Last updated: 3 May 2000

ETX-90RA Right Ascension Play Fix

From: George Jacob (eagle@icubed.com)

Here is the result of my experiment with the RA play on an ETX-90.

This mod can be removed easily so maybe no warranty restrictions? Maybe not since I drilled and tapped a couple of holes into the aluminum of the worm gear housing. I installed a plate of .090 aluminum bent and shaped to bear the load of the worm housing to the outside shell of the drive housing. I attached it to the worm housing by drilling very small holes and tapping them for #2-56 screws. (Use screws with the lowest head profile you can find since they rub the bottom cover). You may have to remove a little plastic from the bottom cover with a drill bit to allow the cover to flush fit. This mod removes all of the slop in the drive, but, if you watch the aluminum worm housing, it now bears all of the torque to the side arms of this housing! Those thick little rascals actually bend back and forth! Now, this was observed the same way that the problem was discovered, operating back and forth on the highest speed to observe the strain and to see "what was moving".

The driven gear should have been of a much larger diameter to decrease the load on the worm drive.

Below is a picture of the modification. Note also that depending on the size of the screw heads, you may have to remove some plastic from the bottom cover to allow a flush fit. I used a sheet metal drill bit which is a flat cut. Just place the bottom cover in place, work back and forth, and the screw heads will mark the cover. Remove only as much plastic as necessary to allow a flush fit. The bottom cover is thick and this can be done without making a hole into the battery compartment.

Anyone that wants to try this is welcome to e-mail me with questions they may have.

On the battery replacement subject, I use a 12v 6 amp hour sealed lead acid battery to run mine. This beast will last for many sessions before needing re-charged with either a simple lab supply, your auto cigarette lighter, or a wall cube.


RA fix

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