HP Laserjet 4 Manual

1
2
3
4
Figure 7-13 Major Assembly and Connector Locations (3 of 3)
Number Part
1 Power Supply Assembly
2 Envelope Feeder Main Motor (M4)
3
Lower Cassette Drive PCA
4
Lower Cassette Main Motor (M3) Table 7-33
Troubleshooting 7-61 

Figure 7-14 Switch Locations 
Number Part
SW101 AC Input ON/OFF Switch (Power Supply Assembly)
SW 601 Top Cover Open Sensing Switch
SW602
TEST PRINT Switch
SW603
PC (Tray 2) Tray Size Switches
SW604
SW605 Table 7-34
7-62 Troubleshooting 

Figure 7-15 Optional 500 Sheet Lower Cassette
Number Part
SW851
Optional 500 Sheet Paper Feeder Paper Tray (Tray 3)
Size Switches SW852
SW853 Table 7-35
Troubleshooting 7-63 

5VR202
J206
J203
J204 J205 61 181 1 7 12
1
3
1J202
J201
13
1
3J212CP202
16TB201
CP201J211
4110 1J2103 1
J2094 1 3 125 26
J213 J208 J207
Figure 7-16 DC Controller PCA Layout—LaserJet 4/4M
Number Part
J201 Paper Control PCA
J205 Scanner/Beam Detect
J206
Laser Drive PCA
J207
Formatter PCA
J208 Deliver/Exit Sensor PS3
J210 Interconnect PCA
J209
Cooling Fan
J211
Main Motor
J212 Power Supply/Fuser Drive
VR202 Registration Adjustment
TB201
DC Voltages (from Power Supply) Table 7-36
7-64 Troubleshooting 

5
J20415 1
1 92
1
J206J205 VR201
1
1331
17 J201
J21231J215
TB201 6 1J214
10 1J21331
J2113 J2101 81
1
7
J209J208 J20731 32
Figure 7-17 DC Controller PCA Layout —LaserJet 4 Plus/5
Number Part
J201 Paper Control PCA
J208 Scanner/Beam Detect
J209
Laser Drive PCA
J207
Formatter PCA
J210 Deliver/Exit Sensor PS3
J213 Interconnect PCA
J211
Cooling Fan
J214
Main Motor
J215 Power Supply/Fuser Drive
VR201 Registration Adjustment
TB201
DC Voltages (from Power Supply)
J206
Control Panel Table 7-37
Troubleshooting 7-65 

TB403 TB404
TB405
TB406VR401
J402 3
1
J401
5
1A
B A
B TB402 TB401
Figure 7-18 High Voltage PCA Layout
Number Part
J401 High Voltage PS Connection To DC Controller PCA via
Interconnect PCA
TB401 Transfer Roller Contact
TB402 Drum Ground Contact
TB403
Toner Low/EP Toner Cartridge-in-Place Contact
TB404
GND
TB405 Developer Roller Contact
TB406 Charge Roller Contact
VR401
Factory Adjustment Only Table 7-38
7-66 Troubleshooting 

Repetitive Defect Template  
Repetitive print defects usually are associated with a specific
roller within the printer, or the Toner Cartridge.  The following
templates are provided to help quickly isolate the cause of
repetitive print defects.  Align the first occurrence of the defect
with the top of the “ruler”, and measure to the next occurrence of
the defect to determine the roller in question.  When you are
certain that your defect pattern matches the pattern of the
template, replace the indicated...

Figure 7-20 Main Wiring Diagram (LJ 4+/5 only)
7-68 Troubleshooting 

Voltage Test Points  
The operating voltages of the printer can be verified by:
1Listening for the exhaust fan. A rotating fan indicates that the
+5 VDC and +24A VDC voltages are present. (The fan runs on
+24A VDC.  The +5 VDC enables the +24A VDC.)
2Listen for the Main Motor.  If the Main Motor runs, the +24B
VDC is enabled, therefore +24A VDC must be present.  
Measuring the DC Voltage Levels 
The DC voltage levels can be measured directly on the DC
Controller TB 201. TB 201 connects the DC Controller...

7-70 Troubleshooting