Re: [APML] st-4 acting up

[Philip Perkins <pgp@astrocruise.com>]

Hi Bobby,

In the past I've had odd bouts of misbehaviour such as you describe.  They 
were all related to power - of course you already know about the 
sensitivity of the ST-4 to under-voltage, but it's worth mentioning a few 
things to check:

- check the voltage both at the PSU connector *and* inside the ST-4, with 
the ST-4 powered up. There can often be an ohmic joint somewhere in the 
connectors, and at 12v it only takes a small amount of resistance to drop 
the voltage.

- even if the voltage looks OK it's worth removing *all* external 
connectors (including ST-4 head) and cleaning the contacts. Use a 
proprietary contact cleaner, or dry cleaning fluid (first making sure it 
does not dissolve plastic parts in the vicinity).  Ohmic joints will build 
up anywhere over time, especially in damp conditions.

- if your ST-4 still has the original bridge rectifier be suspicious!  It 
is *very* prone to failure.  It usually cuts out intermittently but can 
also cause low voltage.  The replacement part has a heat sink fitted.

- it's worth having a general probe around inside the box, looking for 
accumulated dirt, spiders webs, etc that can cause earth leakage in 
critical parts of the circuit.  Also while it is powered up, tap various 
parts of the circuit board and components with something insulated, to see 
if it has any effect.  It's possible for there to be a loose connector or 
dry solder joint.

- it doesn't sound like a chip frosting problem, but I expect you've 
checked that anyway..

--Philip
-------

At 22:03 14/07/2004 -0500, you wrote:
>It looks like my st-4 is needing several dark frames to settle down where it
>can make true readings. This is after a 30 min+ start-up. It's warm here in
>TX (90 deg at sundown) if that has anything to do with it. It's never been a
>problem before during the heat.
>Anybody seen this behavior and can you tell me what's going on?
>I had this problem the other night and finally got it settled down where it
>worked OK all night. I took 3-4 dark frames tonight beforte it settled down
>to good readings.
>Bobby Middleton
>
>
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Philip Perkins
<pgp@astrocruise.com>
Wiltshire UK & Luberon France
www.astrocruise.com

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