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The HP CLJ4600 and 4650 Printers: Similar on the Outside, but Much Different on the Inside

6 Oct, 2004 By: Steve Geishirt imageSource

The HP CLJ4600 and 4650 Printers: Similar on the Outside, but Much Different on the Inside

A few
months ago, HP introduced an upgrade of the CLJ4600—the CLJ4650. As most of us
have come to realize over time and trial, an upgrade of a machine that appears
similar to its predecessor typically is similar with the exception of some extra
bells and whistles.

is not always true, though. An example supporting both thoughts is the upgrade
of the LJ4000 to the LJ4050 and then to the LJ4100. The LJ4000 and LJ4050
utilize the same print engine and run at 17 pages per minute. The LJ4100,
however, runs at a higher speed of 25 ppm. Even though most of the part layouts
were nearly identical, the number of parts that interchange between the LJ4100
and its two “ancestors” are next to nil. Once the page per minute is changed in
a printer, many other things are altered electronically and mechanically.

this article, I will focus on some of the key changes in the CLJ4650 and its
predecessor, the CLJ4600. First, I want to point out the consumables and supply
parts that are interchangeable between the two machines. These items include:

  • Black Toner Cartridge

  • Cyan Toner Cartridge

  • Yellow Toner Cartridge

  • Magenta Toner Cartridge

  • Tray 1 Pickup Roller

  • Tray 1 Separation Pad

  • Tray 2 Pickup Rollers

are two parts that are not on this list, but apparently work in each of the
printers—the ETBs (Electrostatic Transfer Belts) and laser scanners. HP provides
separate part numbers for both of these CLJ4600 and CLJ4650 components. HP
indicates in the service manual that these parts are specific to their
individual model. I have noted in the past, however, that HP will come up with
new parts and new part numbers for items that will function just fine on the
older models.

I do
have reservations, though, on the laser scanners. One major difference between
the CLJ4600 and CLJ4650 is the fact that the CLJ4600 uses ImageREt 2400 to
create an enhanced 2400 dpi image while the CLJ4650 uses ImageREt 3600 to create
an enhanced 3600 dpi image. While both of these units did function in each
machine, when it comes to the fine details the laser scanners may not be able to
accomplish what they were specifically designed for if they are not on the
correct machine. The bulk of ImageREt 2400 and 3600 is done in the formatter
board. Slight tweaks to the optics in the laser scanner can make a world of
difference for those customers who have good eyes for the fine detail. In time,
I’m sure we’ll be able to more accurately determine the differences and make a
good decision. Until then, keep your customers in mind and put the correct laser
scanner in the correct printer.

interchangeability of the other units listed above comes in handy not just for
ordering purposes, but also for troubleshooting. It’s great to take the ETB or a
toner cartridge out of a CLJ4650 and temporarily use it in a CLJ4600 to
trouble-shoot a problem. But this is where many of the consumable items stop in

Remove the cover of each printer and you wouldn’t even think there is a
difference. Start changing around parts, though, and you’ll notice right away
that there is an absolute disparity. The fuser, if placed in the wrong machine,
will cause a 50.4 error. This is due to a pin configuration change in the
connector that creates an open connection in the thermoswitch.

those of that believe all you need to do is somehow modify the connection, the
drive gear to the fuser has also changed. The CLJ4650 now has a helical (twisted
tooth) gear while the CLJ4600 has a standard spur (straight tooth) gear. It’s
obvious that the fusers won’t interchange. (See Figures 1 and 2)

issue with the helical gear does not stop at the fusers, however. The CLJ4650
cassette trays also contain a helical drive gear while the CLJ4600 has a
spur-type drive gear. So interchanging paper trays is not feasible. Another
CLJ4650 part that now uses a helical drive gear is the paper pickup assembly,
which restricts interchange.

seems to be a theme here with the helical gears and non-interchangeable parts.
The addition of the helical gears is likely to keep technicians from
accidentally mixing up parts and putting them in the wrong machines where they
will not function correctly, if at all. This would save troubleshooting and
technical support time.

Another interesting change to the CLJ4650 is the new memory HP placed in it.
(See Figure 3 and 4)

CLJ4650 only has two DIMM slots, and the memory comes in 200 pin DDR (Double
Data Rate) memory DIMMs. The DDR DIMM sizes come in 128 MB, 256 MB or 512 MB.
The CLJ4650 printers have a max memory of 544 MB. Not only is DDR memory a shift
for HP’s LaserJets, but HP has now incorporated three card slots to the

the old HP II and III font cartridges? They look a lot like those except about
1/10 of the size with a metal casing. They are not accessible from the outside
of the printer. The whole formatter needs to be removed to access them. The
first slot is the firmware and it is labeled as such on the formatter, thus
memory slots are truly memory slots. The other two cartridge slots are available
for “font cards or third party solutions,” according to the CLJ4650 data sheet.
Third party solutions could include, for instance, an option such as the Duplo
booklet maker. These solutions can be found at

Basically, the CLJ4650 is not a simple upgrade as most would assume by just
looking at the covers. Some of the nifty upgrades are big changes such as
ImageREt 3600, the new DDR memory and font cartridge slots. I’m sure we’ll be
seeing more of each of these upgrades as other new products roll out into the

bad news for those of you stocking parts that assume the CLJ4650 parts will
probably interchange with the CLJ4600 components is that few components actually

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