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Thanks Dunk. In my setup the fan runs directly off the 12V supply produced by the controller power pack, and thus it is constant. The problem does not occur when the controller is not sending power to the TEC. As soon as the controller relay closes and sends power to the PWM the interference starts, and once the setpoint temperature is reached and the controller drops the PWM relay to shutdown the TEC, the interference stops. So I don't think it is the fan causing it. The problem seems to be TEC power related or lack of proper earthing of the cold finger (which I am leaning towards in the absence of anything else). I am thinking of running an earth wire from the controller negative to the cold finger to test, but if the cold finger is isolated from the camera earth/frame I am not sure It's will improve the situation. I need to check the camera frame to cold finger continuity. If, in putting the cold finger on the carbon fibre spacer, I have isolated it from the camera electrically perhaps it is acting as an antenna and inducting a signal into sensor image - if that's even possible.
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