Thursday, January 28, 2010

HP LJ 5Si Registration Assembly Teardown

Orientation: For this procedure, 'right end' is the clutch end. The unit is right side up on the bench in front of you.

1) Clutch
>One e-clip.

2) Two Tension Springs

3) Upper Bronze Bearings (6mm bore)
>Two e-clips.

4) Upper Roller w/Flap
>NOTE: Take care not to distort the ground continuity strap at the left end. It's hooked onto the edge of the frame.
>Remove roller from flap.
>Remove gear from roller.
>REASSEMBLY NOTE: Ensure that the clear mylar strip on the flap ends up on top of the roller, not under it, and ensure that the ground continuity strap is hooked back in place.

5) Left End Lower Roller Gear
>One claw.

6) Lower Bronze Bearings (8mm bore)
>Two e-clips.

7) Lower Roller
>It's free of the frame once the two bearings are off,.
>Remove its gear.

8) Scrub gears and bearings with Varsol. Air dry.

9) Clean the rollers with lacquer thinner.

10) Clean remaining parts as required.

11) Inspect/Service the clutch per this article.

12) Reassemble. Check that all screws are snug.

13) Lubricate the bronze bearings with light mineral oil.

Electromagnetic Clutches

The single-plate electromagnetic friction clutch is one of several types of clutch used in printers. Some are permanently assembled units that can't be dismantled for servicing, but many can be easily taken apart, inspected, cleaned and reassembled.

The example I'll use here is the registration clutch in the HP LJ 5Si. It's made by the Ogura Clutch Company. (Their website has a lot of interesting information.)

Characteristics and Failure Mechanisms

The clutches work by applying an electromagnetic field to a steel rotor that forms one face of a disc clutch. When the electromagnet is energized, the rotor becomes magnetized and attracts its mating clutch plate to itself, thereby engaging the clutch.

The clutches are meant to engage instantaneously when energized, and remain engaged with no slippage until de-energized. Typically, the clutches become troublesome when contaminants accumulate on the clutch faces, interfering with prompt, slipless engagement. Symptoms of this are often intermittent. The registration clutch in the 5Si can cause paper jams, misregistration and misregistration accompanied by paper fold-over. Intermittent paper jams are the most common symptom of clutch trouble.

Outright electrical failure such as a winding going open is extremely rare, and easily confirmed, if suspected, by a continuity test with an ohmmeter. The winding of the 5Si's registration clutch has a DC resistance of about 203 ohms. Any given clutch's winding will exhibit some characteristic normal value of DC resistance, depending on its design parameters. An 'open circuit' reading indicates a winding failure -- replace the clutch. A resistance reading significantly lower than normal would indicate an internal short circuit in the winding due to an insulation failure; cause for clutch replacement as well. Again, though, winding failures are rare.

Clutch Service

You'll need a small mechanic's vise to press the clutch back together after dismantling it.

The clutch is held together by two bronze washers that are press-fitted onto the ends of its rotor. Note the following points:

>The washers have a dead flat side, and a slightly chamfered side. The dead flat side goes outboard.

>The washers' outer faces are flush with the ends of the rotor. There is a fair bit of axial play in a properly assembled clutch. That play is normal and necessary.

>Methyl hydrate is a good cleaning solvent here as it leaves no residue whatsoever. The gear is often filthy and needs to be scrubbed with Varsol. Follow that with a methyl hydrate scrub and a blow-off. Never leave the gear to soak in solvent for any period of time.

Pry off the bronze washers and the clutch is apart. Clean the gear as noted above. The magnetic ring on the inner face of the gear is there to cause prompt disengagement when the clutch is de-energized. If it has come free of the gear, replace the clutch. It might be possible to bond the magnetic ring back onto the gear with CA adhesive, but I've not had occasion to try that yet.

Clean the plate, the rotor and the rotor's plastic sleeve bearings with methyl hydrate. (Replacement sleeve bearings are not available; if the bearings are badly worn the clutch must be replaced.) Ideally, your shop should have an air compressor for blowing off components to ensure dust-free assemblies.

When all is satisfactory, press the bronze washers back on one at a time. With the washers on flush with the rotor's ends, you're done. The clutch is fit to go back in service.

Permanently Assembled Clutches

Permanently assembled units are much better protected from contaminant incursion than the serviceable unit dealt with above, but they are by no means 'sealed'.

It's possible to flush them somewhat with a squeeze squirter bottle of methyl hydrate, then thoroughly blow them dry with compressed air. Were that to improve the operation of a suspect clutch, it would at least tell you that the clutch must be replaced.

MONDAY, MARCH 15, 2010

Addendum

'Had a clutch failure last week in an HP LJ 8000; it was the second pass roller's clutch in the paper input unit. It gave quite a set of symptoms:



  • No paper jams, oddly enough, but paper folding noises just upstream of the second pass roller.

  • Affected pages were correctly registered at the leading edge, had a blank band about 3" from the leading edge and were misregistered at the trailing edge (print going clear to the edge and beyond). The blank band area showed evidence of creasing.

The clutch must have been slipping at engagement time, so a sheet's leading edge would be stuck for awhile at the second pass roller while its trailing edge kept advancing. By the time the clutch engagement finally took, the paper had gotten a fold in it, and it got fed through the regisrtation roller and transfer stage that way. On reaching the fuser, the fold would get pulled out flat and the sheet would fuse and exit normally.

I dismantled the clutch and its clutch faces didn't look to be badly fouled, but one of the rotor's plastic sleeve bearings came out with the rotor, suggesting a lack of clearance in the bearing. That may have been adding sufficient drag to cause the clutch to slip.

Monday, January 25, 2010

Repairing Stripped Threads in Plastic

This method does work, but it's not 'instant'. Even though five minute epoxy is the material used, the repair is best left to cure overnight for a reliable result.

1) Blow out the stripped thread with compressed air so it's free of any dust or debris. Check that the screw is clean, that there's nothing stuck to it.

2) Run the screw into the stripped hole to check that the hole is deep enough to accept the full length of the screw, when whatever the screw normally holds in place isn't there. If the screw is too long for that, use a slightly shorter screw of exactly the same diameter and thread pattern for step '5)' following.

3) Mix up a small batch of five minute epoxy. Fill the stripped screw hole with it.

4) Wet the screw with WD-40. The screw must be wet all over but not dripping wet.

5) Run the screw all the way into the hole. Wipe away the squeeze-out and leave it overnight for the epoxy to fully cure.

6) The next day, the screw will be tightly in place but removable because of the WD-40 coating. Unscrew it slowly and you'll have a serviceable thread.

Wednesday, January 20, 2010

Brain Spasms

A technician brought in a LaserJet 4250 this morning. He'd put a maintenance kit in it yesterday, and ever since he'd been getting 13.01 errors -- 'jam in tray 2'.

I looked in the back of tray 2 as the machine attempted a pickup cycle. The pickup roller didn't turn; it just twitched a bit. I pulled out tray 2 and looked in the front; the pickup roller was in the wrong way around. 'Corrected it and the machine worked fine.

And the lesson is, whenever a problem crops up right after you've worked on a machine, RETRACE YOUR STEPS. Had he simply done that, the technician would have had the job done profitably, and spared himself a lot of needless travel.

HP LJ M2727nf ADF Replacement

ADF Assembly P/N CB532-67903.

No tools needed. This is pretty much a no-brainer.

1) Document Input Tray
>Remove the tray from the old ADF unit. The replacement assembly doesn't come with one.

2) Old ADF Assembly
>Swing it up and unplug its connector.
>Lift it straight up with enough force to free its hinge posts.

3) New ADF Assembly
>Remove the orange shipping tape securing its connector/cable.
>Plug in its hinge posts.
>Plug in its connector.
>Open the pickup/feed access cover and remove the piece of orange shipping tape.
>Done. That's it.

Tuesday, January 5, 2010

Lexmark X340 -- Random Notes

Line Interface Unit (LIU) Access

1) Lower Right Side Cover
>One M3x9mm bright washerhead screw in front.
>Swing the cover open and unhinge it.

2) Upper Right Side Cover
>One M3x9mm bright washerhead screw in front.
>Two M3x8mm bright washerhead threading screws at the rear.
>Tug at the lower edge of the cover to unseat it.

3) LIU
>Two cable connections.
>Two M3x8mm bright washerhead screws. NOTE the ground wire terminal that goes behind the LIU at the location of the front screw.
>The large ferrite bead on the two-conductor cable is held in place with mounting tape. Pry it off if it interferes too much with getting the LIU out.

Monday, January 4, 2010

Lexmark E350 -- Random Notes

Service Parts

Fuser: 40X2800

Photoconductor: E250X22G

Pickup Tires: 56P1820

Toner Cartridge: E352H11A -- High Yield Return Program

Fuser Access

1) Tray 1

2) Right Side Cover
>Two claws in front.
>The cover swings open. Pry at the bottom rear to free the hinge.

3) Left Side Cover
>One M3x6mm bright washerhead threading screw in front.
>Two claws in front.
>Swing the cover open far enough and it will pop off its hinges.

4) Rear Cover
>Rear paper tray cover -- squeeze its sides inward to remove it.
>Open rear door.
>Two M4x8mm bright washerhead threading screws.
>Tip rearward and lift the cover away. Note the two hooks at the lower left and right sides that must engage rectangular openings upon reinstallation.

5) Delivery Assembly
>Three M4x8mm bright washerhead threading screws; two at the right, one at the left.
>The item pulls out the back. A bit of persuasion is needed at the left side end.
>REINSTALLATION NOTE: Getting it back in is not so easy; there's a very particular way that it must be tipped to get it started into place. It can be done, but if it gives you too much grief, better to raise the top cover at the left rear a bit -- two M4x8mm bright washerhead threading screws at the top left; one claw just beneath. Raise the cover and the delivery assembly can then be easily got back in place. There's a slight complication to this -- there are tabs on the top cover that must go under the front lip of the delivery assembly. Also, mind the thermistor cable; it can be a little unruly.

6) Logic PCA Cover
>Loosen off four M3x6mm bright washerhead screws.

7) Ferrite Bead
>Unlatch it at one side to open it.

8) Fuser
>Exit sensor cable connection at J11.
>Thermistor cable connection at bulkhead connector on top of fuser.
>AC connection at bulkhead connector on top of fuser.
>One M3.5x6mm bright pan head screw at ground wire terminal.
>Two M3.5x12mm bright pan head threading screws.
>Two latches. NOTE: Two latch levers emerge through the top of the fuser at either side. Each lever end is rounded and has a small hole through it. To remove the fuser, push the levers forward as you pull back on the fuser's frame, one side at a time. It seems to go more easily if you start with the left side latch.
>REINSTALLATION NOTE: Tip the front of the fuser downward as you move it into place. The latches should self-open as they come up against the latch bar and snap into place.

Fuser Exit Sensor Access

Note: The fuser exit sensor is not available as a service replacement part. You can only get one from another fuser.

With the fuser out of the machine, proceed as follows:

1) Exit Roller Gear
>One claw.

2) Exit Roller
>Two swing-latch bearings.

3) Lower Exit Frame w/Sensor
>One M3x6mm bright pan head screw at right side end -- T10 Torx.
>Swing the frame off.

4) Sensor
>One M3x8mm bright pan head threading screw -- T10 Torx.

Configuration Menu

Press and hold 'Check Mark' and 'Back' as you power on.

Diagnostics Mode

Press and hold 'Go' and 'Back' as you power on.

Maintenance Count

There is one. Invoke the Configuration Menu to view or reset it. There's also a photoconductor (PC) count. It can be reset, but not read, from the Configuration Menu.

Lexmark E340 -- Random Notes

Service Parts

Fan: 40X1328

Fuser: 40X4194 (was 40X1300)

Photoconductor: 12A8302

Pickup Tire Pair: 56P1820 (was 40X1319)

Toner Cartridge: 34015HA -- High Yield Return Program

Fan Access

1) Front Door Open

2) Right Side Cover
>One claw high up in front -- triangular pushbutton.
>One claw just above control panel cable.
>The cover swings open. Pry at the bottom rear to free the hinge.

3) Fan
>One cable connection at J18.
>Two M3x30mm bright pan head screws w/captive washers.
>Airflow is outward.
>Cable lay is downward and toward the front.

Fan Lubrication

In a pinch, you can try lubricating a noisy fan.

Get the fan out. On the outboard (wiring) side, there's a blank adhesive 'label'. Peel that off carefully and there's a round vinyl cap that's easily pried out. Flood the cavity revealed with WD-40 and spin the fan and jiggle it axially. Mop up excess lubricant with a Q-Tip and replace the cap. Clean the cap and the surrounding surface with methyl hydrate, dry it and you can re-adhere the 'label'.

Fuser Access

1) Front Door Open

2) Right Side Cover
>One claw high up in front -- triangular pushbutton.
>One claw just above control panel cable.
>The cover swings open. Pry at the bottom rear to free the hinge.

3) Left Side Cover
>One M3x6mm bright washerhead screw in front.
>Two claws in front.
>The cover swings open. Pry at the bottom rear to free the hinge.

4) Rear Cover
>Rear paper tray cover -- squeeze its sides inward to remove it.
>Open rear door.
>Two M3x6mm bright washerhead screws.
>Tip rearward and lift the cover away. Note the two hooks at the lower left and right sides that must engage rectangular openings upon reinstallation.

5) Delivery Assembly
>Two M3x6mm bright washerhead screws; one at UPPER left, one at UPPER right.
>One M3x8mm bright washerhead screw at lower left.
>The item pulls out the back.

6) Fuser
>Exit sensor cable connection at J17.
>Thermistor cable connection at J16.
>Two M3x6mm bright washerhead screws at sheet metal tabs, left and right.
>Pull the fuser out far enough to get at the AC spade terminals.
>NOTE: The spade terminals are a lock-on type that can be quite aggravating to disconnect. The female terminal must be pressed downward to disengage it from the male terminal. You may have to slide back the insulating sleeve to do this. The insulating sleeve on the black wire gets baked and embrittled; you may have to ruin it to get the terminal off.
>REINSTALLATION NOTE: The blue and black wires must lie in their channel at the left side end of the fuser; there's no clearance for them otherwise. Mind the sheet metal tab at the left side end; it's easy to get it in behind its mounting tab, instead of on the outside of it.

Fuser Lamp Replacement

The lamp can be replaced without dismantling the fuser at all.

1) Two M3x6mm bright pan head screws w/captive washers.

2) Withdraw the lamp from the end with the L-shaped lamp terminal. When installing a new lamp, a spring hook is helpful for getting the straight terminal in place.

Configuration Menu

Press and hold 'Select' and 'Return' as you power on.

Diagnostics Mode

Press and hold 'Go' and 'Return' as you power on.

Maintenance Count

There isn't one, but there is a photoconductor (PC) count. It can be reset, but not read, from the Configuration Menu. On the Menu Settings page, under 'Cartridge Information', there's an entry, 'Photoconductor'. It will read 'OK' when the PC count has just been reset.