Loosing USB connection all the time

[lukepower]

Hello,

 

I noticed today how sensitive my mount/scope combination is regarding balancing. It worked quite well for a few hours, but then there was simply no way to use it. I tried to rebalance it, and it was damn close to perfect, but still I kept loosing the connection. Please note that the tracking (or slewing) continued even without USB connection, so it wasn't a power failure, and I could guess that the balance is not the issue here.

It could be a USB cable issue, even if I use right now a shielded one with an industrial USB hub in front of the scope (and all other accessories working well even during the interruption, like the CCD camera). Maybe it has something to do with the interface to the mount (which I hope is not the case, as I am not really willing to unmount everything to send in the mount ).

 

As for the errors, sometimes i get ReadInt errors, sometimes I loose one axis, but most often Autoslew starts to do the Software USB Unplug/Plug procedure, mostly without success.

 

Any ideas?

 

Thanks

[lukepower]

Roger,

 

I will take a picture and put it here so you can look at it. To me, it seems that part of the PCB got burnt like under short-circuit or similar. Maybe with time, the current spikes kept on damaging it more and more, till th epoint that it wasn't running anymore.

I have confidence that the guys at ASA will be able to fix it and that they have enough understanding of electronics (which I don't) to make it work reliabily. 

[lukepower]

Alright, enjoy:

 

Especially on the top and bottom there are quite some smoked components...

[Waldemar]

Good news, bad news... glad you found something, makes it a bit easier to handle. Not enjoyable though

The lead that is powering the hub (black/red) seems to come from that area. So your idea that the voltage regulator is the burned component

is probably true. It looks like a capacitor or a zener diode is fried as well, which may be the initiator to the problem.

This would really explain your connectivity problems.

It is hard to believe this is caused by a voltage drop because of high power demands from your motors.

A drop from 24 V to

With that in mind, it would be nice to see how your 24V supply tries to compensate for huge drops... maybe it overshoots the VR's limit.

 

Anyway, a new board will work wonders.

Waldemar

[lukepower]

Hi Waldemar,

 

my personal guess is two-fold:

• First, we had a very stron thunderstorm last summer, when a lighting struck a construction crane at our neighbour (about 20 meters from the observatory). We only had a few power units of some security cameras that got burnt (mostly capacitors), but others had broken TVs and so on. Might well be a cause of the defect
• Second, the mount was off since may 2013 till beginning of december, when we got the new OTA. During the first test, there was something smelly around the mount, but it kept on working and it disappeared, so I didn't care.

 

SO, my guess would be that the lightning ruined the capacitor and/or the voltage regulator. All other problems might well be the result of that event...

[Roger]

Insulation breakdown (insulation in the widest sense, oxide layers in semiconductors), ie static damage, could readily give rise to a runaway situation such as this.  Thanks for sharing.

[lukepower]

Let's see when ASA will get this stuff picked up, I am eagerly waiting for this. Of course, now the weather would be great, no clouds in sight for quite a few days

[gmalits]

Hi Lukas,

 

this PCB ist the focuser-Controller, do you use this buit in feature ?.

If not, disconnect it, and give the mount a try. 

[lukepower]

Hi Gerald,

 

well, no, I actually got an external controller for that (still not used, though). Gerald, do you know if I could somehow have a look at the controller card of the motors? I wonder if this defect propagated also to the remaining electronics and/or this defect interferes with the correct working of the remaining of the mount...

[gmalits]

Hi Lukas,

 

sorry, i have never seen the mounts inside live ... but why dont give it a try by unpluging the burned pcb, if you dont need it.

pull off the 2-line powercord and the usb-cable ...

[nakbrooks]

Personally if it were my one I'd be worried about invalidating the warranty by doing too much DIY surgery. I'd leave it to ASA to sort out. Just a thought.

[lukepower]

Gerald, I already unmounted everything and put it in the shipment boxes, so right now I'll just wait for ASA to send UPS to get them.

I actually hoped that the burned PCB would bethe one for the DEC motors, at least it would all make sense easily. Well, let's wait and hope

[Waldemar]

Any progress, Lukas?

[lukepower]

Hi Waldemar,

 

not really, ASA got the mount and confirmed that the PCB of the focuser controller burned away - however, the problems should not come from there they said. I never needed or used it anyway, btw.

 

So, just waiting to see what happens...

[Roger]

If the troubles originally started following a  lightning zap there could be latent damage on any pcb sadly.

[lukepower]

Let's see, I am confident ASA will find and resolve the problem. Hopefully there is one, of course

[TimC]

Hi,

 

I think I have been having a similar problem where the DDM85 works OK for 20 to 60 minutes then just freezes up randomly. I will send the logs to ASA to see if they can help diagnose the problem. ASA did check the tuning recently. It may be a balance issue, but it I have tried re-balancing many times.

 

Regards,

Tim

[lukepower]

Hi Tim,

 

what do you mean by "freezes up"? Does the mount stop running, or does Autoslew report it had lost the connection to the mount? Might be interesting to see if there are identical components in both of our setups, maybe the fault lies somewhere else (USB hub, power, mainboard...)...

[MarkS]

Hi,

 

I think I have been having a similar problem where the DDM85 works OK for 20 to 60 minutes then just freezes up randomly. I will send the logs to ASA to see if they can help diagnose the problem. ASA did check the tuning recently. It may be a balance issue, but it I have tried re-balancing many times.

 

Regards,

Tim

Hi Tim,

 

Does AS report a "Position Error" when  the DDM85 freezes? If not, ignore the following

 

If so, it may be worth putting an ammeter in the DDM power supply lead to track the motor current. With my DDM60 it will always show increasing current when a position error is imminent. I have found the only infallible way to optimise Balance is to minimise motor current over long tracking times.

 

I always set up with the Balance Tool, but it doesn't always guarantee trouble free running over long periods.

 

Also, when I use Sequence Run to set up a long session, I always program a relaxation slew and re-focus every hour or so, which 'resets' the motor currents to low values. It's just a precaution but I find it is good insurance against problems if I haven't nailed the balance - which I have to re-establish every session on my mobile set-up. 

 

Regards,

Mark

[TimC]

Hi,

 

Thanks very much. Yes, I do see position errors -  taken from recent logs......

 

04:49:14.625: Interface SlewToTargetAsynch
04:49:14.625: Interface setting TargetRightAscension to 16.11 True
04:49:14.640: Interface setting TargetDeclination to -44.08 True
04:49:14.640: Interface SlewToTargetAsynch
04:49:14.859: Interface SetPark with Az=179.6 Alt=28.0
04:49:15.062: Interface Park
04:49:15.062: Starting Slew to RA 16.12h  DE -79.08d  EPOCH 0000
04:49:28.734: Telescope Interface sets Tracking to False
04:53:28.796: Raising fatal Error RA Axis: Position Error

 

01:42:21.140: Starting Slew to RA 11.42h  DE -23.26d  EPOCH 0000
01:42:32.156: Raising Warning DE Axis: Position Error
Position Error during slewing autocorrected by ClServo
Position Error correction failed

01:42:38.093: Raising Warning DE Axis: Position Error
Position Error correction failed

01:42:46.062: Raising Warning DE Axis: Position Error
Position Error correction failed

01:42:57.187: Raising Fatal Error DE Axis: Position Error
Position Error correction failed
 

 

01:42:21.312: Axis 1 slewing to 14.01
01:42:21.375: Axis 2 slewing to 23.51
01:42:22.250: Axis 2 Pos:+004.01° Curr:+02.3A PosErr:+08.54arcsec
01:42:22.921: Axis 1 Pos:+014.06° Curr:+01.0A PosErr:+02.85arcsec
01:42:28.406: Axis 2 Pos:+017.92° Curr:+02.1A PosErr:+10.25arcsec
01:42:29.078: Axis 1 Pos:+014.01° Curr:+00.9A PosErr:-00.96arcsec
01:42:30.500: Axis 2 Error: Position Error
01:42:30.859: Axis 2 trying to autocorrect error and slewing again to 23.51
01:42:31.953: Axis 2 autocorrect slewing error failed
01:42:32.203: Axis 2 Error: Position Error
01:42:32.234: Axis 2 Error: Velocity Limit Exceeded
01:42:32.250: Axis 22 Tracking errors within 60 seconds, giving up
01:42:33.234: Axis 2 Error: Velocity Limit Exceeded
01:42:34.328: Axis 2 Error: Velocity Limit Exceeded
01:42:34.375: Axis 2 Pos:-004.23° Curr:+00.0A PosErr:+02.49arcsec
01:42:34.656: Axis 2 Error Cleared
01:42:34.671: Axis 2 turned off Motor
01:42:34.718: Axis 2 turned on Motor
01:42:35.343: Axis 1 Pos:+014.02° Curr:+00.1A PosErr:-00.54arcsec
01:42:35.390: Axis 2 Error: Position Error
01:42:35.406: Axis 2 Error: Velocity Limit Exceeded
01:42:35.437: Axis 2 trying to autocorrect tracking error
01:42:37.937: Axis 2 Error: Position Error
01:42:37.968: Axis 2 Error: Velocity Limit Exceeded
01:42:37.984: Axis 22 Tracking errors within 60 seconds, giving up
01:42:38.984: Axis 2 Error: Velocity Limit Exceeded
01:42:40.093: Axis 2 Pos:-029.28° Curr:+00.0A PosErr:+00.00arcsec
01:42:40.593: Axis 2 Error Cleared
01:42:40.593: Axis 2 turned off Motor
01:42:40.781: Axis 2 turned on Motor
01:42:41.125: Axis 1 Pos:+014.03° Curr:+00.2A PosErr:-01.79arcsec
01:42:43.296: Axis 2 Error: Position Error
01:42:43.328: Axis 2 trying to autocorrect tracking error
01:42:45.859: Axis 2 Error: Position Error
01:42:45.890: Axis 2 Error: Velocity Limit Exceeded
01:42:45.906: Axis 22 Tracking errors within 60 seconds, giving up
01:42:45.937: Axis 2 Pos:-024.28° Curr:+00.0A PosErr:+02.57arcsec
01:42:46.953: Axis 1 Pos:+014.04° Curr:+00.4A PosErr:-00.32arcsec
01:42:48.562: Axis 2 Error Cleared
01:42:48.562: Axis 2 turned off Motor
01:42:48.625: Axis 2 turned on Motor
01:42:52.328: Axis 2 Pos:-028.48° Curr:+03.2A PosErr:-04.02arcsec
01:42:53.406: Axis 1 Pos:+014.06° Curr:+00.2A PosErr:-00.18arcsec
01:42:53.437: Axis 2 Error: Position Error
01:42:53.453: Axis 2 trying to autocorrect tracking error
01:42:57.031: Axis 2 Error: Position Error
01:42:57.062: Axis 2 Error: Velocity Limit Exceeded
01:42:57.078: Axis 22 Tracking errors within 60 seconds, giving up

 

With a fixed setup in a remote location with unattended robotic operation all night long, I hope there will be a way to balance and tune the system so that these don't occur at all. I just hope there is only operator insufficiency involved and not a problem with the mount itself.

 

Mark, this is a worry to me....."I always set up with the Balance Tool, but it doesn't always guarantee trouble free running over long periods."....

 

ASA are going to remote in again to see if the tuning can be improved. I will work harder on the balance issue...but...I have an asymmetric camera filter wheel off axis guider combination  with a camera rotator that rotates this whole assembly all over the place to get a guide star at focal length 4.7m. I can look at attaching a counter weight to the assembly, but it will be hard to assess the balance of the counterweight against the imaging devices.

 

Regards,

Tim

[lukepower]

Hi Tim,

 

my first though would also be the balance. My setup is quite heavy (around 100kg), and my camera is also slightly asymmetric (well, the filter wheel is). Small changes can help alot, so try to get rid of everything moving the center of weight/gravity away from the mechanical center of the tube. In my case, I had a small mounting plate on one side of the scope. Removing it helped alot, even if it was not really visible in the balance tool. 

 

Two more things: The PID values can make a huge difference, and so do the acceleration/speed values which you can also set (lower) in Autoslew. May I ask what kind of OTA you have on your mount?

[TimC]

Thanks Lukas,

 

I have a  Philipp Keller 20 inch Classical Cassegrain  ( very similar, but I believe heavier than the ASA version) which is a very heavy scope. Attached is a FLI PL16803 plus FLI filterwheel and a MegaMOAG off axis guider with a ST402 autoguider....quite a heavy payload, I'm afraid.

 

Regards,

Tim

[lukepower]

Hi Tim,

 

well, kind of similar to my setup. Do you have the normal DDM85 or the heavy version DDM85XL?

What I can say is that balancing is crucial and difficult at the same time (regrettably). Try to remove the imaging train and work once just with visual accessories, so that you have no asymmetry in the tube. Then try to center the center of gravity of the tube exactly on the axis of the mount. If you do it right (=damn good), the errors should resolve. It might help to reduce the acceleration values in Autoslew (somewhere under Servo or Motors, if I remember correctly). I had some problems with radial unbalanced weight (like the plate I mentioned, or my OK3Z focuser, sitting on one side of the tube). It might be really difficult to get a good balance, and more than that, the acceleration/deceleration also varies depending on the position of the weights. In my situation it helped to add some weights on-axis (strange)...

[lukepower]

I just wanted to give you a small update about my problem. The guys at ASA are doing a great job, they checked the wiring and electronics and it looks like the PCB of the focuser (which I don't need) is gone, and also the integrated USB hub was defective. It seems that the errors came from there, as it was disrupting the voltage levels of the electronics.

[TimC]

Hi,

 

I have the Premium , the DDM85XL with the bent pier. ASA have confirmed that with my many balancing attempts that the balance is way off.....therefore operator error fortunately seems to be the issue....I will work hard again on the balancing!

 

Regards,

Tim

[lukepower]

Hi Tim,

 

welcome to the club I must admit that an easier way to perfectly balance the beast would be very appreciated