RE: [APML] ST-4 question-UPDATE WITH NO RESOLUTION

["Lane, Jason R" <jason.lane@navy.mil>]

Hey Alan,

Hope you can get it figured out.  I've got a handful of suggestions from resolving issues when I bought my ST-4 last year that you can look into.

Well, one suggestion I don't need to make since Chris suggested a mount-related issue for #1.  Check the surface of the chip and window to make sure there's no lingering water spots left on them (good idea to check anyways.  Also, ensure the wires going to the imaging chip are not touching.  Be careful as these are delicate.  Finally, turn on your ST-4 and look for condensation inside the window after it chills down.  If there is, it's likely your O-Ring needs replacement (probably good idea since it's likely 10+ years old anyways).  You can get a good replacement out of O-Ring kits like those sold through Harbor Freight.  Oh also, what power supply are you using?  I've found my ST-4 is pretty sensitive to power supply and wears down my old spare car battery fairly quickly if I'm powering the scope as well.

Good luck!
Jason

-----Original Message-----
From: astro-photo-bounces@seds.org
[mailto:astro-photo-bounces@seds.org]On Behalf Of Alan Voetsch
Sent: Thursday, September 09, 2004 11:01 AM
To: Discussion of Film Astrophotography
Subject: [APML] ST-4 question-UPDATE WITH NO RESOLUTION


Hey all,

In an effort to end this thread before next year I thought I'd post an
update after replacing the desiccant ring. There was no improvement.
I've giver it 3 nights to see if there was any change and there isn't.
My symptoms were, and are; 

1. Guider not returning the star to the same position when calibration
was finished. It always has before.

2. Lower than normal brightness readings. I am having to use longer
exposures and higher 'boost' settings than before. I'd estimate that
the readings are about 50% lower than what they used to be. Over the
years I have gotten pretty good at guessing what parameters to use to
get a star to a certain brightness.

3. Completely losing the guidestar a couple times. Never did that
before.

4. Before starting one exposure, it was reading about '15' for
brightness. When ended, the brightness had gone up to about'40'. That
was about 2 hours later and the temperature had dropped about 10
degrees.

5. Upon power up, where the brightness reading used to drop to '10'
after a minute, it now only gets to '12'.

6. Guiding has remained OK, although I have not had any film developed
this week. A check of guidestar location before and after a 3 hour
exposure last night showed that the star was in the same location.
Focus had shifted due to falling temps, but still guidestar brightness
increased almost 50% during the exposure. This indicates to me that
improper cooling is possibly responsible for the problems during the
early evening hours.

It's possible that number #1 is mount-related as Chris Schur suggested.
My focus is still optimal.  As a precaution, I ran a piece of yarn
through and around the cooling fins as I had noticed some dust
build-up. No change. I suspect either a chip that is getting too old,
or a problem in the cooling system. I have few mechanical or electronic
skills, so I'm only guessing. I can't see how a faulty relay could be
responsible for the all of the above symptoms so I do not suspect that.
I don't know what else might cause the problems I'm seeing. 

I'm going to send an enquiry to SBIG, maybe they still do repairs, or
have some advice I can use.

Thnaks for all the suggestions,
Alan




		
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