Weird Tracking Port issues with a ST8-XME

I was doing autoguide tests with a ST8-XME to try and tune my setup. I noticed a strange thing immediately. I connected cables, ST4 one and turned on mount (I tried with a Celestron CG5 and a Vixen SXD). Suddenly mount start moving full speed for few seconds then stopped. After that it starts moving like it was receiving autoguide pulses but I haven't turned on camera yet!

When turned on camera mount continues to move and it is responsive to pulses but not on -Y. I checked all cables with a tester and they seemed ok. Relays leds inside camera lights on ok when relay direction button are pressed, I used Software Bisque The Sky and CCDSoft for testing.

My fear is a fault tracking port ...

 

Sounds more likely you are using an ST4 cable with the wrong cable pinout sequence, there are two common variants of the cable, one version has the ST4 cable plug wiring sequence end-to-end using pin 1 to pin 1 .... pin 6 to pin 6, while the other version is a " changeover" cable where pin 1 at one end of the cable goes to pin 6 at the other. if you have the wrong cable then usually -y does not work, you need to ensure you use a cable that matches the camera ST4 pinouts to the mount ST4 pinouts. Good news is that using the wrong cable does not (usually) result in damage.

Connecting the ST4 cable between some cameras and mount while the camera is unpowered sends autoguide commands continually to the mount, this just depends on the camera and I can't comment on the ST8-XME as I don't have one but this is not uncommon. How the mount reacts to this varies from one mount to another, some will move both axis, some only one while others do nothing.

Check your ST4 cable end-to-end pinout sequence is correct for your mount and only connect the ST4 cable with the camera powered up, hopefully this will resolve the problem.

In an automated observatory using ST4 cable guiding the guide camera should always be powered up before the mount is powered up and the mount powered down before the guide camera at shut down to avoid the possiblity of an uncontrolled collision of the mount/telescope/camera due to the possibilty of ST4 port drive signals from the unpowered guide camera driving the mount into collision.

HTH.

William.

 

Thanks for the answer. Cables I tried have correct pinout. I asked to support forum to have confirmation also.

I tried even with a battery pack for the mount and disconnect camera totally from the plug. Same weird behavior ...
If I turn on camera I have the same pulse sent continuously to the mount ...

 

In that case, make up a small test cable and measure resistance, the camera guider port does not produce a voltage but rather closes a "relay" contact using a common from the mount .

With no guide camera signals being generated, camera not plugged into USB (or serial etc) and just the camera plugged in to power there should be high resistance between pin 2 of the cable going to the mount guide port and each of pins 3,4,5 and 6. In this state no guide correction signals are being sent to the mount. If you measure a low resistance between pin 2 and any of pins 3 to 6 that would indicate a fault with the camera guide port interface.

Test with the meter leads both forward and reversed, early cameras used real relays that would show the same resistance irrespective which way round the test leads were used, newer cameras use open collector transistors, these will show a low resistance with the test leads connected one way round and a high resistance when reversed. The important thing is that measuring between pin 2 and pins 3,4,5 and 6 the resistance is the same for all with either test lead orientation.

You can test using a multimeter on ohms range. I use a small battery powered box using LED's that I connect to the guide port cable when I am testing for this type of fault, just 4 LED's, a six pin socket and an AA battery, using pin 2 = common and pins 3,4,5 and 6 to the LEDS with a 1k ohm series resistor , the battery soldered in series without a switch. Any active output on the guider cable lights one of the LED's.

With the camera connected and operational If you are using the Sky X there is a display in the guiding tab that shows if any of the guide signals are currently active in software, without guiding there should be no activity, in this state if any one of the pins 3,4,5 or 6 are low resistance when measured against pin 2 that again confirms that the camera guide port is defective

Page 69 and 70 of the manual for the ST8 XE details the pinouts for the guiding port and TIC-78 cable.

http://diffractionlimited.com/wp-content/uploads/2016/03/USBmanRev14.pdf

 

In case of a faulty guide port do you think SBIG/Diffraction Limited could fix sending camera to them?

 

If you remember we discussed about the necessary pinouts:

http://forum.diffractionlimited.com/index.php?posts/17642/

I tried however with an inverted cable and I have same symptoms with mount moving with camera turned off.

Is it possible that I have some ground issues with both mounts so an opto isolator or relay box is needed?

 

It seems you are describing two separate problems and can you clarify the following:

1: With the camera powered on does the mount behave normally and react to drive commands with the ST4 cable connected either forwards or reversed.
With the camera powered on and the ST4 cable connected with normal pin-to-pin sequence the mount should react to drive commands in all directions only when commanded.
With the camera powered on and the ST4 cable connected with reversed pin-to-pin sequence the mount will drive in in one direction all the time without command while the other axis may not respond.

2: With the camera powered off and the ST4 cable connected with either forward or reversed pin-to-pin sequence the mount may move in one or more axis without command, if so, this may be normal behaviour and is not a fault.
If the ST8-XME uses "Open Collector" transistor switches for the guide port to send the guide pulses to the mount then with the camera powered off these switches become permananently enabled and the mount will move continually.

This is a property of many guide cameras and not limited to SBIG cameras and is a reason many people use direct guide or pulse guide via software to the mount rather than the ST4 cable. The Sky X supports both direct guide and pulse guide to the mount so if you have computer control of the mount via a laptop or PC it may be better for you to use this method of guiding and not the ST4 cable.

To progress with the ST4 cable problem first verify that guiding works correctly in all axis with the camera powered on so that you know definitely that the pin-to-pin sequence of the cable is correct. Once you know this is working then the issue of uncommanded movement with the camera powered off can be looked at.

 

1. With Camera turned on and cable with same pin layout on both plugs mounts responds only to -Y, -X referring The Sky X relay buttons. But if i press -X mount start to move continuously like it receives uninterrupted pulse sequences.

I didn't try the reverse pin layout with turned on camera because i am afraid to damage mount/camera. According to Celestron documentation Pin 1 has +5v DC output so I don't think it's safe to do it.

2. Ok. Testing with camera turned off isn't too correct at the end so I avoid to do it anymore.

CG5 can pulse guide so i gonna try this method. My only concern is not having a damaged camera.

 

I think this is a wise precaution.

If it may be of use I have attached a connection image for the ST8 with the CG5 and SXD, I believe you were making up your own cable, if so compare your wiring against the image below.
I have checked this against the manual for the CG5, the SXD and the ST8 and taken care that is is correct but I cannot guarantee it is error free so double check the diagram with your own information rather than follow it it blind.
The cable colours are from the TIC-78 layout but if you use your own cable the colours can be anything you choose.
The image shows the back of the female DB9 cable plug (wire/solder side) that is connected to the camera, to the back of the RJ12/6 plug that is connected to the mount.

Pin 1 of the RJ12/6 connector should not be used and remains disconnected, this is the +5V supply from the mount and is not needed, only pins 2 to 6 of the RJ12/6 are connected.

 

Thanks a lot for the infos. I used cables wired in that way, not by me, i buyed them but are ok because i checked with a cable tester.

What happens to me, for example, with a Sphinx SXD is this:

https://groups.yahoo.com/neo/groups/Vixen_Sphinx/conversations/messages/7490

 

Starbook has same connection as CG5 (only direction changes) ...