HP Laserjet 4 Manual

High Voltage Power Supply Assembly  
The High Voltage Power Supply Assembly provides the necessary
voltages for the printer’s electro-photographic processes. The
+24B VDC supply is used to power the High Voltage Power
Supply Assembly. A summary of the major components of the
high voltage system, is given in the table below (see Figure 7-18
for High Voltage PCA layout).
Checks Action
Are the connectors for the Primary
Charge roller, Drum Ground, Developing
Bias, Toner Level Sensor damaged,
corroded,...

Interface Troubleshooting
This section provides an overview of the printer interface
requirements. Refer to Chapter 3 for detailed information about
the printer interfaces and configuration.
Communications Check 
NoteCommunication problems are normally the
customer’s responsibility. Time spent attempting
to resolve these problems may not be covered by
the product’s Hewlett-Packard warranty.
The Customer Service Center (CSC) is available
to the customer to help them through these
problems. The CSC...

AUTOEXEC.BAT Standard Configurations 
Parallel DOS Commands   
If the previous check did not produce the desired result, ensure
that the AUTOEXEC.BAT file contains the following statements
for parallel interface communications:
MODE LPT1:,,P
For MS-DOS version 4.0 and above, enter:
MODE LPT1:,,B
NoteThis example assumes that you are using parallel
printer port LPT1. If you are using LPT2 or
LPT3, replace LPT1 in the example with the
appropriate printer port.
If the problem persists, proceed to Table 7-30...

Communications Checks
Checks Action
Is your computer configured to the
parameters described in the
configuration instructions?These parameters are required to
communicate with the printer. Verify your
computer’s communications port
configuration matches these parameters.
Note: If these parameters are not set
properly, they may yield a 40, 20, or
22 ERROR on the printer’s Control Panel.
For Serial Communications only
Does the printer’s baud rate match that
of the computer’s communications port?Run the...

If the host system and printer still are not communicating, and
steps 1 through 9 have been completed, replace the Formatter
PCA and the MIO card, and reconfigure the printer.  If the
problem persists, a protocol analyzer may be needed to find the
source of the problem.
CautionHP LaserJet printers are not designed to work
with mechanical switch-box products without
proper surge protection.  These devices generate
high transient voltages that cause permanent
damage to the Formatter PCA.  This
circumstance...

MIO Troubleshooting
The Self Test Printout and explanation shown on the following
pages contain valuable information regarding the current status
of the MIO. Before attempting to troubleshoot a network problem
or notifying your network consultant of a problem, always obtain
a Self Test Printout.
Troubleshooting Hints
The JetDirect Card Status Block (see Figure 7-10, status block 2)
indicates the functionality of the JetDirect Card. An I/O NOT
READY STATUS indicates a problem. A 2-digit error code...

Explanation of Self Test Printout
1Multiple Environment Information. General information
about your JetDirect MIO.
2JetDirect Card Status. I/O CARD READY indicates the
interface is correctly configured and capable of
communicating. I/O CARD NOT READY indicates there is a
problem with the interface, configuration, or server.
3Network Statistics. A list of network statistics is generated by
the JetDirect MIO. All statistic counters are reset to zero
when the printer is turned OFF.
Supported Network...

Figure 7-10 MIO Staus Information on the Self Test Printout
7-58 Troubleshooting 

Troubleshooting Aids
Component Locations
The following illustrations help you quickly find the parts
discussed in this chapter. 
12
3
4
5
5B
5A
5C
Figure 7-11 Major Assembly and Connector Locations
Number Part Number Part
1 Fuser Assembly 5 Paper Feed Assembly
2 Cooling Fan 5A Paper Control PCA
3 DC Controller PCA 5B Sensor PCA
4 Main Motor Assembly 5C Paper Pickup Motor (M2)
Table 7-31
Troubleshooting 7-59 

12
3
4
5
6
Figure 7-12 Major Assembly and Connector Locations (2 of 3)
Number Part
1 Laser/Scanner Assembly
2 DC Controller PCA
3
Interconnect PCA Assembly
4
Paper Control PCA
5 High Voltage Power Supply PCA
6 Exit Sensor Assembly Table 7-32
7-60 Troubleshooting