BobKinsman

Sorry I should have said. On the first 2 images, the horizontal scale is 100ms per division, the last one 10us per division. The vertical scale is winding current for the 2 RA motor windings (DEC is basically the same). These are measured at the un-earthed end of the winding current sense resistors where they go into the appropriate driver chip ( 2 windings & chips for one motor). The peak current is about 0.5v/0.68ohms or about +/- 0.75A max. I think there are 64 micro steps per motor step, the current ramping up and down with a sinusoidal envelope over the course of 1/200 of a rev. The amplitudes and phasing of the 2 traces in the last picture varies considerably over the course of the micro-step cycle

I had a look at the currents in the stepper motors today. Using the handset buttons, they are fine at all speeds except Rate 0 and 1. At Rate 1, there are no microstepping currents in one direction only, just the holding currents that are there when no button is pressed. At Rate 0, the motor moves in the same direction whether left or right buttons are pressed !! When using PHD2 via ST4, I don't understand the East / West behaviour below, though it may be correct. The buttons referred to are those in the manual guiding window. The microstep cycle referred to is the is time to complete one motor step, through the sequence of microstep currents. A couple of pictures of this are shown below. Motor CW direction corresponds to CW rotation of scope, i.e following the stars. PHD2 manual guiding, Mount tracking off, PHD2 guide speed 0.1 x sidereal. East button, 0.8s / microstep cycle : Motor CW West button, 2.4s / microstep cycle : Motor CW ?? Same as East!! North button, 2.4s / microstep cycle : Motor CCW Southbutton, 2.4s / microstep cycle : Motor CW PHD2 manual guide, Mount tracking sidereal 0.5x, PHD2 guide speed 0.5 x sidereal No button, RA motor: 1.2s microstep cycle : Motor CW East button, 0.8s / microstep cycle : Motor CW West button, 2.4s / microstep cycle : Motor CW ?? Same as East!! No button, DEC motor: no movement & only holding current North button, 2.4s / microstep cycle : Motor CCW Southbutton, 2.4s / microstep cycle : Motor CW This is the behaviour with no scope on the mount, i.e. slight unbalanced in RA, but good in DEC. The PSU is a Maplin 13.8v 7.5A mains unit I am now not sure whether guiding should work or not. Unfortunately, we had 100% cloud last night so I couldn't try again. There is obviously an electronic fault related to Rate0 &1 on the handset or MC board, but that would not justify replacement unless it upsets EQMOD guiding at some point. Perhaps it is time to get a cable and find out.

Thanks for your replies guys. I have exactly the same setup as per your diagram Malcolm, and it worked well for a couple of evenings. Whilst I will inevitably move over to EQDIR to be able to do plate solving etc in the future, I wonder if it would address this particular problem. The motors don't run at low speed (in 3 of the 4 possible directions) no matter whether they are driven by the handset or the ST4 port. EQDIR will use the same port as the handset., so unless ASCOM / EQMOD requires the motors to run at a higher speed, I suspect the result will be the same. I think the next step is to look at the stepper motor drive voltages on an oscilloscope. That should definitively show if it is the motor controller board or something downstream. I can't imagine that both motors are faulty, so if not the MC board, it will probably be the mechanics. If that is the case, then it might be a good time to do a belt drive conversion.

Hi Malcolm, The guide camera (ASI120MM mini) connects to the mount using ST4. The PC connects to the imaging camera via USB3 and the imaging camera's usb hub connects to the guide camera via usb2. The mount has the orginal v3.23 handset, and no connection to the PC . There is no EQMOD (yet), I'm trying to keep it simple while I get the hang of PHD2, APT, etc. The mount, imaging camera and PC are powered independantly. As far as I aware, this is all working fine. The ST4 signals all get waggled in response to phd2 manual guiding commands, so I suspect it is either some swarf / sticky grease or other contaminant in the drive train, or a faulty motor control board. Bob

I have an old NEQ6 mount that I picked up secondhand last year. I've just started using it with a guide scope via ST4 and PHD2. Up until last night, it was working well with rms errors of 1 - 1.5 arc seconds. Then phd2 reported that the corrections it was making didn't seem to be having any effect. Sure enough, when I tried phd2 manual guiding this morning, the motors were silent when I pressed the east button, so I opened up the covers and watched the motors. Basically, whenever I slew at rate 0 or 1 in 3 of the 4 directions, nothing happens. Everything works fine at rate 2 or above. Unfortunately guiding appears to use rate 1, so itis not working. The signals on the ST4 connector are operating correctly and the power supply (nominally 13.8v) never falls below 13.3v, even when slewing both axes at rate 9. Does anyone have any brilliant ideas on the likely cause? I don't know whether to strip the whole thing down, or start replacing electrical bits (if available).