[osikasculptor]

I would make sure all electrical connections are plugged in. 4th valve servo is channel 8 on my receiver. When radio and machine is turned on and the pump is off see if that dial moves the servo on the block (or rather listen if you hear it move) On mine the pressure valve is screwed all the way in and this dial then adjusts the pressure with the mix toggle on the right in the down position.

Beyond that it could be the servo or a bunch of other things to track down and trouble shoot? Martin "DiggingwithMartin" on you tube does a lot of repair work for guys who own these and is super nice!

Also lots of guys on this forum who have super in depth knowledge about radios and everything else.. and who are also super helpful!