I have been collecting stock Bally and Stern solenoid boards and checking the spacing between the J3 and J4 headers on the right side. There are three different Stern solenoid boards - Revision A, B, and C.

SDU-10B Stern Solenoid Driver Board Revision A: This board has the large copper traces around the outside of the board. It says Stern SDU-100 and rev 0 or 3, in the middle left end of the board. Most of the rev 3 boards have a blue solder mask. This board has a 1450 mil spacing between the J3 and J4 connectors. My Solenoid Plus Sound board version A will fit this Stern solenoid driver board.



SDU-100 Stern Solenoid Driver Board Revision B: This board has B432 in the lower left corner. It comes in two versions. One, like the one pictured, as a very detailed silk screen which outlines and labels everything on the board. The other, has a minimal silk screen. This solenoiod drivr board has a 1500 mil spacing between the J3 and J4 connectors. My Solenoid Plus Sound board version B will fit this Stern solenoid driver board.



SDU-100 Stern Solenoid Driver Board Revision C: This board has written STERN, a date, and Rev C in the middle of the board under the left corner of the big 5v heatsink, like the one pictured. This board has a 1500 mil spacing between the J3 and J4 connectors. My Solenoid Plus Sound board version B will fit this Stern solenoid driver board.