From: Kevin Cooper <kjcooper@t...>
Date: Sat Oct 19, 2002
12:58 am
Subject: ST-7 fan vibration.
Just recently I noticed that
I was getting slightly elongated star
images. Stopping the fan confirmed it as the cause. I ordered and fitted
a SUNON magnetically levitated fan. When I next used the camera, I found
I had a red light leak. On investigation, I found the cause to be the
new fan. Placing an oscilloscope across the power to the fan, I found
large noise pulses on the 12 volts DC. I reduced the pulse amplitude to
an insignificant level by fitting a 10 micro farad tantalum capacitor
across the power leads. It seems that the noise was causing the shutter
sensor led to stay on during the exposure. This not only cured the light
leak and vibration problem, it gave me a greater temperature reduction
below ambient. The fan moves more air than the original.
The fan is a Sunon KDE1204PFVX and cost $10.95 USD.
Kevin Cooper
From: "tedinoue"
<etinoue@c...>
Date: Sat Oct 19, 2002 7:39
am
Subject: Re: ST-7 fan vibration.
Kevin, that sounds good!
Thanks for the lead.
Where'd you get yours?
Also, why the tantalum cap rather than one of the other varieties of
caps? High frequency response?
-Ted
From: "C. Faranda"
<ccd@c...>
Date: Sat Oct 19, 2002 8:35
pm
Subject: Re: [SBIG] ST-7 fan vibration.
Kevin,
Where did you get the fan? I'm noticing some resonance from my fan too.
Regards,
Chuck Faranda
http://ccdastro.net
From: Kevin Cooper <kjcooper@t...>
Date: Sat Oct 19, 2002 9:04
pm
Subject: Re: [SBIG] Re: ST-7 fan vibration.
Hi Ted,
I mail ordered the fan from this site.
www.cyberguys.com
Their part number is 148 0355. I used a
tantalum capacitor because they
are very small. I fitted it across the point where I joined the the new
fan to the wires from the connector. It is just floating on the fan
lead. One point to note is that the leads of the fan are in a different
position to the original and require a new cut out in the back cover to
accommodate them. I used a small round file to make the cut out.
-Kevin
From: "Dave Cole" <dave@n...>
Date: Sun Oct 20, 2002
10:49 am
Subject: Re: [SBIG] Re: ST-7 fan vibration.
Hi,
Is this a straight replacement? No mods, just
pull the old fan, put in the new
fan?
Thanks,
Dave
Nexstar11GPS Tips and tricks
http://www.nexstar11.com
From: Kevin Cooper <kjcooper@t...>
Date: Sun Oct 20, 2002 9:02
pm
Subject: Re: [SBIG] Re: ST-7 fan vibration.
Hi Dave,
Because the Sunon fan has it's leads in a different position, you will
need to make a slot for them like for the original but in different
position. You also need to cut the leads from the fan connector and
solder the new fan leads to the wires from the plug. The tantalum
capacitor is a very small bead with 2 leads. It is polarity sensitive,
the plus lead marked with either a "+" sign or has a bar symbol
near it.
Before soldering the wires and the capacitor together, I split the twin
wires from the plug a small distance and placed shrink tubing onto them
so that when the wires and capacitor leads were soldered together, the
tubing was slipped over the joints and the capacitor leads and shrunk
with a hot air gun. All this done, of course, with the
fan plug, which
also has the led indicator light on it, removed from the circuit board.
If you are not handy with fine electronic soldering or don't have the
gear, I recommend that you get someone who has to do the job. Also, if
your camera is still under warranty, I would not do the modification
without checking with SBIG.
Regards,
Kevin Cooper
From: "Matt Longmire" <matt@s...>
Date: Sun Oct 20, 2002 7:58
pm
Subject: Re: ST-7 fan vibration Strange Result
I believe the issue about
the capacitor lowering the spikes but i
STRONGLY question the correlation between the new fan and the red
light leak.
I can not imaging a single path that adding noise at the fan would
cause the shutter sensor to stay on. I could see readout noise but
not glow from the shutter sensor.
Did you also have a CFW-8 on the system at the time? Perhaps it
could pick up noise and leave its sensor on as it is looking for
communications from the microcontroller in the camera.
Are you 100% sure it wasn't a light leak?
Just skeptical.
Matt Longmire
SBIG
From: Kevin Cooper <kjcooper@t...>
Date: Sun Oct 20, 2002 9:35
pm
Subject: Re: [SBIG] Re: ST-7 fan vibration Strange Result
I am 100% sure the fan
was causing the problem. I proved that it wasn't
the CFW-8 by unplugging it. I also proved it by leaving the fan turned
on but unplugged from the board. I also removed the CFW-8 from the
camera and still had the leak, but the pattern that showed up with the
red filter in was not there. Would you like me to send you private mail
with images with the fan on and the leak gone?
I don't know if I got a defective fan or they
normally generates what
amounted to pulses rather than spikes that were several volts in amplitude.
The only thing I can suggest is that you get one of the fans and try it
yourselves. I got it by mail order from "www.cyberguys.com".
Their part
number is 148 0355.
Regards,
Kevin Cooper
From: "Brian Coote"
<bcoote37@a...>
Date: Tue Oct 22, 2002 6:08
am
Subject: Re: [SBIG] Re: ST-7 fan vibration.
Hi Kevin,
I infer from this that the electrical interference actual originated in the
mag-lev Sunon fan itself ?
Is this correct ?
Brian
From: Kevin Cooper <kjcooper@t...>
Date: Tue Oct 22, 2002 6:34
pm
Subject: Re: [SBIG] Re: ST-7 fan vibration.
Hi Brian,
Yes, the fan was generating noise pulses. I ran it off the camera with a
bench power supply and looked across the leads with an oscilloscope. The
fan was producing large positive pulses. I did not note the exact
amplitude but it was several volts. With a 10 mf capacitor across the
leads, the pulse level dropped to about 200 millivolts,
0.2 volts.
Kevin