure gently two screws on the motor clutch.

That's it. Mount the PCB inside, paying special attention to all screws and shields/cables around.

Immediately after switching radio on, You'll see motors running to last remembered position.

73 & Good luck!

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