IBM 3270 Manual page 240

Instructions for Setting 3274 Model .51C Transmit Level
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Switches (U.S. and Canada Only)
(
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u
1.
Open the customer access area door on the bottom left of the Model
51C. To unlatch the door, turn the slotted screw head counterclockwise
with a coin.
Slotted Screw Head
(Turn counterclockwise to open)
2. Set the Transmit Level switches on or off as indicated in the boxes
below. Push the switch up for on and down for off.
Transmit Level
-1 dB -2dB
DD
-4dB -8dB
DD
Line
Pri foigpeed
Secl.QJ
This panel is I ocated in the customer access area.
Appendix H. Planning for 32.74 Model 51C Switch Settings
H.-3