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Upgrading the HP LaserJet Series II to a LaserJet III

My HP LaserJet Series II
I bought my HP LaserJet Series II back in 1989. At that time, computers were not the commonplace household items they are nowadays, and laser printers even less. However, when a friend of mine working for HP offered to grant me his employee rebate, I went for it. Even with the rebate, the deal still put me back almost 4500,- DM altogether, since I also bought a memory upgrade (without which the printer was unable to print an entire page at 300dpi graphics resolution) and the Microsoft Z Font Cartridge required to print text at in the fancy Times Roman typeface in 12 and 14pt. Out of the box, the printer only provided two fixed pitch typefaces, unworthy of a laser printer in my mind.

The LaserJet III
The LaserJet Series II turned out to be a huge success for Hewlett Packard, motivating many of its competitors to release compatible models at a lower price tag. I remember a friend of mine buying a QMS P800 printer at about the same time, which never worked reliably on complex page layouts due to PCL (the “printer control language”) emulation compatibility issues. He eventually replaced it with a LaserJet III, the follow-up to the series II model that left the competition behind and clearly established HP’s supremacy in the printer market. The LaserJet II addressed many of the shortcomings of its predecessor: It came with 1MB of RAM, enough to print an entire page in graphics mode, and substituted PCL 4 by PCL 5, which while still maintaining compatibility with PCL 4, provided significant improvements such as scaleable fonts and GL/2 graphics commands. Both improvements were quite spectacular when compared to the LaserJet II’s only supported bit-mapped fonts, which required to be downloaded to the printer for every type face, slant, size or orientation. With the revised III model, the font could be downloaded as a vector typeface, scaled to the required size by the printer. The HP LaserJet III was even able to place text at an arbitrary orientation, or fill the font outline with a pattern. The printer came with 8 scaleable fonts, in addition to the three bitmap fonts required for PCL 4 compatibility, eliminating almost entirely the average user’s need to buy additional fonts.

But there was more: The LaserJet III came with a feature called REt, which stands for resolution enhancement technology, and does exactly what it says. Exploiting the printer engine’s intrinsic horizontal 600dpi capability by placing additional dots in between the 300dpi raster at edges, the printer output for text and GL/2 images approached that of a 600 dpi printer.

What is most amazing about all this, however, is that the LaserJet III’s improvements over the series II model were entirely due to a largely improved firmwire. The SX engine remained the same, down to the power supply, fuser and every other component. In fact, HP only redesigned the main controller board to accommodate for the bigger firmware, and made a few simplifications, such as a switch detecting an open bottom cover being replaced by a wire, or a few internal diagnostic LEDs no longer soldered in.

The first LaserJet III controller board built upon the same 10MHz Motorola 68000 CPU its predecessor used. A first revision brought down cost by using higher integrated circuits and more SMD parts, and the second revision eventually introduced a 16MHz CPU, speeding up data processing considerably for complex pages, or when using the Postscript cartridge. The picture shows the revision 2 board of the LaserJet III (left) next to the LaserJet II board.

The Upgrade
In 2006 I learned all this and more from The Printer Works, including the hint that a LaserJet III board performed flawlessly when transplanted into a series II model. When I was given an old and defective LaserJet III in the spring of 2007, I decided to give it a chance.

Replacing the controller board is very simple. After removing the toner cartridge, font cassettes and paper tray, I turn the printer upside down and remove the dozen or so screws holding the bottom cover in place. Removing the bottom cover reveals the large image controller board to the left, and a smaller DC controller board to the right, above the fan (this is a good opportunity to clean the fan, if required). The controller board is held in place by eight screws, two of which establish contact with the 5V DC power terminals on the DC board. The board is plugged with a two-row connector onto the DC board, and a second connector attached to a cable leading to the front panel. The III board has the same dimensions and connectors and easily fits in the same location.

While the LaserJet series II has a single memory extension slot, the LaserJet III has two of them. Since the LJII case only provides one opening, any secondary memory extension card must be installed before reassembling the case, as it becomes inaccessible afterwards. Note that you cannot reuse your LJII memory cards: HP slightly modified the pin assignment (the picture shows my old LaserJet II memory board with 1MB installed to the left, and the newer board with 4MB for the LaserJet IIIto the right. Both are third party boards). I was lucky to obtain a LaserJet III with a third party 4MB memory card installed, however I was unable to fit it through the LJII’s opening, since my board is slightly higher than the slot. If inserted before remounting the bottom cover, however, the board fits nicely, provided the two plastic tabs were removed prior to inserting.

Cold Reset
After reassembling the printer, I was disappointed to see an error #50 message on the front panel’s display. This usually means that the fuser or power supply is faulty, which of course could not be the case for my machine, since it worked flawlessly before the board swap. The fuser is connected to the DC board, and the connector is known to fail intermittently after such a long time of operation. A little contact spray here and there solved the issue. Some people report that bending of the contact clips was necessary to re-establish reliable electrical contact. That would have been my next step.

It may be necessary to perform a cold reset on the printer by keeping the Online and Enter buttons pressed when powering on the printer. This resets the printer to factory defaults, but was unnecessary for my machine. A “05” printer test showed that everything worked fine, and confirmed that the 4MB memory extension card was well detected. The next thing I did was test the Postscript cartridge I had recently bought for little money, which took a little longer to boot but also worked fine. Considering that PCL5 provides many of the advantages of Postscript, I haven’t decided yet if I use the cartridge on a regular basis or not. Note that the 33439Q PostScript cartridge exists in two versions, with only the later revision being compatible with the second revision LaserJet III board. HP put a little blue dot sticker on the back of the revised postscript cartridges, as seen in the picture to the right.

The page counter
The HP LaserJet II and III keep track of the number of pages printed. My series II engine has carried out about 38000 print jobs, while the new board indicates some 58000 pages: The page counter is implemented on the controller board by means of an EEPROM.

While HP has thoughtfully adressed this issue by implementing a service mode, which allows to pre-set the page count number, I was afraid that the EEPROM on my new III controller might be damaged, as the new board's counter seemed stuck and refused to increment.

I still gave the service mode a try, and it worked out successfully: After pre-setting the page counter to the 38540 pages my engine had printed with the old board, the replacement board resumed incrementing. Service mode is entered by keeping the On Line, Continue and Enter keys of the LaserJet's control panel pressed while powering on the printer. Upon the blank display, pressing Continue followed by Enter will put the printer into service mode, which will be indicated by all four control panel LEDs being lit, and the display showing "SERVICE MODE". After a few seconds, the usual 05 Self test will be performed, and the LEDs turn off. As soon as the printer is tested and warmed up, the display will again show the "Service Mode" message, accompanied by the green READY LED.

Service mode allows a number of other Test operations, which are indicated in the service manual. It is better to not mess with these operations, though. The page counter becomes accessible after pressing the Menu key. The page counter is indicated as a six digit value, with the leftmost digit underlined. This digit can now be modified using the + and - keys. Once the correct value is entered, the value is confirmed with the ENTER button, and the underline cursor will move to the next digit. After the sixth digit has been entered, the printer resumes service mode. Service mode can be left by pressing the Online button. I recommend to print a few pages and to carry out a 06 Self Test, which will print out the test page indicating the new page count.

next: ...LaserJet Service Error#50 (and what do to if it ever happens to you)

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