Image shift X and Y have failed at maximum

[peter-spencer]

The SEM's electron beam can be steered around the sample over a limited range using the IMAGE SHIFT X and Y controls but this appears to be jammed fully at maximum for both axes.

As a consequence, the SEM is unusable at anything other than low magnifications because the central image area is deflected fully to one corner of the CRT readout.

[peter-spencer]

I have identified that the front panel controls are working but the reference voltages are not correct and therefore adjusting the potentiometers makes no difference to the signal sent to the driver board N80NA01. This is consistent with a power supply issue or a problem with one or more of the Zener diodes on the N80NA01 board.

[peter-spencer]

I have removed the Op-amp, output transistors and output resistors on N80NA01 to disable the Image Shift function.