Last updated: 25 January 2004

ETX90 Motor Fault

Date: 1/24/04, 06:45
i have attached a description of the work carried out fixing a Motor
    Regards Mike Cook

I bought a used ETX90 about a year ago and at first everything seemed to work OK, later I decided to buy an Autostar, and from that time on my problems started. My main issue was a Motor Fault Detected alarm, I tried everything Calibrating , Training, New batteries, new power source, I even  removed the motors and had them tested, all to no avail still the same  Motor Fault Detected. At this point I was on the verge of giving up, but then a colleague suggested we Take the damn thing to bits and fix it.  I thought what the hell its not working correctly now so it cant do any more harm. How wrong can you be, i pulled a wire from  the circuit board to the battery compartment?


 We managed to reconnect the wire onto the raised post on the inner side of the board. We did this without any problem, but as we were testing the small circuit board where the power is fed from we noticed that if we moved the board we got some funny readings, we eventually established that there was a dry joint on the board. Now we really had problems the small circuit board had to come out. Undaunted we set about it, the first thing to  come off was the Dec lock lever it really is made out of plastic, then the long bolt was loosened carefully taking care not to damage the wires to the ALT motor passing through it, at this point we removed the wires from the plug for the power supply. Then  the Dec motor assembly was removed

This gave access to the large Declination axis lock nut this was promptly removed along with the long bolt and drive cog.  We then removed the forks from the base, but  were still unable to see the board for another plate Aha! we find 5 small screws around the perimeter which we  remove, but it still wont come  loose, then eureka the two screws on the outer of the base where the table tripod legs fit were removed and the plate

came off .

Arrow points to hard stop


The arrow points to one of the screws that need to be removed


 The arrow points to the raised post where the Battery cable was attached


 There it was one small circuit board. We still couldnt get to the fault so out came the soldering iron and all the components were removed from the board, there were cries of It will never work again, but we persevered, found the fault and replaced all the components with the much appreciated help from my colleague. At this point I carried out all the Technical enhancement tips  suggested on your website, we rebuilt the base unit refitted the forks, and motor gave it a quick test and guess what Motor Fault Detected, off came the base and as we were removing the screws that hold the motor in place the whole assembly moved to one side, several attempts were made to refit the motor but each time the screws were tightened the whole thing moved slightly so that the encoder /wheel was slightly out of alignment we eventually stopped this movement with a mall piece of packing, On went the base plate in went the batteries and the moment came to switch on, The autostar initialised and I went to set-up and align It Worked no motor fault. I refitted the OTA and attempted my first alignment, it was miles out. I heeded Mikes advice and Reset, calibrated and trained the motors, as I was training the motors I noticed that the controls for re-centring were reversed i.e. the < > keys were operating the Alt motor I removed the base again and sure enough somehow I had reverse the cables to the motor plugs, these were put right and I went for another alignment, this time everything worked fine, and I now have fully operational Scope.

I would never have attempted to carry out any of this repair had it not been for the information gleaned from Weasners Mighty ETX Site.


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