Bronze Sleeve Bearing Seizures

An HP LaserJet 4050 came in the shop last week with the complaint that paper was consistently stopping at the registration roller. It turned out there was a good reason for that -- the registration roller had seized so badly in its bronze sleeve bearings that its gear had 'walked' off the end of the shaft a little, and was turning on the shaft to no effect. Here's a photo of the damaged gear.

And here's a view of one of the two bearings that was at fault.

This type of bearing is widely used in all makes and models of printers. Manufacturers love them because they're compact and inexpensive. They're also very durable, but they do require periodic attention, or they'll end up like the bearing shown above.

Seizures as bad as this one are relatively rare, but any machine that's seen lengthy service needs to have its sleeve bearings attended to. Long before a bearing seizes outright, it's likely to squeak and/or add load to the drive motor because it's no longer free-turning. That condition also leads to accelerated wear of gear teeth.

At the very least, apply WD-40 or light mineral oil. When a machine is being overhauled, all of its shafts borne in sleeve bearings should be dismantled, the shafts and bearings thoroughly cleaned, then oiled with light mineral oil on reassembly. (Nylon sleeve bearings needn't be oiled; just cleaned.)

Note that even a seizure like this is not end-of-life for the bearings. If I could get a replacement for the damaged gear, this registration assembly could be dismantled, cleaned, reassembled and oiled for lengthy service yet. Most sleeve bearings will actually last forever with periodic maintenance.

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Addendum -- FRIDAY, OCTOBER 14, 2011

We took a closer look at the 'damaged' gear, and decided that it wasn't too far gone after all, provided that we glued it in place with CA adhesive. (The gear will never have to be removed again for the foreseeable life of the part.) Here's a shot of it after having dealt with the bearings and roller per this post.

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Sensor Toggle Repairs

It's often possible to repair broken sensor toggles with solid copper wire and CA adhesive. Here's a repair made to a narrow-media sensor from a Lexmark T630 fuser.

18 AWG (0.0403" diameter) wire is substantial enough, yet relatively easy to form. Once you have the wire formed and in place, clean the item thoroughly with methyl hydrate, let it dry and apply CA adhesive so it wicks in everywhere between the copper wire and the plastic toggle. Take great care that the glue doesn't get away from you and foul the torsion spring or pivots. Leave the thing undisturbed for awhile for the glue to thoroughly harden.

On reinstalling the sensor, check that your repair's length/shape is ok and tweak it A/R. Here's a view of this sensor back in the machine.

I've done enough of these that I've seen machines return to the shop after considerable service with one of these repairs; this repair method appears to hold up fine.

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HP LaserJet 5 -- Delivery Assembly Overhaul

The upper delivery roller is a weak point -- it tends to glaze and lose traction leading to 'accordian' jams in the back of the printer. Replace both rollers when overhauling an assembly.

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Lower Roller P/N RF5-1077.

Upper Roller P/N RF5-1076.

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1) Upper Black Guide^[1]
- Two claws at the rear corners.
- The front of the guide hooks onto the upper roller's bearing sleeves. Pry gently to free it.

2) Timing Belt
- Slip it off the lower roller's pulley.

3) Lower Roller; Pinch Rollers; Springs
- One e-clip.
- One 5mm bore nylon bearing.
- Slip the roller's bronze bearing out of place to free the roller.
- Four pinch rollers.^[2]
- Four pinch roller springs.

4) Upper Roller^[1]
- One e-clip.
- One 6mm bore nylon bearing.
- Slip the roller's bronze bearing out of place to free the roller.

5) Belt/Pulley Assembly
- One extension spring.
- Lift the tab at the end of the pulley toggle to allow the toggle to turn fully CCW. The entire bracket w/pulley toggle and belt will be free to come away.
- NOTE the small rectangular opening in the lower end of the bracket. At reinstallation, that opening must first go over a mating projection on the plastic body of the unit.

6) Wash and dry (with compressed air) the body, the upper black guide and the belt/pulley assembly.

7) Clean the bores of the two nylon bearings w/methyl hydrate.

8) Lubricate the two pulley spindles sparingly with WD-40.

9) Reassemble with new upper and lower rollers.

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Note [1]: The upper roller has four litle 'riders' on it. They're there to ensure that the trailing edge of an exiting sheet of paper falls away immediately as it exits. When reinstalling the upper black guide, take care to ensure that the riders all point forward as the guide is snapped into place.

Note [2]: The pinch rollers tend to accumulate toner and grime, but it has no ill effect. We don't bother cleaning them.

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HP LaserJet 5 -- Routine Teardown/Overhaul

The LaserJet 5 is an excellent machine -- well worth what it may take to keep one going. Following is the order of work for a thorough teardown and cleaning/overhaul.

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1) Cartridge

2) Tray 2

3) Right Side Cover
- One captive M4 screw at the upper rear.
- Slide the cover rearward a bit to free it.

4) Back Door

5) Top Cover
- Two M3x8mm pan head YZD screws w/captive washers at the upper rear.
- One M3x8mm pan head YZD screw w/captive washers under the toner cartridge access door.
- Tray 1 open.
- Two forward-gripping claws in front (rectangular openings -- 5mm x 17mm).
- Lift cover and tip up its left side.
- One cable connection at the control panel.

6) Tray 1 Door w/Platform Extension
- Pry gently at the inner platform ways to free the door from the inner platform.
- Slide the door rightward off its hinge pins.
- Flex the platform extension A/R to free it from its ways.

7) Left Side Cover
- One claw at upper rear near the front corner of the delivery assembly.
- Pry at the front lip to free it.

8) Right Front Cover
- One M3x8mm pan head YZD screw w/captive washers.
- One claw visible high up.
- One claw visible at the right side.
- One claw below the switch rocker -- accessible via an opening in the sheet metal.
- One claw at the lower left corner.

9) Delivery Assembly
- Ground continuity clip at upper left.
- Two claws low down at rear. Tip the unit up and remove it rearward.
- NOTE the two hooks at the lower front that must engage openings in the sheet metal on reinstallation.

10) Fuser
- Two M4x8mm hex head (7mm A/F) screws w/captive star washers.
- Tug the unit rearward to unplug/remove it.

11) Cross-Brace Below Tray 1 Platform
- Two M3x6mm bright washerhead screws.

12) Tray 1 Platform
- Unhook the torsion spring at the left side hinge.
- Tilt the item downward until it can slip off its flatted hinge pins.

13) Envelope Feeder Slot Cover
- Tug the arrow-marked 'handle' downward to free the cover.

14) Paper Input Unit
- Two cable connectors at the right front.
- Two M3x8mm YZD pan head screws w/captive washers at the right front.
- Three M3x6mm bright washerhead screws at the left side.
- Slide the unit out the front.

15) Memory Access Door
- One captive 4mm screw.

16) Formatter Assembly
- Six M3x6mm bright pan head screws w/captive washers.
- Pull the assembly rightward straight off its connector.

17) Right Side Lower Front Perforated Sheet Metal
- NOTE how this item supports the switch rod at its upper rear corner.
- Two M3x6mm bright washerhead screws.

18) Switch Rod
- NOTE that the longer bent-over end engages the switch in the power supply; the shorter end engages the rocker in front.

19) Power Supply
- Two cable connections.
- Two M3x6mm bright pan head screws w/captive star washers.
- Pull the assembly rightward to unplug it from the fuser AC connector.

20) Printhead (It's self-aligning. No adjustment is disturbed by removing it.)
- NOTE the black plastic shutter actuator at the front left corner of the printhead. The actuator's tip goes behind the shutter's projection.
- Three cable connections.
- Free the cabling from the two upper restraints.
- Four M3x14mm YZD pan head screws w/captive washers.

21) HVPS (The 'Black Box' underneath.)
- Two M3x8mm YZD pan head screws w/captive washers.
- Two claws at the rear.
- Pull the item straight off.

22) Motor
- One cable connection.
- Four M3x10mm YZD pan head screws w/captive washers.

23) Gearbox
- Two M3x6mm bright washerhead screws.
- NOTE: At reinstallation, take care to ensure that this item is correctly and fully seated before running in and tightening the two screws.

22) Right Side Tray 2 Way
- One M3x8mm YZD pan head screw w/captive washers.
- On claw below the fuser AC connector.

23) Left Side Tray 2 Way
- One M3x8mm black pan head threading screw.
- One lock-button. Press it in until the item can be slid rearward.

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24) Blow out the chassis w/compressed air.

25) Reassemble w/replacement parts A/R.

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HP LaserJet 5 -- Top Cover and Control Panel Disassembly

Top Cover

1) Control Panel Overlay
- Pry at right side edge to free two small claws.

2) Ground Continuity Leaf Spring
- One M3x8mm black pan head threading screw.

3) Control Panel
- Two claws at its rear edge.

4) Hinge-Securing Block
- One tab. Lift its rounded end with a tiny hook made from a paper clip.
- Slide the block rearward.

5) Toner Cartridge Access Door
- Free the right side hinge pin, then the left side.

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Control Panel

1) PCA
- Eight M2x7mm pan head YZD threading screws (No. 1 Phillips recess).

The key array is a unit. Note that the 'Go' and 'Job Cancel' keycaps are removeable.

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Lexmark T630 -- MP Feeder Door/Platform Breakage

The Optra S and the T's up through the T640 all have much the same MP Feeder Door/Platform construction, but for some reason the T630's is the most prone to hinge breakage of any of them. We see this often.

A replacement door/platform is P/N 56P1309. Lexmark calls it 'Cover assembly, lower front'.

To remove one of these, open it out to about a 40 degree angle from vertical and tug on it forcefully, using your thumbs as leverage anchors. It will pop free of its flatted hinge pins. Install a new one by forcing its hinges onto the hinge pins' flats.

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Lexmark T630 -- Dusty Biscuit Fans

The small biscuit fan by the fuser at the right side of T630 printers accumulates dust at quite a rate. Here's an example.

This machine only has 18,000 pages on its maintenance counter. We've seen fans much worse than this -- clogged with dust to the point of making a buzzing noise.

Blowing the fan out with compressed air is usually all it takes to restore it to good order. These fans are long lasting and seldom need to be replaced.

Should you need to replace a failed or terminally noisy fan, the P/N is 56P1408; Lexmark calls it the 'cartridge fan'. The fan is held in place by two push-nuts. Coax the push-nuts off their posts with a mechanic's pick to remove a fan.

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