"Johan van der Walt" wrote in message
news:1126793835.929485@utl-lnx1...
I hope this is the right place to post this.


We bought a Meade LX200 (12 inch) about six years ago and at the same
time a Meade Pictor 416XT ccd camera (was never really satisfied with
it and didn't used it at all the last couple of years). Recently we
got a new ST-8 SBIG camera.

Earlier this year (in May, at the start of our winter observing
season) I mounted the SBIG camera for the first time on the telescope
to test it and to see how the software works. At some point during
the night I suggested to my friend that we connect the camera to the
telescope to test the autoguiding facilities. This implies connecting
the camera and the LX200 with a telephone-like cable. We were
following the instructions in the SBIG manual and it took a while to
go through all the preliminary steps. After finishing with that part
we used the telescope's "Go to" function to steer to an alignment
star. After having done the alignment we discovered that the
telescope simply went "dead" in the sense that it refused to respond
to instructions from the hand controller. We switched the power off,
unplugged all the cable, waited for a while, plugged in all the
cables and started the telescope again. But still it refused to
respond.

A couple of days later I took the telescope to the Meade dealer in
Johannesburg (where we bought the telescope). To make a long story
short, all the electronics + motors on the telescope had to be
replaced.

With great expectation we then started our experimentation with the
camera again a couple of weeks later. On the first night everything
went fine. On the second night, however, we encountered exactly the
same problem as before except that now only the dec drive of the
telescope went dead. I informed both SBIG and Meade about the fact
that this has now happened a second time and that there must be some
problem in the communication between the telescope and the camera
that affects the telescope. SBIG's response was excellent. Meade said
that they will replace the electronics free of charge. That's also
good. However, I could not get an answer from Meade about what a
possible cause for the problem might be - after returning the main
electronics board to Meade.

Problem is that I still don't know what is the cause of the problem.
Our electronics engineer strongly suggested that it might be static
electricity. Also, on SBIG's suggestion I measured the electric
potential difference between the camera and the telescope when the
camera is mounted on the telescope and when it is not. In both cases
I found that the camera's body (an electrical ground) is about 2.5V
above that of the telescope. Furthermore, from measuring the
electrical resistance between the camera body and the telescope it
seems as if the two cannot be at a common ground - the resistance is
a couple mega ohm. Our electronics guy's hypothesis is that in this
case one may easily raise the camera's electric potential to a 100 V
or more through static electricity without knowing it. This may then
have a severe negative effect on the electronics of the telescope
when the camera and the telescope are connected with the
telephone-like cable. During our winter the humidity drops
significantly.

Is there anyone out there that perhaps had a similar problem?!!!
SBIG said that they never heard of this sort of problem before but
supplied us (free of charge) of a relay adapter box that might
prevent this sort of problem next time.


Is there anyone that has any idea of whether the static electricity
hypothesis might be right?? Surely there are many owners of Meade
LX200's using SBIG cameras that also live in areas where static
electricity might be a problem.
From the 'timescale', this is presumably a LX200 'classic', rather than
the GPS. There is a famous problem with these, which also applies when
using a computer connected to the serial port. The 'ground' rail supplied
on these connectors, does not connect to the power supply ground, but
instead to the top of a large resistor inside the scope, used to sense the
current flowing into the scope. If both the scope, and computer, or scope
and camera, are connected to a grounded supply, the entire supply current
for the scope will try to bypass this resistor, through the ground
connection on the accessory. Normally this destroys the accessory, rather
than the scope motors, but it sounds as if this might be your problem. The
relay box would prevent this, by providing complete isolation between the
camera and scope. Normally, the power supply used for the scope is not
grounded, and this is not then a problem.
There is a seperate comment though. _None_ of these connectors are
designed to 'hot swap'. Your description sounds as if the scope was up and
running when the connection was made, and this can easily destroy the
input electronics since there is no guarantee of the order in which the
signals connect.

Best Wishes