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HP 8550 Service Manual - Page 218

Logarithmic correction and BGR->YMC conversion, Logarithmic Correction

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Logarithmic correction and BGR->YMC conversion A Logarithmic Correction The output of the CCD has linear characteristics in relation to the light reflected by an original. However, the density perceived when looking at an original does not necessarily have linear characteristics. Figure 106 shows the relationship between the density of an original perceived by the eye and the output of the CCD. Figure 106. Original density compared to CCD output To correct the discrepancy, the copy module performs a level conversion as shown in figure 107. Figure 107. Density level conversion 216 Chapter 5 - Theory of operation EN

Section	Page
Contents	5
Figures	7
Tables	19
Product information	23
Introduction	25
Copy module	25
Features	25
Specifications	26
Overview	28
Automatic document feeder (ADF)	30
Features	30
Specifications	31
Overview	32
Side high-capacity input (side HCI)	34
Features	34
Specifications	34
Overview	35
Model and serial numbers	37
Safety and regulatory information	37
Declaration of conformity	37
FCC regulations	38
Service approach	39
Service approach overview	41
Parts and supplies	41
Ordering	42
Obtaining related documentation and software	42
Ordering consumables	43
Ordering FRUs	43
Parts exchange program	43
Technical assistance	44
List Server	44
HP ASAP	44
HP FIRST	45
Dealer Response Line	46
HP Software Distribution Center	46
HP Direct	46
Customer Support Sales Center	46
Parts identification	46
Customer Information Centers	46
HP Customer Care Centers (CCC)	47
Warranty	48
Operational overview	49
Control panel	51
Copy module functionality	53
User mode	54
Automatic gradation adjustment	59
Cold reset	59
Original-set indicator (ADF)	60
Warnings and actions	60
Self-diagnostic messages	61
Service mode	62
Overview	62
Navigating service mode screens	65
Copier, display mode (DISPLAY)	67
Copier, I/O mode (I/O)	79
Copier, adjust mode (ADJUST)	85
Copier, run/check mode (FUNCTION)	95
Copier, machine settings (OPTION) mode	100
Copier, test print mode (TEST)	110
Copier, counter mode	113
Feeder	116
Adjustments and maintenance	119
Overview	121
MFP print engine adjustments	121
Parts unique to the HP LaserJet 8550MFP print engine	121
Adjustments unique to the HP LaserJet 8550MFP print engine	122
Copy module adjustments	123
End-user adjustments	123
Mechanical and electrical adjustments	124
Required adjustments when replacing parts or upgrading	131
Upgrading and localizing the copy module firmware	137
ADF adjustments	142
Mechanical adjustments	143
Electrical adjustments	157
Replacing the DADF controller PCB	160
Side HCI adjustments	161
Gap between the printer and the side HCI	161
Base plate position	162
Paper-size change (A4 or letter)	163
Periodically replaced parts	165
Cleaning	166
Cleaning by an end-user	166
Cleaning by service technicians	166
Solvents	166
Cleaning parts on the copy module	167
Cleaning ADF parts	169
Cleaning side HCI parts	175
Lubricating	176
Theory of operation	177
Introduction	179
Notes on the power switch	179
Copy module	180
Functional construction	180
Outline of electrical circuitry	181
Inputs to and outputs from the major PCBs	182
Basic sequence of operations	185
Sequence of operations during copying	187
Copy module exposure system	190
Scanner home position sensor and operation	192
Scanner motor	193
Controlling the scanning lamp	195
Identifying the size of originals when copying from the glass	199
Copy module image processing system	202
CCD	203
CCD driver	204
AP-IP (analog image processing) PCB	205
Digital image processing	208
Control panel	234
Fan	236
Power supply	237
ADF	246
ADF electrical circuitry	246
Communication with the copy module	247
Inputs and outputs to the DADF controller PCB	248
Basic operation	251
Functional overview	252
Picking up originals	258
Reversal operation	263
Reduced page composition	265
Delivery operation	268
Detecting originals	271
Controlling the pick-up motor	277
Controlling the belt motor	279
Detecting jams	281
Improper placement of originals	284
Power supply	287
Motors, solenoids, and sensors	288
PCBs	289
Indicator PCB	290
General timing charts	290
Side HCI	306
Pick-up feed system	309
Power supply	316
Sensors	317
Solenoids and motors	318
PCBs	319
List of variable resistors (VR), LEDs, check pins by PCB	320
Input and output signals to the deck controller PCB	323
General circuit diagram	326
Removal and replacement	329
Required tools	333
Repair notices	334
Copy module	335
Identifying the external covers	335
Removing the lower front cover	336
Removing the upper right cover	336
Removing the upper rear cover	337
Removing the upper left cover	337
Removing the rear cover	338
Removing the upper front cover	339
Removing the scanner motor	340
Removing the scanner motor driver PCB	341
Removing DIMMs on the reader controller PCB	342
Removing the control panel	346
Removing the LCD assembly	348
Removing the flexible cable	355
Removing the scanning lamp and scanning lamp heater	359
Removing the standard white plate cover	365
Removing the intensity-detection PCB	366
Removing the lens-mount cover and CCD unit	367
Removing the electrical unit pullout	369
Removing the reader controller PCB	372
Removing the ECO-2 PCB	373
Removing the AP-IP PCB	374
Removing the copy module main power supply PCB (DCP1)	375
Removing the accessories power supply PCB (DCP2)	376
Removing the power supply cooling fan (FM4)	377
Removing the inverter PCB unit	378
Automatic document feeder (ADF)	379
Identifying external covers	379
Removing the ADF	380
Removing the body cover	382
Mounting the original-width detecting volume	385
Removing the pick-up motor unit	387
Removing the ADF motor unit	389
Removing the belt motor	391
Removing the clutch unit	394
Removing the delivery motor	396
Removing the pick-up roller	398
Removing the separation belt unit	400
Removing the feeding roller unit	401
Removing the registration roller	404
Removing the delivery/reversing roller	409
Removing the delivery roller unit (bottom pick-up mode)	416
Removing the delivery roller unit (top pick-up mode)	418
Removing the reversing guide	421
Removing the stopper plate solenoid	424
Positioning the paper-retaining plate solenoid (SL2)	426
Positioning the paper-deflecting solenoid (SL3)	428
Removing the stamp solenoid	429
Removing the feeding belt	433
Side HCI	436
Identifying the external covers	436
Removing the upper left cover	437
Removing the front cover	437
Removing the rear cover	438
Removing the upper right cover	438
Removing the pick-up unit	439
Removing the pick-up roller	442
Removing the feed roller and separation roller	443
Removing the lifter wire	444
Removing the lifter motor (M1)	454
Removing the feeder motor (M2)	454
Removing the pick-up motor (M3)	455
Removing the deck controller PCB	455
Removing the power supply PCB	456
Troubleshooting	457
System-to-device troubleshooting	459
Pre-troubleshooting checklist	459
Process of elimination	460
Copy module troubleshooting	462
Overview	462
Necessary adjustments for replaced parts	462
Image fault troubleshooting	464
Image faults	478
Numbered error codes	495
Faults not identified by error codes	521
Using the copy module service mode to test parts	528
ADF troubleshooting	530
Fault isolation	530
Numbered error codes	531
Self-diagnosis	535
Check the output of the DADF controller PCB	536
Side HCI troubleshooting	537
Overview	537
User and service LEDs	538
Sensor and switch tests	540
Test pick-up	541
Faults not identified by error codes	543
Parts and diagrams	549
How to use this chapter	553
Printer parts unique to the HPColor LaserJet 8550MFP	554
Stand	557
Screw/ring kit	557
Stand assembly	558
Copy module	560
Screw/ring kit	560
Belt kit	561
Gear/pulley kit	562
Spring kit	562
Assembly location diagram	563
External covers and panels	564
Internal components	566
Power cord terminal assembly	572
Control panel assembly	574
Copyboard cover assembly	576
Mirror assembly 1	578
Electrical tray assembly	580
Dc power supply PCA	582
APC power supply PCA	584
Noise filter PCA	585
Control panel PCA	586
Control panel CPU PCA	587
Control panel inverter PCA	588
Reader controller PCA	589
Analog image processor PCA	590
Motor driver PCA	591
Inverter PCA	592
Connectors	593
ADF	602
Belt kit	602
Bushing kit	603
Gear/pulley kit	603
Pin kit	604
Screw/ring kit	604
Spring kit	606
Assembly locations	607
Mounting hardware	608
External covers and panels	609
DF assembly	610
Document tray assembly	614
Upper cover assembly	616
RF assembly	618
Right paper delivery assembly	632
Paper feed motor assembly	634
Belt drive motor assembly	636
Upper paper guide assembly	638
Lower paper guide assembly	640
Separation roller assembly	642
Paper separation assembly	644
RDF controller PCA	646
Connectors	647
Side HCI	651
Bushing kit	651
Gear/pulley kit	651
Screw/ring kit	652
Spring kit	653
Assembly locations	654
Mounting hardware	655
External covers and panels	656
Internal components	658
Lifter drive assembly	665
Paper pick-up assembly	666
Deck controller PCA	670
Connectors	671
Numerical parts list	674
Alphabetical parts list	682
Index	713
A	713
B	715
C	716
D	720
E	722
F	722
G	724
H	724
I	725
J	726
K	726
L	726
M	728
N	729
O	729
P	730
Q	733
R	733
S	735
T	739
U	740
V	740
W	740
X	741
Y	741