IBM 1627 Manual page 15

Forward Resistance Reverse Resistance
Reverse Resistance should measure at least 10 times forward resistance
Figure 2-2. Transistor Testing
Fuses, An effective way to locate a blown fuse is to
connect a voltmeter across it. If the fuse is blown,
the terminal voltage of the power supply will indi-
cate on the meter. If there is no meter indication,
and the power supply is operating properly, the fuse
is good. Be sure to use the proper scale on the
meter.
SERVICING PROCEDURES
1627 Disassembly
The 1627 plotter is easily disassembled for main-
tenance or repair. Normal disassembly is limited
to removal of the cover, plotter circuit board, and
plug-in power supply. No special instructions are
required for removal of individual components on
the main assembly, the circuit board, or the power
supply.
Cover
To remove the cover, remove six binder head screws
from the bottom of the cover (Figure 2-3).
WARNING: Remove only those screws designated A
in Figure 2-5. Removal of screws other than those
designated A, B or C will cause mechanical mis-
alignment or damage.
Circuit Board
After removing the cover, remove the connector
bracket by removing screws marked C in Figure 2-3.
2.4
Remove six round head screws that fasten the circuit
board to mounting standoffs on the main chassis and
the power supply chassis. Carefully disengage the
assembly from connectors J1 and J2 on the power
supply chassis.
WARNING: The circuit board is flexible. Twisting
the board during removal and replacement can crack
the etched pattern.
Power Supply Chassis
Remove the cover and the screws marked B in
Figure 2-3, Remove the circuit board then remove
the two hexagon head screws that fasten the extended
tabs on the power supply chassis to the side frames.
The power supply chassis can now be removed by
pulling it straight back.
WARNING: Remove only those screws designated
A, B, or C in Figure 2-3.
Removals and Replacements, and Adjustments
With the exception of replacement and adjustment of
the drum step motor, the carriage step motor and
the carriage drive cables described in the following
paragraphs, no special instructions are required for
adjustments or replacement of components in the
1627.
Step Motor Replacement and Adjustment
Location of the carriage and drum step motors, M3
and M4 respectively, is shown in Figure 2-4 and
2-5. The step motor and its primary gear train are
matched at the factory and must be replaced as a
complete assembly. To replace either of the step
motors, proceed as follows:
1. Disconnect power from the plotter. Remove
the cover, circuit board, and power supply
in accordance with the 1627 disassembly
procedure.
2. Clip lacing twine from the step motor leads
to separate them from the wiring harness.
Remove the orange, red, and brown wires
from the three limiting resistors mounted
on the side of the main assembly. Note
these connections carefully so that the
replacement motor can be connected
properly. Disconnect the remaining black
wire from the standoff insulator.
3. Remove the two Allen head cap screws
which mount the motor to the main
assembly. Remove the motor and primary
gear train.