LASERJET Canon SX Repair Notes

These are some notes collected from my own work and that of readers, regarding common problems with the Canon SX egine as used in the Laserjet II and II series printers, in no particular order.


Just about the most common service message on Laserjet SX engines ( II and III) is the 50 Service error. Here is a great article about what it is and what can cause it. Note, this is an Adobe pdf document.

Parts Now Article


This, from friend Tom:

50 SERVICE: Fuser Error.

Power off printer for at least 10 minutes to clear error. If error is persistent, it's usually caused by a blown AC Power Supply, usually
the triac with the wimpy heat-sink, inside the AC Power Block. Remove access panel on lower right of the printer. Remove metal plate. The bottom row of pins are ODD numbered,  i.e. 1 3 5 7 9 .

Using a DMM, the black lead to the metal chassis, the red lead on one of the following pins normally reads, from left to right:
Pin 1: +24VDC
Pin 5: -5VDC
Pin 9: +5VDC

The DC Power Supply (or Block), right front, gets power from the AC Power Block, right rear. If the corresponding DC voltages are
incorrect, is it a safe bet to replace the AC Power Block. YES.  Remove top cover. Remove AC fan and hood. AC Power Block is beneath the fan, fastened to the bottom and rear chassis with 4 screws.

In rare instances, the AC and DC Power Blocks are both blown, but only if the unit was in a fire, tornado, and submerged in a pond while it was plugged in.


The fuser assembly will lift out by removing the four screws located at the flanges at the left and right ends, Pull straight up and out. It is not necessary to remove printer's the top cover assembly to get the fuser station out.

After many copies the fuser Teflon© coated roller will start losing its coating, and you will see the coating is bubbled or torn when you look into the fuser assembly after removing the wiper pad with the little hinged door open.  The roller is held in place by two cir-clips at either end.  It removes from the assembly from the end which does not have the gear on it, but you have to remove the heat lamp first.  Try to push down on the red silicone rubber roller when inserting the fuser Teflon coated roller to prevent the possibility of scratching it, as the coating is thin and fragile.

The strange angled little bracket with two holes in it goes under the PC board over to the frame end and grounds the PC board to the metal frame.  Consider taking some digital photos of the assembly with a camera or iPad to aid in reference, before taking things apart

It will be necessary to take most of the hardware off on the end which does NOT have the gears, and enough of the hardware off on the side that does have the gears to expose the retainer clip on the end of the fuser metal roller you will be replacing.

The plastic cover shells on the end mount with the black screws which have washers as part of their heads and usually a small smooth shoulder as well, under the head. The wires from the quartz lamp attach with the shiny nickel-colored screws with the wide heads and shoulders under their heads.

Do not touch the quartz lamp, use rubber gloves here.  If you do touch it, clean it off carefully with alcohol. The lamp is withdrawn from the end that has the two-pin connector.

There is a long black lever made of plastic, on a pivot at the end which has the gears and the connector for the lamp. Put the main cover shell back on before re-attaching this lever and its spring.  The big spring goes on this lever (photo to follow) and the small spring goes horizontally underneath it between the spring anchor hook on the left and the metal bracket holding the three gears.

Make sure the lamp is held in the two circular holes which are part of the lamp clips at each end.

The Teflon coated fuser roller is Part No. RA1-3968-CLN (clone) from Printer Works.  The silicone rubber fuser roller that contacts this Teflon one seems to always be OK but you can also replace this at the same time if desired. See Printer Works pages for breakdown and part numbers.

Fuser modules are the same in both the Laserjet II and II models.


There are several styles of DC Controller in the Laserjet II and they are different than those in the Laserjet II although you can make one of the II series controllers work if it's the model RG1-0710.  

-Original production III Series printers had the RG1-1969 DC controller boards in them.  These are numbered in white letters near the edge of the board facing the rear of the printer, in the area where the squirrel cage fan plugs in.  These boards have a bottom pan safety switch on them, which will pop up if the bottom cover is not in place.

-Later original production printers still have the RG1-1969 boards, but the pan safety switch is no longer present.  Originally, there was a bracket with a lever on the plastic end bracket that holds the DC Controller board, which depresses this switch.  If you need to replace an late board with an early board and thus this level and bracket will be missing, just hold the switch depressed with a piece of strong tape.

-Latest (last) III models have a new DC Controller board, which seems, well, a bit failure prone. Part number RG1-2076.  At this writing, summer 2014, no one seems to have these in stock at a decent price.  There are plenty of vultures who rip these boards out of junker flea market and E-waste pile LaserJets, run them under some water in the bathroom sink, and then try to sell them as "Refurbished, Tested" at $ 100 or more.  If it doesn't work when you try it, they will just exchange another one until you get one that works. (If you are lucky.)   Obviously this is not a cost-effective solution.  Stay away from these crooks.   The RG1-1969 boards seem to be available in far better supply and you can use those, they will all sub for the RG1-2076.  But note that an RG1-2076 will not necessarily work in a printer intended for the older RG1-1969 board.  It will only work in printers which contain the RG1-1310 DC Power Supply, so check that number before proceeding.  A fair price from a retailer for any of these DC Controller boards is $ 25.  After all, what could you get if you wanted to sell one of these printers?  Right.  Nothing.


Most of the time this is a problem with the cork separation pad or the pickup tire assembly.  However, friend Tom has some notes on this as well:

Paper Jam: Some paper feed roller assemblies have only one tooth on the clutch (right side of metal rod). The feed roller
has some leeway in it's resting or return position. But if you get paper jams, it might be installed wrong.

Multi-tooth clutches are no-brainers, because there is no adjustment. When the sx printers rev up for a printout and feed the paper
through, a system of two electromagnetically triggered clutches are triggered in a sequence that allows the entire gear carriage to use
only one motor.

So, the front feed roller must return to the proper orientation relative to the separation pad, before  the clutch is engaged and the
roller feeds the paper. The ideal position is with the flat part of the roller facing the separation pad. You can look through the paper cassette hole and see little notches in the two inner plastic wheels just adjacent to the tire itself.  Those little notches should be slightly down but almost facing you.  You must remove the printer shell, the front stabilizer bracket, let the front panel dangle if you wish, and loosen the set screw on the right side of the feed roller rod.

Move the roller to the proper position relative to the separation pad, tighten the set screw, and  either close the lid or stick something in the lid-open detector slot to close the switch until you hear the slight whirrr of the gear carriage initializing position.

Look at how the feed roller is aligned, and if it's correct, or even close, you're good to go.

More notes coming...






Ver. 6/24/2014                 ©Geoffrey C. Fors, all rights reserved