IBM 5150 Hardware Maintenance Manual page 153

Error
Description
Diagnostic Action
No Printing
6. Position Printer Power switch to ON. Move
print head to the left-most position. Check
for a Down level (approximately 0 Vdc) to
an Up level (approximately +5 Vdc) meter
deflection at CN6-20 on the Driver Circuit
card (see Section 5, "Locations") while
moving the print head to the center of the
print line. Use the ground pin on the Driver
Circuit card for common.
Is there a Down level to an Up level
deflection?
YES:
Go to step 7.
NO: Is there a constant Down level?
YES:
Go to page 1400-6, "Power
Supply Check." Replace the
Left Margin Sensor if the
power supply checks good.
(See Section 3, "Removal/
Replacement. ")
NO: Position Printer Power switch
to OFF. Check continuity from
CN6-20 (Driver Circuit card) to
Left Margin Sensor terminal 1
and from CN 6-15 to Left
Margin Sensor terminal 2. (See
Section 5, "Locations.")
Either line open?
YES: Replace Print Mechanism
assembly (see Section 3,
"Removal/
Replacement").
NO: Replace Left Margin
Sensor (See Section 3,
"Removal/
Replacement").
1400-12