IBM AT 5170 Technical Reference page 88

The speaker connector, J19, is a 4-pin, keyed, Berg strip. The
pins are numbered 1 through 4 from the front of the system. The
pin assignments are as follows:
Pin Function
1
Data out
2
Key
3
Ground
4 +5 Vdc
Speaker Connector (J19)
The power LED and key lock connector, J20, is a 5-pin Berg
strip. The pins are numbered 1 through 5 from the front of the
system. The pin assignments are as follows:
Pin Assignments
1
LED Power
2
Key
3
Ground
4 Keyboard Inhibit
5
Ground
Power LED and Key Lock Connector (J20)
The battery connector, J21, is a 4-pin, keyed, Berg strip. The
pins are numbered
1
through 4 from the right of the system. The
pin assignments are as follows:
Pin Assignments
1
Ground
2
Not Used
3
Key
4
6
Vdc
Battery Connector (J21)
1-72
System
Board