IBM 5251 11 Maintenance Information Manual page 28

111
(continued)
Check the control line at the planar (brightness or
contrast) for a change in voltage as the control is
turned fully counterclockwise and then clockwise.
The voltage limits are:
Fully Fully
CCW CW
Brightness
o
Vdc 8.5 Vdc
Less than
Contrast 3.0 Vdc 8.5 Vdc
Are the voltage limits correct?
Y N
111
Check the center tab of the control.
Turn the control fully counterclockwise and then
clockwise.
Are the voltage limits present at the center tab of the
failing control?
Y N
Check for 8.5 volts on one top tab of the failing
control.
Check the lower tab of the failing control.
The voltage should be:
o
volts if checking the brightness control. Less than
3 volts if checking the contrast control.
Are the voltages correct?
Y N
The cable or the planar is failing.
- Trace the failing line back to the planar.
Replace the control.
Check the control line for an open.
Inspect the interposer.
Replace the planar (set the jumpers correctly on the
new planar (103) (105) ).
Suggested action for an intermittent problem:
• Analyze the suspected line; inspect all the connector
contacts.
• Replacement sequence:
Control
Planar
- Control Panel Cable
Maintenance Procedures 5251 MIM 1-9