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The 4600 Scanner: Which One Of These Is Not Like The Other?

8 Nov, 2002 By: Stephanie Hinz imageSource

The 4600 Scanner: Which One Of These Is Not Like The Other?


Move over HP CLJ 4550 and make room for the new HP
CLJ 4600, Hewlett-Packard's first single-pass color laser printer.
Although consumers have enjoyed the convenience of single-pass
technology for many years with, for example Lexmark's Optra Color 1200,
this new machine is so "user friendly" it virtually eliminates
the need for on-site service.

All four cartridges, the electrostatic transfer belt
(ETB), and the fuser can be removed and installed with such ease that
the service technician may become a thing of the past. Of course, we're
just kidding because despite the machine's clever design, there will
always be a need for talented service technicians ready to tackle the
most complicated machines. Luckily, the training team at Parts Now! was
ready for a challenge when the 4600 came through the door.

Like many single-pass color units, the 4600
uses a transport/transfer belt to feed paper through the path. (See
figure 1, left) However, unlike many single-pass color lasers,
the 4600 feeds paper vertically. Although the paper path is simple and
straightforward, the vertical design is a double-edged sword. The 4600
uses four laser scanners, one for each color
in the machine. (See Figure 2,right)
After discovering this, we were curious to find out what would happen if
we swapped the laser scanners around. Our first thought was nothing, b
ecause all four scanners looked identical and
were assigned the same part number. As it
turns out we were right but not until we discovered what we were missing.

The magenta and cyan scanners were the first
two we swapped. The first test page after the two were switched revealed
a slight alignment problem. (See figure 3, left) At first, we
thought the alignment problem was caused either by bent retaining
brackets that secure the scanners into position or perhaps a missing
screw. These retaining brackets help secure the laser scanners in
position, so if one was slightly bent, it could cause the image to skew.
(See Figure 4a & 4b, bottom right) We determined quickly that
this was not the problem because subsequent test pages exhibited the
same results. Next, we swapped the black and yellow scanners and guess
what? Same issue. So, as the last resort we consulted the only source we
knew that could help us - the Service Manual.

In the chapter that outlines removal and
replacement procedures, we found a note reminding the reader to remember
to put the spacer under the printer frame when replacing the scanner to
avoid skewed images. Was it possible that's what we were missing? Since
we were not replacing a defective scanner, we determined that this
wasn't an option. While it seemed plausible given that shutters on the
laser scanners are triggered open by the toner cartridges, we determined
that it is crucial that the scanners be positioned properly.

One of the greatest challenges we faced was determining whether we had
positioned the scanners correctly because they aren't secured with
screws. This means they have a lot of room to move vertically and
horizontally. As figure 5 demonstrates(left), each scanner sits
in an oval shaped cutout in the metal holding and, for the first time
during our adventure, we noticed that the scanners were not lined up
vertically. We then measured the distance between the left side of the
machine and the position of each scanner and almost all four were
different. Once again, thinking we had found the problem, we centered
the scanners and ran the next few test pages which resulted in - you
guessed it - the same problem.

The deeper we went in the manual, the more we
discovered about the 4600 and the missing link to perfect alignment. The
manual suggests replacing the retaining brackets in the same order that
they were removed (if the right was removed first, replace that side
first and vice versa). In the pages that discuss the machine's
calibration process, HP suggests that calibration be performed whenever
the DC controller, ETB, drum drive motors or laser
scanners are replaced. This had to be it - and it
was. After the machine was put back together for the last time and the
calibration was executed through the "Configure Device" menu,
our alignment issue disappeared. (See figure 6,left) This was
something we didn't consider since the printer automatically calibrates
whenever it is powered on or a toner cartridge is replaced.

In the end, even after the scanner fiasco, we
welcomed the 4600 into our family of printers with open arms. The
simplicity of the paper path as well as its various diagnostic tests
should make this a "tech friendly" machine. However, the
sensitivity and precise alignment of the scanners, makes this machine
unlike any other. Hopefully, these scanners will last the life of the
4600 - but just in case, always remember to center all four scanners
vertically, calibrate the machine after you've replaced a laser scanner,
and a service technician really is a necessity.

Stephanie Hinz is a trainer for PARTS NOW!, a major
printer parts wholesaler for HP, Canon, Lexmark and OkiData. To contact
PARTS NOW! Call 800-886-6688, or visit www.partsnowinc.com. Stephanie
can be reached via e-mail at shinz@partsnowllc.com.


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