Repairing and rebuilding the fusers for the Xerox® Phaser® 3635 & WC3550
The Phaser® 3635 and WorkCentre® 3550 models are rather popular multi-function machines. They are still being sold as new equipment for between $1100 and $1600. Pretty soon the fusers will need servicing so let’s get up to speed on this unit. We’ll talk about the various faults which relate to the fuser and then take one apart. Finally we’ll look at how the fuser life counter (HFSI – High Frequency Service Item) can be reset from the control panel. 
Phaser® 3635 Fuser Assembly
The fusers for these machines are given a stated yield of 100 K pages. They are designed to be replaced by a technician. For dealers with machines under contract, repairing the fusers will be one way to keep costs down. For independent repair companies, repairing fusers will be part of the bread and butter of servicing the machines.
When the fuser fails to warm up properly, the machine will show a message “Fuser Error” or “Low Heat Error” and the associated fault codes would be 10-100 or 10-200. For this type of failure, you’d want to check the Fuser Thermostat (thermal fuses) and the Fuser Heat Lamp to see if one of these two components has blown. The fuser lamp / thermostat circuit can be measured at the two larger flat pins on the connector on the fuser’s Inner Face. The fuser lamp circuit should measure less than 2 ohms when the fuser is cold (16 ohms for 220 volt fusers). If the fuser measures “open”, you can also check the two thermostats (thermal fuses) to see if one is blown due to an over-heat condition. They are easy to get to since they’re exposed on the top face of the fuser.
An “Overheat Error” message (10-300) would mean you’d want to check out the thermistor to make sure it’s clean and making good contact with the fuser heat roller’s surface. You’d also want to make sure the machine has sufficient breathing room around it and watch for a failing fuser cooling fan as a possibility.
If the fuser count is nearly up, the machine will give the message “Fuser Warning” (10-500) and soon after “Replace Fuser” (10-510). This message only comes up on the Phaser® 3635 (the WC-3550 doesn’t keep track of the fuser count at all). The fault message and code will persist until you reset the count from the diagnostics. We’ll cover that bit later after the repair procedure.
The fuser can be bought as a complete assembly under the part number 126N00326 for the 110 volt version (or 126N00327 for 220 volt machines). The OEM Parts List also spares some of the parts. They show the Fuser Heat Lamp as 122N00260 for 110 volts (or 122N00261 for 220 volts). The Thermistor is 130N01489, and the Thermostat (double thermal fuse) is 130N01490. The OEM book comes up short, however, on the Fuser Heat Roll, which is unquestionably the most important component in the fuser as far as adding longevity to it. Fortunately, good aftermarket Heat Rolls are available out there.
Now let’s get oriented and see how this baby comes apart. We’ll refer to the “Outer Face” as the face with the yellow warning sticker and the green handles. The “Top” of the fuser then will be the face with the Thermostat (double thermal fuses) and the “Bottom” of the fuser will be the metal plate underneath. We’ll call the geared end of the fuser the “Drive End” and the opposite end will be the “Non-Drive End”.
Fuser Disassembly Procedure:
1. First remove the “Drive End” and “Non-Drive End” Lamp Terminal Covers. Each one is clipped in place. Use a small flat-head screwdriver to release the clips nearest the lamp terminals. In Photo #1 you can see the Terminal Cover on the Drive end outlined in white. An arrow points out the best place to pry to release the clip. Photo #2 shows one of the Lamp Terminal Covers after it’s been removed.
2. You can now pull the spade-lug connectors off of the lamp terminals on either end. Then remove the two screws from the lamp’s terminals and the Fuser Heat Lamp can be gently extracted.
3. Next you’ll want to take the Top Cover off. It is held on by two screws from the top and one from either end. The screw from the Drive End (see Photo #3) and the top screw nearest the Drive End serve to retain a metal bracket, which has two Idler Gears on it. Take that gear bracket off at this point. Now with the 4 screws off you can lift the Top Cover off.
4. You can remove the “Outer Face” cover by pulling down the two green Pressure Release Handles and then releasing the green spring-loaded latch near the Drive End of the fuser, at which point the Outer Cover can pivot out like a door that is hinged on a pair of pins at the Non Drive End. This Outer Cover has the Fuser Exit Roller and the Fuser Exit Actuator on it (Photo #4 shows the top cover off of the fuser).
5. Now you can remove the Fuser Heat Roller. With the Top Cover off, you can simply slide the Heat Roll Drive Gear off followed by the Heat Roll Bearings and Bushings. (Photo #5 shows what the fuser looks like after the heat roll is out. It’s basically just a frame with the two Pressure Rollers).
6. The Pressure Rollers (two of them) will fall right out of their cradles now so watch out for them. They are the kind of roller which has an orange foam-rubber core with a black microsleeve as an outer coating. These will often look wrinkly and twisted and still work just fine for another full cycle without incident.
7. Clean everything up nicely. Re-taping the thermistor’s head with a single fresh layer of Kapton tape is recommended. This helps to preserve the thermistor and also to help protect the new Heat Roller’s surface.
8. Reassemble the fuser. Pay special attention to keeping the Fuser Picker Fingers retracted fully away from the Fuser Heat Roller’s surface when you’re reinstalling the Top Cover. If you don’t do this, the heat roll’s surface is easily damaged. You can use paper clips to hold the Picker Fingers out of harm’s way (See Photo #6).
That’s all there is to it! A very friendly fuser, worthy of a technician’s attention.
Resetting the Fuser Counter (HFSI) on the Phaser® 3635: (Note that no reset is needed on the WC-3550 because it doesn’t keep track of the HFSI counters the way the Phaser model does.)
First enter Diagnostic Mode: For Phaser® 3635, hold down ‘#’ key and press ‘Log In / Out’ while still holding down ‘#’ (If you were entering diagnostics on the WC-3550 you would instead press ‘Menu’ followed by the ‘#’ key). This will bring up the Password Screen. Enter the password ‘1934’.
Now select ‘Service Info’ and then touch ‘HFSI’. A chart with the two HFSI’s which this model tracks will be shown (the fuser and the Document Feed Head are the only two choices). Choose the ‘fuser’ and touch ‘Reset’ followed by ‘OK’. You can also change the ‘max value’ if you want to. Setting the ‘max value’ to ‘0’ will effectively make the HFSI not tracked, meaning the machine will never call for that HFSI again.
When you’re done, press ‘Exit’ followed by ‘Call Closeout’. During the call closeout, the machine will ask if you want to ‘reset counters’. That sounds tempting but you’ll be better off leaving that set to ‘no’ because choosing ‘yes’ will delete all of the fault history for the machine. You may want to refer back to that fault history information at a later date, so leaving it intact makes more sense.
