Craig's Pages




Overview
The SAC10 is a very fine camera, but does have one real design issue that can cause problems over time. With use, condensation can form on the back side of the CCD and this water can disrupt the CCD signals. Worse yet, solid particulate matter gets left behind as the condensation evaporates after use. So, now we have things like salts building up between pins that are supposed to be carrying high frequency digital signals. Not good. The end result is usually a severe form of the "bias glow". Some amount of glow is present in every SAC10 as part of the circuit is active during capture (it's a relative of the "amp glow" which is very well controlled on the 10, but it is much less severe). Generally, the camera gets slowly worse as the bias glow builds and the sensitivity drops over time.

Here is a normal level of glow. Note the tight histogram on this 3 minute dark frame

Here is an abnormal level of glow. Note the wide histogram on this 2 minute dark frame


I built most of the SAC10s out there. I was commissioned by SAC to do this, so I know a thing or two about how the camera works. These pictures and this description is meant to help people understand the issue and the normal way of fixing it. If you choose to open your camera and muck about with the innards, it is at your own risk. There are small parts to loose, things can get damaged, and things can be hooked up backwards. In short, you can mess up your camera. IF you choose to go on and do this, any ill effects are yours. If you're not willing to take this risk, don't open the camera.

The Ugly Evidence


Here we have the TEC cooler (white square) of a SAC10 on the CCD carrier board. The CCD is facing down at the moment. The TEC (aka Peltier, aka cooling chip) sits with one side (the hot side aiming up here) on a plate of aluminum (not shown). The other side (the cold side) is against a metal part of a circuit board. That board makes contact with the back of the CCD, cooling it off. The CCD's pins are just next to the TEC to the left and the right of it. The actual data from the CCD to the rest of the camera goes via those black connectors near the edges of the board. But, see the buildup on the left side of the TEC? That should be clean (like the right).


The Fix
Fixing the problem is simple. Get in there, clean the pins off with 90% or better alcohol and a small brush, and seal the pins so that water doesn't get in there. I've tried a few compounds and have been happiest in the long-run with RTV Silicone (aka silicone caulk). The rubberized paint stuff works, but may not hold up as well over the long haul. But, the goal here is to keep water from condensing on these pins. Another option is to cover the pins with a layer of foam to act as an insulator. The goal here is just to keep the pins covered. Either seal them so that water condensation doesn't get in or drop the airspace there to a small enough volume that water won't condense.

Doing this will break the seal in the CCD chamber. To get a really good seal again, you need to replace a neoprene gasket. With some thick neoprene, you can make one yourself. You can try to reuse your old one but you may well dew up more than before. If you do, you can try baking the camera (see below) and that may or may not help.

Getting in

1) Start by removing 3 of the screws from the fan and twisting it a bit to let you get at both the hex screws that hold the back plate in place



2) Next, remove the back plate but don't go too far with it as the TEC wires and a ribbon cable are still attached. Remove one end of the ribbon cable (either). You can leave the TEC power wires (red and black coming off the backplate and heading into the camera) in place if you're lazy like I am. Or you can desolder them here and make your life a bit easier for the next steps.



3) Slide the black tube off either entirely (if you removed the TEC power lines) or like this if you did not. You'll now see either 3 small Philips screws or 3 small Allen screws that hold the "midplate" to the front of the camera. What we see here are the 3 circuit boards of the SAC10. They are held onto the midplate by 4 long screws. Those screws can stay, but the 3 around the perimeter that attach the midplate to the front of the camera get removed. When you do this, you will open up the sealed CCD chamber.




4) Remove the midplate from the front. When you do so, if you turn it over you will see something like this. Your foam will be thinner as this is a new piece of thick foam designed for thin optical windows. Some had smaller pieces of foam and thicker windows. This is neoprene foam and it makes a nice seal on the chamber once compressed. Remove your old foam and window and set aside.



5) Under the foam you will see 6 Nylon screws (white). Remove them and you should be looking like this


6) Feed the TEC wires through the hole a bit and GENTLY remove the CCD carrier board. The wires will keep you from removing it all the way (if they're still soldered on). That's fine. But, there are pins on this board that go through the midplate that you need to be careful with. At this point you should see something like we saw above - crud on the back of this board. Clean it off using high-grade (90% or better) Isopropyl alcohol on a brush and seal the pins up.

Assembly is the reverse, but here are a few things to note:

- When reattaching the CCD carrier board to the midplate, make sure that a) you've got the right orientation and b) that you're not "off" by one set of pins. This is not always easy. Bending a pin is a real possibility so make sure you are lined up before giving any real force.

If you removed the TEC wires and now are wondering which darn way the CCD carrier board plugs in, this should help. Pay attention to the pattern of the small wires and contacts inside the CCD and the location of the vent holes on the midplate. Get it to look like this and it's not in backwards.



Remember - ideally you will replace that gasket to get a good seal. Once compressed you won't get as good a seal again. During the reassembly of the CCD chamber, I find it best to have the CCD aiming up, put the foam on, the glass on, and then the front of the camera on. Get that as close to the right position as possible and then hold the whole thing and flip it over. Press down on the midplate and insert the screws. Once each one is threaded on enough to hold, look at your work. With care and something like a latex glove, you may be able to reposition the optical window a bit. Look very closely for dust in there.

When re-attaching the ribbon cable, have a look at the picture in Step 2. If the red stripe is towards the middle of the 3-board stack, it should be towards the "fan" wires.

Baking the Camera
If the camera is reassembled in moist environment, there is now moisture trapped inside the CCD chamber. If the seal isn't perfect and you've used the camera, odds are there is moisture trapped inside the CCD chamber. There are a few ways to get it out.

1) Put the camera in a sealed box (Tupperware) with some dessicant. Hobby stores / craft stores will sell the stuff. Put them together and let them sit for a week or so.

2) Bake the camera.

As #1 is pretty simple, I'll only cover #2. The goal here is to heat the camera and air up to about 120F and keep it there for several hours to drive moisture away. You may need to get creative and odds are you'll want some kind of digital temperature probe to help keep you from melting your camera. 120F is fine. A bit of time at 130F is fine. Don't start thinking that if 120F is fine, 240F is twice as good. You'll end up with melted camera bits.

I have done this myself in a kitchen oven, in a toaster oven, and in a metal box with a hot air gun shooting into it. The goal is to have warm, dry air around the camera for a few hours. For both oven methods, I could not set the oven to that low a temp, so I had to turn the oven on, monitor the temp and shut it off, keeping things between 110 and 130F. With the gas oven, a byproduct of combustion is water which, of course, makes the oven have hot wet air rather than hot dry air. The idea here is to heat things up in there, open it up to exchange the air and let the hot metal box reheat the new air and your camera. How you go about this is up to you. (An Ez-bake oven is something I considered... get creative).