I've had an ST-7 for a number of years now and I've avoided using it because of frosting issues. No matter how many times I charged the desiccant plug as soon as I started to go below 0 deg the chip would frost up (funnily enough not the guide chip) and it would take a long time to sublimate off. Consequently I hardly ever used it for the purpose it was bought for, variable star measurements.
I had thought of trying to dehumidify the chamber before putting the plug in but I couldn't think of a simple way to do it. Well I had a bright idea the other day (well for me that is), what if I were to put the camera in a plastic bag with zip lock, along with a closet camel and seal the bag over night. I could then charge the plug in the oven, wrap it in plastic to keep it dry over night and the next day crack the plastic bag and slip my hand inside and screw in the plug.
The plastic bag I used was one of those vacuum storage bags. I didn't vacuum it because i figured that if i did, when I cracked the bag humid air would enter and defeat the purpose. So I just squeezed most of the air out to reduce the volume, sealed and left it over night with camera and camel inside.
After putting the plug in I switched on the camera and turned up full cooling to quickly reach -8 deg. Not a sign of frosting. I am one happy chappy
I'm still to check it after a day or so but if you are having the same issue this solution seems to work a treat.
