STX guider and MyT

Discussion in 'STX and STXL Series Cameras' started by blackdragon72, Sep 29, 2020.

  1. blackdragon72

    blackdragon72 Standard User

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    I am having some weird guiding issues with my setup: STXL16803+STX guider+MyT, guiding with PHD2.

    Auto guiding works fine when guiding using SkyX ASCOM driver.
    But when I switch to auto guide port on MyT, guide star drifts to West continuously. With the help from SB forum, I identified the issue, basically it seems that the mount keeps getting guiding pulse when auto guider cable is connected. But I can not figure out how this happens, camera/mount/cable is new, I dont see obvious issue.

    I use Reverse RJ12 cable per Paramount user manual:
    1. This RJ12 port is based on pinouts from the standard SBIG guider connector used by virtually every astronomical camera with guider relays. Appendix B of the SG-4 Autoguider Operating Manual defines these guider port specifications. This operating manual is presently available from the Downloads tab of the SG-4 Autoguider web page on the Diffraction Limited website. Note that lead 5 on the Camera Port and lead 2 on the Guider Port in Figure 33 is ground.
    Calibration and guiding is working otherwise.

    What could be the reason? The star drifts as long as the cable is connected, even PHD2 is not guiding.
     
  2. Colin Haig

    Colin Haig Staff Member

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    Hmmm...
    This sounds like a miswiring or hardware electrical problem, where ground is being applied to the West (X+) direction.
    The most common cause is when people use a straight-through cable instead of a flipped cable.
    You say you have a "Reverse" cable.
    The correct cable SBIG Telescope Interface Cable would be the telephone style, flipped cable, as shown in the left side of this picture.
    Autoguidercable2.png
    What happens if no software is running? Can you stick an eyepiece in the scope and see if it i drifting at faster than the sidereal rate?
     
  3. Doug

    Doug Staff Member

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    Continuous drift is the usual symptom of having the cable pins swapped.

    One thing to note: some manufacturers have built equipment with the connectors backwards. Check the manual and see if it lines up with the SBIG manual.
     
  4. blackdragon72

    blackdragon72 Standard User

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    Colin/Doug,

    "Reverse" is the cable on the left side, so cable is correct.

    No software means no guiding software open? or open PHD2 but no guiding?

    A couple of more notes:
    - I dont think it is miswiring wire. I eyeballed wire the order looks correct. The PHD2 calibration looks same via ASCOM or via guider port, except that there is noticeable drift to west.
    - RA guiding works as "expected", PHD2 could keep up RA drift. It would have been perfect if there was no drift.
    So it looks like guide pulse is sent to scope correctly when there is a correction. But when there is no correction needed, there is an "offset" to RA continuously.
     
  5. Doug

    Doug Staff Member

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    Pull the cable out and see if you still get a drift. If so, you've got sidereal tracking set to the wrong rate somehow (or your PEC programming is wacko).
     
  6. blackdragon72

    blackdragon72 Standard User

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    No cable no drift. But I can not figure out where it is from. Could it be from guide port of STX16803, or maybe cross talk of the guide cable?
     
  7. blackdragon72

    blackdragon72 Standard User

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    Screen Shot 2020-09-30 at 3.45.20 PM.png
    When star drifts West (ie, mount tracks slower than sidereal), does it mean pin 1 is "high" continuously? or pin4?
     
  8. Doug

    Doug Staff Member

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    If the cable is reversed, the Ground (5) gets connected to +DEC (2).

    That said, some mounts have the axes scrambled up, so it's not guaranteed to be +DEC.

    The STX's guide port has an optoisolator on it, so it's not likely to be causing a problem at the telescope end.
     
  9. blackdragon72

    blackdragon72 Standard User

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    Doug,

    What does drifting west mean on guide port? Is it +RA or -RA, is is pulse signal active high or active low?
    Paramount user manual states that it is reverse order. I could confirm that the ordering is good as guiding via ASCOM is same as guiding via guide port, except drifting. If wiring is messed up inside mount then PHD2 guiding would be different via ASCOM vs guide port.
     
  10. blackdragon72

    blackdragon72 Standard User

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    Or another question. Do you think this can be caused by STX guider ASCOM driver? The driver comes from SGPro.
     
  11. Doug

    Doug Staff Member

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    Well since it's often called the "ST-4 Interface", I'd hope that SBIG has the pins in the right order, not the other guys. ;)

    I don't think it's caused the the ASCOM driver. I don't know what it's caused by!

    Suggestion: since you're using a Paramount, skip the guide cable and use PulseGuide via the TheSky ASCOM driver.
     
  12. blackdragon72

    blackdragon72 Standard User

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    ASCOM guiding is working fine. I am trying guide port to make sure everything is working properly, some real issue might be hidden behind it.
     
  13. blackdragon72

    blackdragon72 Standard User

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    My question remains as it will help me debug issue.

    What does drifting west mean on guide port? Is it +RA or -RA, is is pulse signal active high or active low?
     
  14. Doug

    Doug Staff Member

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    Active low.

    +/- depends on the mount manufacturer.
     
  15. Colin Haig

    Colin Haig Staff Member

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    Guide port direction inputs on the X or RA axis are usually implemented something like the following:
    Assumptions:
    1x sidereal tracking rate
    1x guide rate
    Mount already tracking sidereally (not parked, already done a goto to a star along the celestial equator for easy math).
    Mount on normal side of pier, counterweights down. (Not pier flipped).
    Guide East = Hold -X or -RA pin LOW (ground) will stop RA motion. (1x rate - 1x guiding pulse to the east = 0).
    RA motor will stop running - won't move the mount along with the earth's rotation.
    Guide West = Hold +X or +RA pin low (ground) will double RA motion (1x rate + 1x guiding pulse to the west = 2x).

    If your guide rate is 0.5x or less, then the same math applies, just the motor speed will slow or speed up.

    You could make a cable with an RJ12 on one end and bare wires on the other, and test this manually by shorting the +RA to GND for example.
    Then you'd also know if you had a hardware problem, like a bent pin in the RJ12 jack on the mount, or damaged electronics.

    If you have the RA/DEC coordinate display in TheSky X, you can watch the mount coordinates and see what happens when you do this.

    Another thing you could do is build a little circuit with an LED, 1k resistor, and 3V battery, and have the output of the guide port turn on the LED.
    e.g.
    --------- (+RA) ------ /\/\/\/\ resistor -------(|<)-- LED---- + terminal on 3V battery
    --------- (GND) -------------------------------------------------------- battery - terminal
     
  16. blackdragon72

    blackdragon72 Standard User

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    Colin,

    If star drifts West, that means the mount tracks too slow, in another word, mount gets stalled when not supposed to. So it it means that -RA (pin4) is somehow messed up. Since signal is active low, and pin4 is next to pin 5 (Ground), could this be crosstalk, static, or bent pin?
     
  17. Colin Haig

    Colin Haig Staff Member

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    So if the star is drifting west, then the RA motor isn't running fast enough. It's not stalled unless the guide rate is 1x exactly.
    I'm not sure of the sense of -RA in the Paramount - it's been a few years, and my club's mount isn't handy.
    I am assuming it is being held low.
    Usually it requires a solid ground connection. So, bent pin, or short in the cable.
     
  18. Colin Haig

    Colin Haig Staff Member

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    One other thought - since it's a MyT, there could be a problem between the RJ12 Guider jack in the MyT Instrument Panel under the versaplate down to the MKS5000 control board.
    I'd do the wire test.
     
  19. blackdragon72

    blackdragon72 Standard User

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    1. Wiring problem inside MyT would require no auto guider cable plugging into instrument panel port
    2. Bent pin in MyT instrument panel port or short cable need auto guider cable plugging into the port, but not SBIG camera
    3. Bent pin in SBIG camera or beyond would require guider cable plugging into both instrument panel and SBIG camera guide port.

    If so #1 is ruled out, no cable no drift.
    I can test #2. It is unlikely a cable issue as I tested 2 cables.
     
  20. Colin Haig

    Colin Haig Staff Member

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    One other thought - sometimes the gold wires in the jacks get misaligned, and when the plug is inserted, they may touch if not staying in their black plastic guides. Kinda like teeth on a comb, with the gold wires being separated by the teeth.
     

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