AP900 power on problem, was cold weather problem

Keith Graham <kag@...>


Would you please comment on the issue of power supply/scope power up? Is it advisable to power up the scope only after the power supply has been powered up? I had not heard of this procedure previous to this thread.


Keith Graham

Roland Christen

In a message dated 2/25/2007 2:56:51 PM Central Standard Time, kag@...

This sequence of powering on the mount AFTER turning on the power supply is
a new one on me. This is the first I have heard of this. Perhaps this is
addressed in the manual and I overlooked it. My mount is connected directly to
the power supply and turns on when the power supply is powered up. Until now,
I have never seen this as being a concern. Roland, would you mind commenting
on this? Should the power supply be turned on first, wait 30 (or so) seconds,
and then power up the mount? If this is the case, I will certainly abide
revise my power up routine.
Sorry to be entering this discussion so late. I have been out with the flu
for the last 5 days.

First, there is nothing in particular you need to do to start the mount.
Simply hook up the power leads to a power source and turn on the power. As soon as
the voltage exceeds 5 volts, the main computer becomes alive. Above 12 volts,
the motor drivers will have enough power to go at 1200x. Normally, all this
happens in less than 100 miliseconds, so it is not something that you would
notice. Whether you turn the power on from a switch or by plugging the cord into
the servo controller will make no difference. You can start the servo with the
keypad plugged in (normal operation), or you can plug the keypad in after the
servo is powered up. There is no difference in startup procedure. In either
case, the servo will begin operation the moment it gets its initialization from
the keypad (or from your external computer software).

In the CP1 and CP2 controllers there was a fault mode that could occur if the
power at startup went back to zero voltage a number of times before finally
reaching 12 volts. These zero excursions could cause the motor controllers to
continually restart and finally fail to set properly. The symptom would be a
sudden runaway of one or both motors for about 1 - 2 seconds at startup. The
motors would go at full speed and stop abruptly. Although this would be very
unsettling, no damage occurs under this unusual condition. As soon as the motors
stop, the system has actually recovered, and is ready for normal operation (no
panicky unplugging of the mount is required unless your clutches are fully
tightened and the scope seems to be heading toward the pier). The only thing that
has happened is that the mount has now lost its internal stored reference
point and will require a new "Sync" on a known object with the scope on the
opposite side of the meridian as the object. This would be the only time that a
sync is required, and is the same situation as a mount that is newly configured
for the first time.

In the CP3, the internal components are configured differently to avoid this
momentary runaway conditions. Only the older controllers have this
vulnerability. The vulnerability occurs only if these zero voltage spikes occur beyond
the first 1/2 second that you have applied power. The internal software ignores
the first 1/2 second of voltage spikes and perturbations, but if they recur
after that point, then you may get this momentary motor runaway. A faulty power
switch can produce these voltage dropouts or intermittent conditions. Another
cause is plugging the cigar connector too slowly into the receptacle, which
causes intermittent contact. One solution to either of these is to connect a
simple large electrolytic capacitor (the larger the better) across (in parallel
with) the 12 volt power cord on the servo side. This will eliminate completely
any power supply or power switch startup problems with the servo. Again, only
the CP1 and 2 have this as an issue, and it is quite a rare thing to happen
uless you have a real power switch problem.

For anyone having any unusual problems with their servo, it is always best to
contact one of us here at AP. Howard, myself and Wally have lots of
experience with helping people figure out what could possibly be wrong. It also allows
us to do some long distance analysis with the customer. This almost always
clears up the problem or suggests the next move needed to fix it. Going on this
newsgroup, asking people to trouble shoot your system may sound like the thing
to do (especially of you come from another telescope experience), but it
usually ends with speculation and lots of try this try that, which mostly don't
adress the real problem. So, call us instead, we'll help you for sure.

Roland Christen

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