"RE: Baking the 416XT - (longish)" in the Meade Astronomy Archive

Subject: RE: Baking the 416XT - (longish)
From: Geoff
Reply To: mapug@shore.net
Date: Sat Apr 09 06:06:25 2005

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MDS,

=20

My 416XTE is just back in service today after experiencing icing - right =
now
it is doing an LRGB of M95. I pulled it apart this afternoon and baked =
the
dessicant. It is the third time I have done it - last time was about 20
months ago. Some additional points from my experience:

=20

1. I get reasonable results from baking 3 hours at 120C. I have tried
higher temps but it discolours the dessicant bags (the Meade ones =
anyway),
and I was concerned they might fail inside the camera.
2. It sounds silly but keep track of the various fixings when you take
the front cover off and remove the PCB. You will have the 8 allen head
countersunk screws (from the cover), two plastic washers and two little =
nuts
(from the PCB) to not lose. There are also two plastic spacers on the =
studs
under the PCB but these can stay put unless you upend the open camera =
body.
3. Note the orientation of the shutter cabling connector when you
unplug it to get the shutter assembly out of the way. The plug does not =
seem
to be polarised but the ribbon cable is colour coded, so keep track of =
which
side is which. You can also remove the O-ring at this time.
4. Be careful lifting the PCB off the peltier. The chip is bonded to
the peltier (or seems to be) and needs some force to let it loose (or at
least mine did the first time). I use a screwdriver under the edge of =
the
slot in the PCB, supported off the camera body with a pencil or similar =
so
as not to damage the rebate for the O-ring. After some gentle persuasion =
on
the side away from the peltier wires you can feel the PCB let go and =
then it
is not too difficult to get it up.
5. Be careful of the temp sensor wires from the PCB to the camera inner
case. They are fragile and could break when the PCB is lifted out of the =
way
to expose the dessicant bags. Of course you could carefully detach the =
temp
sensor to remove the PCB altogether, but then you would have to fix it =
back
somehow with some thermally conductive adhesive. I have not done this.
6. With the PCB hanging off to one side the dessicant bags can removed
and put into the oven to bake. Note how they are arranged in the camera =
body
before you take them out. If they don't go back properly they will not =
let
the PCB sit down and the chip will not mate properly with the peltier. =
Today
I did not have access to the kitchen oven because my daughter was baking =
my
mother a birthday cake, so I used the little sandwich griller in my =
workshop
and it went OK (the t'stat is not as good as the big oven, but it was a =
very
nice cake)
7. Make sure that for the three hours or so the bags are cooking, the
camera, O-ring and shutter assembly are safe and don't get dusty. I put =
them
in a plastic bag until reassembly time.
8. Before reassembly I give the camera body a vacuum out. I also vacuum
both sides of the PCB and around the shutter assembly, and around the =
O-ring
rebate. You don't want to suck the chips off the PCB so use something =
gentle
- I use an old household vacuum cleaner with a neoprene tube about 8mm =
dia
attached to the nozzle. It gets into the tight areas and gets the dust =
out
without too much force.
9. The replacement procedure is the reverse of the dissassembly. I use
a little thermally conductive heat sink paste between the chip and the
peltier - just a smear. Check the PCB is not catching on the mounting =
studs
or the inside of the body, and that the chip is seated on the peltier. =
There
is a little deflection to the PCB when the nuts are tightened - =
presumably
to keep the chip seated. There might be a trick to the O-ring - mine =
seems
too small and wants to cut corners on the inside of the camera. So I =
stretch
it just before it goes back together and then seat it in the rebate and =
put
the cover on before it shrinks back to original size. It is the most =
tricky
part of the whole exercise. Then with the cover on and nipped down but =
not
tightened check right around the gap between the cover and body to make =
sure
the O-ring is in place and has not snuck inside the body or gotten =
pinched.
If OK tighten the screws.
10. It takes a while for the dessicant to take the moisture out of the
air inside the camera. Tonight I was in a hurry, put the camera back on =
the
scope, fired it up and started imaging. Tragedy - water on the chip. But =
it
went away after an hour or so with the chip temp set to +0.5C. Then I
reduced the temp to -10C for imaging.
11. The data set is very small but there seems to be a correlation
between the temps the camera is set to and the longevity of the =
dessicant -
if the camera operates at too low temps it seems to ice up quicker.

If you want email me privately and I can send you photo's of the =
trickier
parts of the operation. There are also a number of web resources - Chris
Heapy has some pics on his site.

=20

Geoff Todd

Lugarno NSW

Australia

=20

-----Original Message-----
Behalf
Sent: Saturday, April 09, 2005 5:28 AM
Subject: Re: Baking the 416XT -=20

=20

Thank you all for replying to my question regarding baking the dessicant =
frm
the 416xt. It would seem to me that Tom Galland gave a very good,
step-by-step, procedure. Assuming one goes through with it, due to some
conflicting replies, I'm still unsure as to what temperature and how =
long
the dessicant has be oven baked.=20

And, has anyone actually done this?=20

Thanks again to all.

MDS

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<div class=3DSection1>

MDS,

 

My 416XTE is just back in service today after =
experiencing
icing – right now it is doing an LRGB of M95. I pulled it apart =
this
afternoon and baked the dessicant. It is the third time I have done it =
–
last time was about 20 months ago. Some additional points from my =
experience:

 

<ol start=3D1 type=3D1>
<li class=3DMsoNormal>I get reasonable results from baking 3 hours at =
120C. I
have tried higher temps but it discolours the dessicant bags (the =
Meade
ones anyway), and I was concerned they might fail inside the =
camera.</li>
<li class=3DMsoNormal>It sounds silly but keep track of the various =
fixings
when you take the front cover off and remove the PCB. You will have =
the 8 allen
head countersunk screws (from the cover), two plastic washers and =
two
little nuts (from the PCB) to not lose. There are also two plastic =
spacers
on the studs under the PCB but these can stay put unless you upend =
the
open camera body.</li>
<li class=3DMsoNormal>Note the orientation of the shutter cabling =
connector
when you unplug it to get the shutter assembly out of the way. The =
plug
does not seem to be polarised but the ribbon cable is colour coded, =
so keep
track of which side is which. You can also remove the O-ring at =
this time.</li>
<li class=3DMsoNormal>Be careful lifting the PCB off the peltier. The =
chip is
bonded to the peltier (or seems to be) and needs some force to let =
it
loose (or at least mine did the first time). I use a screwdriver =
under the
edge of the slot in the PCB, supported off the camera body with a =
pencil
or similar so as not to damage the rebate for the O-ring. After =
some
gentle persuasion on the side away from the peltier wires you can =
feel the
PCB let go and then it is not too difficult to get it =
up.</li>
<li class=3DMsoNormal>Be careful of the temp sensor wires from the PCB =
to the
camera inner case. They are fragile and could break when the PCB is =
lifted
out of the way to expose the dessicant bags. Of course you could =
carefully
detach the temp sensor to remove the PCB altogether, but then you =
would
have to fix it back somehow with some thermally conductive =
adhesive. I
have not done this.</li>
<li class=3DMsoNormal>With the PCB hanging off to one side the =
dessicant bags
can removed and put into the oven to bake. Note how they are =
arranged in
the camera body before you take them out. If they don’t go =
back
properly they will not let the PCB sit down and the chip will not =
mate properly
with the peltier. Today I did not have access to the kitchen oven =
because
my daughter was baking my mother a birthday cake, so I used the =
little
sandwich griller in my workshop and it went OK (the t’stat is =
not as
good as the big oven, but it was a very nice =
cake)</li>
<li class=3DMsoNormal>Make sure that for the three hours or so the =
bags are
cooking, the camera, O-ring and shutter assembly are safe and =
don’t
get dusty. I put them in a plastic bag until reassembly =
time.</li>
<li class=3DMsoNormal>Before reassembly I give the camera body a =
vacuum out.
I also vacuum both sides of the PCB and around the shutter =
assembly, and around
the O-ring rebate. You don’t want to suck the chips off the =
PCB so
use something gentle – I use an old household vacuum cleaner =
with a
neoprene tube about 8mm dia attached to the nozzle. It gets into =
the tight
areas and gets the dust out without too much  =
force.</li>
<li class=3DMsoNormal>The replacement procedure is the reverse of the
dissassembly. I use a little thermally conductive heat sink paste =
between
the chip and the peltier – just a smear. Check the PCB is not
catching on the mounting studs or the inside of the body, and that =
the
chip is seated on the peltier. There is a little deflection to the =
PCB
when the nuts are tightened – presumably to keep the chip =
seated. There
might be a trick to the O-ring – mine seems too small and =
wants to
cut corners on the inside of the camera. So I stretch it just =
before it
goes back together and then seat it in the rebate and put the cover =
on
before it shrinks back to original size. It is the most tricky part =
of the
whole exercise. Then with the cover on and nipped down but not =
tightened
check right around the gap between the cover and body to make sure =
the
O-ring is in place and has not snuck inside the body or gotten =
pinched. If
OK tighten the screws.</li>
<li class=3DMsoNormal>It takes a while for the dessicant to take the =
moisture
out of the air inside the camera. Tonight I was in a hurry, put the =
camera
back on the scope, fired it up and started imaging. Tragedy – =
water on
the chip. But it went away after an hour or so with the chip temp =
set to +0.5C.
Then I reduced the temp to -10C for imaging.</li>
<li class=3DMsoNormal>The data set is very small but there seems to be =
a
correlation between the temps the camera is set to and the =
longevity of
the dessicant – if the camera operates at too low temps it =
seems to
ice up quicker.</li>
</ol>

If you want email me =
privately and I
can send you photo’s of the trickier parts of the operation. There =
are
also a number of web resources – Chris Heapy has some pics on his =
site.

 

Geoff =
Todd

Lugarno =
NSW

Australia



 

-----Original =
Message----- 
From: =
style=3D'font-weight:bold'>On Behalf
Sent: Saturday, April
09, 2005 5:28 =
AM 
To: =
Subject: Re: Baking the =
416XT - 

 

<div>

Thank
you all for replying to my question regarding baking the dessicant frm =
the
416xt. It would seem to me that Tom Galland gave a very good, =
step-by-step,
procedure. Assuming one goes through with it, due to some conflicting =
replies,
I'm still unsure as to what temperature and how long the dessicant has =
be oven
baked. 

</div>

<div>

And,
has anyone actually done this? 

</div>

<div>

Thanks
again to all.

</div>

<div>

MDS</font=
>

</div>

</div>

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