CCD-world: RESET PROBLEM

[MYPIXEL at aol.com]

The following was posted to CCD-world:

******************jj
Roger,

This theory sounds much more reasonable. When a car stops working.. .  it is 
usually not the engine.

Can you let us know what the culprit is (was) ..  ?

Jim
*******************jj

In a message dated 4/26/00 6:57:50 AM Pacific Daylight Time, 
roger at ctios1.ctio.noao.edu writes:

<< Subj:     CCD-world: RE: RG threshold shift ?
 Date:  4/26/00 6:57:50 AM Pacific Daylight Time
 From:  roger at ctios1.ctio.noao.edu (Roger Smith CTIO - rsmith at noao.edu)
 Sender:    owner-CCD-world at astro.ku.dk
 Reply-to:  CCD-world at astro.ku.dk, CCD-world at astro.ku.dk
 To:    ccd-world at astro.ku.dk
 
 The following was posted to CCD-world:
 
 Dear CCD-World,
 
 Thanks everyone for your feedback.  Given that "most experience is bad
 experience", its good to learn from the experience of others!
 
 One thing that I failed to mention was that the CCD was not only in its
 dewar and cold when the fault appeared but that our CCD controllers and
 dewars are not normally separated: the dewar and controller remained
 mated from the time the system was working in the lab to the time the
 fault was observed at the observatory.  So I don't believe static
 discharge is a likely explanation.  The supplies have clamps on their
 outputs to protect against over-voltage.
 
 Paul Jorden's suggestion (attached) that there is an open circuit in RG
 is interesting one, and it underlines the importance of not leaping to
 conclusions that the CCD (or its manufacturer) are to blame.
 
 Given that the RG capacitance
 is very low, it is plausible that I am
 driving RG through a stray capacitance that bridges an open circuit in
 the wiring or connector.  The linear layout of the cabling doesn't
 appear to be capable of producing this much stray capacitance to me but
 I can't rule out the possibility.  I can setup a cold loopback test on
 the wiring to the mount.  But how can I test whether coupling to Reset
 Gate is capacitive within the CCD assembly?  ...Maybe careful
 capacitance comparison with the other amp will work.
 
 Another possibility is a high resistance contact producing much longer
 settling time on RG.  200 Kohm would be enough for RG at the CCD to
 only slew half way.  This should show up as a triangular reset
 feedthrough pulse.  A definitive test would be to extend the RG pulse
 length.
 
 I'll let you know what I find when I have the system back together
 again.
 
 Roger
  >>
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