You likely already know, but for other readers benefit, the round PCB's are supplied by DRS with their imaging core and are the support electronics for the core. The Sterling Cooler will be controlled by these PCB's. The Linear cooler design uses field coil inductive drive of the magnetic piston so expect to see AC on the drive wires. The frequency of the drive is dictated by the mechanical characteristics of the linear cooler as the piston oscillates in a resonance mode working against a precision spring. These coolers are quite noisy when cooling down to operating temperature (77K) but should then drop into teh 'mainatin' mode that just needs to cope with any sensor self heating, thermal losses in the Dewar and incoming energy through the window. This 'maintain' mode has the cooler running at idle with lower cooler noise. A cooler should reach operating temperature in less than 15 minutes but I prefer to see it reach that maintain state in 10 minutes or less. The longer it takes teh cooler to reach operating temperature, the poorer the condition of the cooler. This can be due to internal wear or some loss of the Helium gas fill, reducing cooling performance. 'Dead' coolers will never reach operating temperature as they have worn ot seals, failed internal parts or loss of too much Helium gas fill. They become a paperweight.
Fraser