MP 301 Document Feeder will not duplex.

[Macgyver]

When making 2 sided copies the ADF will not duplex, it will feed in the first orriginal, then instead if inverting it, the next orriginal will feed in and the machine will jam and display a #1 jam code. The reason for the jams is that the feed solanoid does not come on and the PU roller stays down and immediatly after feeding the first orriginal in the next starts to feed. If one orriginal is put in the feeder it will work fine but the PU roller will stay down and it rubs on the tray.

Here are some facts, you can't turn on the solanoid in the service mode.
24 volts is measued at the solanoid at idle, mostlikely ground switched.
I have another machine I have been taking parts off of I have replaced the ADF, the ADF harness, BICU, Controller and BICU EProm

[Brianneoe]

You need to replace both the solenoid (sic) and the IO board as a set. This is a known issue with this machine. Does not happen often but don't replace the IO without the solenoid or you will blow another IO

[Mark Bbb]

On some ADF models there is a junction gate guide flipping to another (duplex) position.
Sometimes these junction gate guides gets stuck (e.g. on the adhesive sound seal).
Have you checked that?