DVR EHU Rebuild

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One of the tapes in the Driven element Element Housing Unit (DVR EHU) had jumped the sprocket which prompted the antenna to fail when it was 2 elements. The EHU also had a good sized hole in the top of the housing, which presumably was created by a woodpecker or large bird.

On first inspection, the EHU looked OK other than minor bends in the top copper tape and some pieces of grass. There was no water or moisture inside the EHU when it was opened.

Photo 1 – DRV EHU before rebuild

I removed the tape spools and tested the EHU. At that time I noticed corrosion around the top of the motor. The motor tested fine as you can see in the video below.

Video 1 – Testing the motor in the DRV EHU

After testing the EHU, the base plate was removed. Other than the hole in the top of the EHU, the housing and balun looked good. I blew out all the grass and other debris with canned air.

Photo 2 – DRV EHU with base plate removed

A closer inspection of the motor showed severe corrosion on the outside. I turned the motor shaft by hand and compared it with two other motors and it did not feel smooth. I decided at that point not to reuse this motor.

Photo 3 – Evidence of water damage on motor
Photo 4 – Extreme corrosion on motor

The motor was replaced with a spare. The sprocket connected to the spare motor was held in place by a pin instead of the newer-style method of a screw and nut. This caused the sprocket to be loose and wobble when turned. The plan was to put the original sprocket with the screw and nut onto the spare motor. I first had to remove the pin holding the sprocket to the spare motor shaft. I tried tapping the pin out but it wouldn’t come out so it was drilled out.

Photo 5 – Sprocket shaft with older style pin to connect to motor
Photo 6 – Pin extracted by drilling to remove sprocket shaft from motor

Once the sprocket was installed on the replacement motor, the next step was to install the motor onto the base plate and solder the wires into the connector board.

Photo 7 – Replacement motor on left, old corroded motor on right
Photo 8 – Replacement stepper motor and connector board

Sticky tape was used to secure the wires to the base plate.

Photo 9 – Sticky tape used to hold wires to base plate

The base plate assembly is now complete.

Photo 10 – Completed base assembly

Before re-installing the base plate into the shell, the hole in the top of the shell needed to be repaired. In order to determine the best way to repair the hole, I had tested various methods on a damaged shell I had kept (the shell damaged in Hurricane Isaac in 2012 that prompted me to convert this antenna to 2 elements in the first place).More

A penny and JB Weld were used to repair the hole in the top of the EHU. I first sanded the top of the EHU to allow the JB Weld to adhere to the surface.

Photo 11 – Area around the hole prepared by sanding

A penny was then super-glued over the hole and let sit for several hours.

Photo 12 – Penny super-glued over the hole in the EHU

After the super glue set, JB Weld was then used to cover the penny and allowed to set overnight.

Photo 13 – JB Weld covering the penny

After the JB Weld set for 24 hours, JB Weld was also used on the inside. I didn’t want the surface of the penny to be exposed so it wouldn’t corrode.

Photo 14 – JB Weld applied on the inside of the EHU to cover the exposed penny

After the JB Weld inside the EHU set for 24 hours, I tested to make sure there was enough clearance for the motor. I put a small dab of Elmer’s glue on top of the JB Weld then set the base plate assembly into EHU temporarily to see if there was any Elmer’s glue on the motor. There wasn’t. The base plate assembly sat correctly in the EHU. The hole in the EHU was now repaired.