Use the 4600 manual at mikesarcade.com as your monitor is part of the 4600 series. The last page of the 4600 manual shows the locations of the plug-in boards and adjustments.
There are actually three plug-in circuit boards on the 4600 series. From the rear view, all the way to the far left of the main board is the power regulator plug-in board. Towards the right of the board are TWO plug-in boards: the farthest right is the "hor/ver" deflection board (also called the "X/Y" board). Now to the left of that board is the "Interface Board" which is where your color video and sync signals from the gameboard go to. The Interface board usually has a paper label on the parts side with a number like P305, P317, P318, etc on it.
These boards do show up on ebay alot.