Re: [APML] ST-4 question

[KGKIRKLEY@aol.com]

In a message dated 7/8/02 8:45:22 PM, jeffstak@yahoo.com writes:

>Up until last month I guided thru a Tak FS-78 @ f/8.
>It was pretty easy going with no strange behavior. In
>June I bought a new Orion/Vixen 80mm f/11. Since then
>I keep getting multiple brightness readings while in
>the Find and Focus mode. It's like I'm on a double
>star only the pixel location does'nt jump when the
>brightness changes as I center the star on the chip.
>The brightness will vary from 3 to 10 units depending
>on the star. To top it off, last weekend it gave me
>three readings and varied back and forth thru all
>three numbers, in order, over and over. It seems to
>guide ok, though I have'nt gotten last weekends pics
>back yet.
>
>Anybody have this happen before? Any suggestions? 
>
>Thanks,
>
>Jeff Allen

Jeff:
Erratic behavior of an St-4 can usually be traced to the formation of ice on 
the chip or chip chamber window. This happens because the dessicant ring in 
the chamber has absorbed all the moisture it can and when the chip cools 
down, moisture in the air in the chamber condenses and freezes. 

The next time this happens, shine a light down into the nosepiece. See if you 
can see crystals on the window or chip. If you do, you need to dry the 
dessicant ring.

To do this, carefully remove the nosepiece and you'll find a ring of what 
appears to be compressed cork (it is not cork). It will probably be loose on 
the face of the ST-4 chamber and surrounding the chip. In older St-4's this 
ring was sometimes glued in place and you will have to be very careful in 
removing it or it will break. (SBIG can provide new rings) Be very careful 
not to disturb or touch the chip or it's mounting wires. Put the ring in your 
oven and bake at 250 degrees for three hours. After cooling, replace the ring 
and reassemble the nosepiece. 

Kent Kirkley 

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