Mallinckrodt Nellcor N-20PA Service Manual page 33

4.7.5 Replacing Fuses
4.7.6 Replacing the DB-9 Connector
4.7.7 Adjusting Printer Darkness
6. Reset the clock (see paragraph 4.7.3, Setting Date and Time).
Two fuses (F1 and F2) are located on the auxiliary PCB. Fuse F1 may open to
protect the CPU and its associated components from damage if the power supply
malfunctions. Fuse F2 may open to protect the printer from damage due to
excessive voltage if the printer head jams or if it has been physically damaged.
Refer to the auxiliary PCB schematic for the locations of F1 and F2.
To replace the DB-9 connector:
1. Disassemble the N-20PA (see Section 5); the connector is on the main PCB.
3. Using a low-power soldering iron, unsolder the connector from the PCB and
remove it.
Note: Save all Teflon tubing, ferrite blocks, and insulating materials for the
replacement connector.
3. Install ferrite blocks between the plastic lead spacer on the connector and the
PCB.
4. Insulate connector pin numbers 2, 3, and 5 with Teflon tubing, and insert
inside ferrite block.
5. Add insulating material between each end of ferrite block and the PCB, and
secure with Loctite glue.
6. Solder new connector to the PCB and visually check the PCB for stray drops
of solder before reassembling.
7. Switch on the N-20PA and test the connector with a patient sensor.
Caution: Adjust the printer darkness setting until the lightest legible print
is visible. Setting the print darker than this could reduce printer-head life.
Although the N-20PA is designed to automatically compensate for conditions
that might influence the quality of the printout, the user may want to adjust the
print darkness. The normal darkness setting is set at the factory; this setting
maximizes both readability and printer head life.
Note: This procedure cannot be performed after a valid pulse is received
following power-on. Hence, perform this procedure with no sensor
attached to the monitor.
To adjust the printer darkness:
1. Switch on the N-20PA.
Troubleshooting
4-7