The CDU in the pics above is a 72 variant - all good there. The MSU is a LTN-92 variant - has the amber align light rather than the green ready nav light which can be found on the LTN-72 MSUs. No issues here as it is just an on/off switch for the INU. Also remember that behind the middle panel on the MSU is the hidden test/bias switch. With power on this switch can be turned to bias and from there the current bias and scale factor figure can be read direct from the INUs core memory. These will be updated figures that are more accurate than the figures that can be found on the INUs front bias label. Erik as we have discussed in PMs the INU requires two power sources to turn on. A primary 115vac 400hz and a +28VDC (battery backup) source. It requires this 28v just to initiate turn on. This power can be removed after turn on and the INU will continue to operate. When a source of 115vac 400hz is fed into the INU a high pitched frequency whine will be heard (from the power supply) prior to turn on. This just tells me that there is power going to the INU.
The INU has some BITE (built in test) indicators. 3 can be found on the power supply externally and another 5 bite indicators can be found on the monitor board behind the panel beneath the power supply. Take this smaller cover off and the bottom cct bd will have 5 round disks - hopefully they will be black. If any are yellow this indicates that the unit has seen some fault during its life. These bite indicators can be easily reset with a magnet as they are magnetically latched.
From memory bite indicators are: Power supply PSM1 - Power converter issues. PSM2 - +5VDC fail. PSM3 - +13VDC fail
Monitor board DS1 - Gyro spin issues - from memory
DS2 - servo no-go (round servo board problem on the gimbal assy)
DS3 - Overtemp
DS4 -
DS5 - Quantizer board problems (large board in the front gimbal area
DS6 - Bias wipe Computer board issue