Telescope Reviews: SS Autoguider testing

This may have already been posted somewhere in the various forums, but thought I'd upload it anyway.

I recently had a problem with my StarShooter autoguider and my CGEM, so I'll describe what happened and how I solved it. Hopefully, anyone with a similiar failure will find this useful. Two nights ago, I had my CGEM out trying to do a few hours of imaging on the first clear night this week. I had everything setup normally and Phd calibrated and began tracking the guide star I'd chosen. After a few minutes, I'd otherwise been busy setting up Nebulosity, it began to alert that there was low SNR and it had lost the lock on the star. I restarted Phd and began the calibration again, watching it train on the same star. Phd completed it's tracking adjustments, ending with south corrections and then the yellow lines turned green indicating that it had begun tracking. I took a preview shot to see how far I was off target and half way through the exposure, Phd began alerting again, same problem, low SNR and again, it was not following the guide star. Well, this second failure ended any hopes that night of doing any guided long exposures. I took the mount back in the house and had to wait until today to troubleshoot the problem. Turns out, that although Phd had calibrated itself and began tracking, all of the N,S, E, and W signals were not reaching the mount autoguide port. I had done some research on the web, looking for autoguider help, ST4 port information, whatever I could find to help me isolate the problem. Was it the cable, the SS guider, the mount itself? Where and how was I going to start? Much of what I'd read online, had to do with measuring voltages or resistance through the cable or building a 4 switch box with a cable that would allow you to manually activate each direction line to the mount. Both methods, and others, were time consuming and required you to build something, disassemble something, or wait until it got dark to attempt some settings adjustments in Phd itself during tracking. Well, I thought there has to be a better, easier way. And there is. Here's how to test your autoguider with Phd and the CGEM hand controller. This procedure should work with any autoguider that Phd supports and any HC software that allows you watch the RA / DEC axis readouts. So...

1. Setup your mount, autoguider and laptop. We only need the USB interface from the laptop to the autoguider, the autoguider cable running to the mount and of course the mount powered on with the hand controller attached.

2. For the CGEM, at power up, press the menu button and select Utilities, Get Axis Position. The HC display should show 90 degs for both axis, ALT / AZM. Since we have not done an alignment, both counters should be steady, neither incrementing or decrementing.

3. Start Phd and select your autoguider with the Camera icon. At the top of the autoguider window, select Tools, Manual Guide. This will display the manual output window with 4 cardinal point buttons (N, E, S and W).

4. Now were ready to test. Simply click on one of the direction buttons and observe the result on the hand controller. On my setup, you should see the ALT read out incrementing when your click on North and decrementing with you click on South. For West and East, AZM should increment and decrement. I say on my setup because there have been other pin assignments used for the various generations of autoguiders. Your setup may be different.

Watching the ALT / AZM readouts change in response to which direction button you click on will tell if one or more of the autoguider cable pins is not making contact. In my case, the line that controls -ALT was not making contact. I found the problem to be a slightly bent pin in the autoguider ST4 port itself. Granted if I had inspected the ports and cables, I probably would have seen the slight bend in the port pin without this testing, but I now have a quick and easy method to not only test Phd, but the cables and the mount autoguide interface itself. All without having to lug anything outside. Hope this helps anyone having similiar problems...AND you can test your autoguide interface in the field very quickly if you are having problems.

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C8 / EON 80 APO
CGEM / CG5
ST80 with SS AG setup
Canon 1000d

Edited by BlueGrass (10/09/09 09:32 PM)