Do you have the symptom only using AEC? If the end user isn't sure, shut the AEC off at the beginning of troubleshooting and work from there. Otherwise, you may go through a lot of grief only to learn the problem is related to AEC.
Intermittent or constant rotor/prep and no green ready light: Check prep switch (not as likely) Check I/O (high probability)
1. Check the 5.0 volt supply on the motherboard in the generator. If that voltage is not stable, you can lose prep. In severe cases it will blow fuse F4 on the power supply board and then, of course, you won't get prep at all. There were a few issues in that area. Check the zeners and capacitors related to the 5.0 volt supply on the motherboard. This is a rare problem.
2. A defective prep/rotor switch. When they start to fail (and this can happen with prep or expose switches) they become known as a bouncing switch and do not give a solid signal which raises havoc with digital when it's looking for either an on or off state. Check switch for good continuity with the generator off.
3. Check the 30 mfd rotor capacitor. Rare, but it can happen.
4. Check for any loose rotor wire connections. Check the tube stator windings and ohms. Go to our X-Ray tube tab and click underlined red link for ohms.
5. The I/O board, about the last reasonable cause. The I/O board has had it's issues over the years. The mA rotor board is another possibility, but is less likely. The failure rate of the I/O board for this symptom is about 90%
That being said if you order a replacement I/O board from us and you have the same problem then chances are the problem is NOT the I/O board. Our boards are tested before they are shipped. Go back again and check the rotor circuit, prep switch and if those things are ok, suspect the mA/rotor board. It can give the same symptom as intermittent no ready or constant no ready.