MPU (A1-J5)	Driver (A3-J1)	Function
1	11	Solenoid 7
2	12	Solenoid 8
3	4	Lamp Data 4 (LD4)
4	2	Lamp Data 3 (LD3)
5	1	Lamp Data 2 (LD2)
6	3	Lamp Data 1 (LD1)
7	19	100's Chime Solenoid
8	18	1000's Chime Solenoid
9	9	Solenoid 6
10	20	10's Chime Solenoid
11	21	Knocker Solenoid
12	8	Outhole Solenoid
13	17	Strobe 9 (DS9)
14	15	Strobe 8 (DS8)
15	16	Strobe 7 (DS7)
16	14	Strobe 6 (DS6)
17	13	Strobe 5 (DS5)
18	10	Strobe 4 (DS4)
19	7	Strobe 3 (DS3)
20	6	Strobe 2 (DS2)
21	5	Strobe 1 (DS1)
22	24	Both are not used
23	23	+5 VDC
24	22	Ground

Notice pin 22 is not used on A1-J5 and pin 24 is not used on A3-J1

All System-1 machines have a set of solenoids which are the same. These include the outhole, the 3 chime boxes, and the knocker. Three additional solenoids, which may vary from machine to machine, are labeled as 6, 7, and 8. Besides the flippers, there will never be more than 8 separately driven solenoids on a System-1 machine. Any additional solenoids, like the Kings Drop Target reset on Joker Poker, is driven by a lamp driver, with the help of a secondary driver transistor located on the underside of the playfield.

The lamps are controlled by the nine "DS" and four "LD" signals. The LD signals are four on/off signals for one of the quad flip-flops on the driver board . Each flip-flop can control up to 4 lamps. There are 9 of these flip-flops (SN74175) on the driver. The nine DS signals are used to clock the desired flip-flop (only one flip-flop is clocked at a time). So here's how it works: The CPU turns on or off the desired LD signals. Then one of the nine DS lines is strobed in order to clock the desired flip-flop. When a flip-flop is clocked, it will read it's 4 inputs (LD1 - LD4) and set the corresponding outputs, there by turning on or off up to 4 different lamps.

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