HP laserjet 45xx schematic

Color

LaserJet

Service Manual Update

4500/4550

The following are updates to the latest version of the CLJ4500/4550 combined
service manual, part number C7085-90921.

Page 14 - The HP LaserJet 4550HDN printer is the base model with a 5 GB hard

Document Summary
 Updates include information that is incorrect or missing in the service

manual.

Author: Deborah Hahn, ICO Technical Marketing

drive, an HP JetDirect 610 print server (network card), a 500-sheet paper
feeder, a duplex unit, and 64 MB of RAM.

Page 18 - Figure 1-3 shows a Serial No. that begins with US. Serial numbers for all
4500/4550 printers models begin with JP. Also, the label has Made in Singapore
listed and the 4500/4550 labels will read "Made in Japan".

Page 120 - Add details on toner level sensing:
How does it work?
The Toner Level Sensor Assembly is mounted to the carousel drive assembly on
the right side of the printer chassis. This PCA provides for continuous toner level
sensing. To obtain the toner level, the printer measures capacitance of the
toner through the developer sleeve, onto the copper plate in the carousel.
Each time the carousel turns, the toner level sensing PCA takes a reading from
the cartridge. The Toner Level Sensing PCA then reports these signals to the
formatter.

How are the readings reported on the Supplies Status Page?
The TLS levels reported on the Supplies Status Page (SSP) are an average of the
raw information that is reported to the formatter. At power-on, the toner level
value listed on the Supplies Status Page is the highest level reported to the
formatter through the first 8 readings taken. After 8 readings have been taken,
a running average of the last 8 readings is reported on the SSP. The running
average continues until the printer is power-cycled, or the top cover is

Page 1of 5

opened. If the printer is power-cycled or the top cover is opened, the printer
doesn't know if a toner cartridge has been changed, so the process starts
over. Due to this averaging the levels reported on the SSP may vary some in
the first 8-10 pages printed, up to 10%.

The accuracy of the toner level sensing PCA is greatest below 70%. Because of
this, the SSP may not report a 100% full level even on a new, full cartridge. A
change to the formula for TLS was made to firmware starting with version

1.009.0. Starting with this version of firmware, at power-on if any of the first 8
readings is greater than 70%, the SSP will read 100%. After 8 readings, a running
average is still taken. If this running average is greater than 70%, the SSP will
read 100%. If the running average drops below 70%, the running average is
reported until the cartridge reaches end-of-life. The SSP will never report levels
between 99% and 70%.

Page 228 - Add 41.X error as follows

41.X

PRINTER ERROR

ALTERNATES WITH

PRESS GO TO
CONTINUE

A temporary printing error
occurred.

X Description

2 Beam detect misprint
error.
4 No VSYNC error.

Press GO. The page
containing the error will
automatically be reprinted.

If this message persists:

1. Reseat the connections
to the Laser/Scanner
and the DC Controller.

2. Replace the
Laser/Scanner.

3. Replace the DC
Controller.

Page 236 - Add 59.0 error as follows

59.0

PRINTER ERROR

ALTERNATES WITH

POWER CYCLE TO
CONTINUE

A fuser motor error has
occurred.

Power cycle the printer to
continue.

If this message persists:

1. Reseat the

connections to the
fuser motor and
Paper Feed PCB.

2. Replace the fuser

motor (M1).

3. Replace the Paper

Feed PCB.

Page 2of 5