HP LJ 1320 -- Separation Pad

Separation pad P/N is RM1-1298.

Replacement is a no-brainer (two prominent screws), but there's a little detail to it that tends to go unnoticed.

Just below the separation pad is a tiny torsion spring that's part of the tray's ground continuity 'wiring'. The upper end of the spring is supposed to bear on the metal surface of the separation pad assembly, not lie underneath it. It should look like this.

Whether this is correctly done or not is really of no consequence, but I thought I'd point it out.

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HP LJ 1320 -- Gear Train Release Link

New fusers for the LaserJet 1320 come with a retrofit kit. The kit consists of a stamped steel link P/N RC1-3670, and a clear mylar insulator. The link's purpose is to link the cartridge access door to the fuser drive, so that opening the door disengages the fuser to facilitate clearing jams.

Included with the kit is a multilingual installation instruction booklet that sets a new standard for wretchedness in corporate technical documentation -- quite an accomplishment. Pay no attention to the booklet, it will only cause bewilderment.

The link is easy to install; it helps if you disengage the white link from the door, but it's not essential to. Don't install the link until the fuser is in place with its gear on it -- the link's presence interferes with installing/removing the fuser's gear. Following are two photographs of an installed link; both show the link in its 'cartridge access door open' position.

Here's the front end of the link.

A 'notch' in the white link pulls the steel link forward when the door is opened.

And here's the rear end of the link where it pulls a gear out of engagement when the door is opened.

You can barely see it, but just ahead of the fan is the clear mylar insulator that's added so the link can't rub two small cables. The insulator comes with pressure-sensitive adhesive on it.

It's not mandatory to install this; I know for sure of at least one guy who doesn't bother with it. What you do with it is entirely up to you.

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HP LJ 1320 -- Fuser Replacement

Fuser P/N is RM1-1289.

This is one of those fuser removals where a whole bunch of seemingly unrelated stuff has to come off/away before the fuser can be removed. Please note the following two points:

a) Items '18)', '19)' and '20)' deal with a cabling trough cover and two cables. Pay close attention to that area as you're dismantling it -- it's a devil of a thing to get back in place correctly at reassembly.

b) New fusers come with a gear train release link P/N RC1-3670. It's a retrofit that links the cartridge access door to the fuser drive, so that opening the door disengages the fuser to facilitate clearing jams. Don't install the link until just before reinstalling the fan. When the link is in place, the fuser's drive gear can't be put back on. See this post for illustrations of the link installation.

Proceed as follows:

1) Cartridge

2) Paper Tray

3) Left Side Cover
- Pry at rear lip. Shift the cover frontward slightly to unhook it.
- NOTE that there's an interlock function associated with this cover. The actuator is a rearward pointing tab high up on the front lip. With this cover removed, the cartridge access door won't close. The interlock is easily cheated with a small screwdriver.

4) Right Side Cover
- Similar to left side cover, but the claws are more tenacious, especially the lower one just below the line cord receptacle. Pry A/R.

5) Rear Cover
- Four M3x8mm black washerhead screws.
- Cheat the interlock for the left side cover and fully close the cartridge access door.
- Stand the machine on its front.
- Open the lower rear door and NOTE how this cover relates to the rear end of the duplexing platform. You'll want to be familiar with that come reinstallation.
- NOTE the two hinge pins for the duplexing platform. The one at the right must be gently freed from the hole in the sheet metal to allow the rear cover to come away.

6) Top Cover
- Three M3x8mm black washerhead screws.
- One M4x10mm pan head threading screw.
- One cable connection at control panel.

7) Formatter w/Shield and Interface Bezel
- Five cable connections.
- Eight M3x6mm bright washerhead screws.

8) Fan
- One wire bail.
- Two M3x8mm black washerhead screws.
- Lay the fan on its top beside the machine.

9) Duplex/Delivery Gear-frame
- NOTE: The gears are free to spill as this item is removed.
- Three M3x6mm washerhead screws.

10) Uppermost Gear (Delivery Roller Gear)
- One claw.

11) Large Fuser Drive Gear P/N RU5-0331.
- One claw.

12) Four Cables at the Extreme Rear
- Disconnect them and free them from their restraint P/N RC1-3667.

13) Cable Restraint P/N RC1-3667
- One tab. Slide the item to your right.

14) Two Remaining Cables at Rear
- Disconnect them and free them from their restraint P/N RC1-3666.

15) Cable Restraint P/N RC1-3666.
- One tab. Slide the item to your left.

16) One Black Wire
- It's at your right. Disconnect it.

17) Two Cable Connections.
- They're at your left. Disconnect them.

18) Fuser Cabling Trough Cover
- The cover is a small, black cover associated with the black, two-wire fuser power cable. Unhook the cover at its inboard rear end and pull it away.
- NOTE: A new fuser will have this cover in place on it. Remove it before installing the fuser

19) Five-Conductor Cable Connection at Inboard Right (There's a big ferrite bead on it.)
- Disconnect it and free it from its channel.

20) Add-On Tray Autoconnect Cable
- Disconnect it and free it from its channel. Pull it in through its grommet.

21) Fuser
- Six M3x6mm black washerhead screws; three at right, three at left.
- Spread the left side vertical chassis member A/R to allow the fuser to come out at an angle.
- AT REINSTALLATION, MIND the wiring at both sides -- it's easily pinched.

22) Trailing Edge Flaps Assembly and Delivery Roller
- These two items are not included with a replacement fuser, and must be transferred over from the old fuser.
- Two claws to release the flaps assembly.
- One swing-latch bearing at the right side to free the roller.

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Feeler Gauge Use

Feeler gauges are one of those seemingly simple things that no one ever says or writes a word about, but there's a bit more to their use than meets the eye.

They're called 'feeler' gauges for a reason -- you 'feel' a gap in a mechanism with them. To do that effectively, you need to be holding only the gauge leaf that's needed in your fingers, not the entire gauge set with one leaf extended.

If you're buying a feeler gauge set, look for one that comes apart easily, like the one pictured below.

Extract only the gauge leaf you need, and you'll have a gauge that will give you a much better feel for the measurement you're making.

Precise 'feel' becomes even more important on an assembly that's relatively yielding, like the carriage of a small dot matrix printer. You're not dealing there with rigid machine parts, as you are when measuring valve lash in an engine with solid valve lifters. A small printer's carriage 'gives' somewhat with little force applied -- a very light touch with the feeler gauge is called for to obtain an accurate measurement. With the bulk and weight of the rest of the gauge set out of the way, it's much easier to apply that light touch and obtain a truer 'feel'.

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Oki 320/1 Turbo -- Printhead/Platen Gap and Parallelism

Parallelism

Parallelism is adjusted by means of a lever-operated cam that raises or lowers the right side end of the front carriage rail. The cam's lever is shown in the following photograph.

Swinging the lever to the right increases printhead/platen gap at the right side end of the platen. Swinging the lever to the left decreases the gap there.

Note the ink daub. That was put there by the factory's technician to indicate the correct lever setting for this chassis.

Gap

Gap is adjusted by means of a screw at the front of the ribbon drive gearcase on the printer's carriage. Its head can be seen in the centre of the following photo.

Note the gear teeth surrounding the adjustment screw's head. Those teeth belong to a ring-gear that's kept engaged with the screw by spring tension from underneath. A short geartrain in the gearcase couples the gap adjustment lever to the visible gear teeth and to the adjustment screw. Here's a view of that.

The ring gear on the adjustment screw can be pushed down out of engagement with its geartrain, enabling gap adjustment to be done independent of the gap setting lever and its geartrain.

The adjustment screw has a left-hand thread, and its action is a bit counter-intuitive. Turning it CW increases the printhead/platen gap; turning it CCW decreases the gap.

Tools

Very little is needed to perform the adjustment; only a small screwdriver, a 0.016" feeler gauge leaf and a bent paper clip for pushing the ring gear down out of engagement. (See this post for some information on feeler gauge use.)

Preparation

Set things up as follows:

1) Printer on a dead flat, hard work surface.

2) Main cover off printer.

3) Ribbon cartridge removed.

4) Control panel removed.

5) Printhead removed, card guide (ribbon protector) removed, printhead reinstalled.

6) Platen knob reinstalled.

7) Forms thickness lever set to position '1' (nearest platen).

8) Change lever in rear tractor feed position (lever all the way forward). (This is to get the friction feed pinch roller pressure off the platen.)

9) Give the platen a couple of turns to ensure that it's at ease in its bearings and all feels right.

10) Parallelism lever at its factory-marked position, or at design centre if there's no mark.

Measuring and Adjusting Gap

When taking a measurement, press down lightly on the front (gearcase) end of the carriage to bias the carriage against the front rail, and ensure that you're feeling the full, true gap. Check the gap at the centre and at both ends, and make gap and parallelism adjustments A/R. (Note that the factory parallelism setting may or may not be quite correct. Feel free to alter it if measurement reveals that it's off.) It's something of a back-and-forth, trial-and-error process. Platen age and condition are a complicating factor.

Platen Condition

Platens don't normally wear in the sense that they 'erode', but they're subjected to continual hammering in use that has the effect of 'compressing' their surface in places. A typical platen that's seen long service will exhibit variations in diameter along its length. The extreme ends of the platen will still be full diameter, but those areas where print was located will be slightly smaller in diameter. All you can do is average it out as best you can. A good practice is to set the gap to a 'snug' 0.016" at the extreme ends -- then the gap over the compressed areas will tend to be a little oversize. Although the gap adjustment is a fairly critical one, it's not as critical as Oki's service and training 'literature' make it out to be. Printers with manual forms thickness adjustment can tolerate quite a bit of platen compression effect with no perceptible effect on print quality or operability.

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HP LaserJet 40X0 -- Paper Feed Guide Assembly Removal

Occasionally, a transfer roller bearing retainer gets broken and the subject assembly must be replaced. The procedure for that is not in HP's service manual. ( The Paper Feed Guide Assembly's P/N is RG5-2643.)

The following procedure removes a couple of items that it's not absolutely necessary to remove, but removing them makes the machine less awkward to work with -- the job goes more smoothly. It's quite a teardown to get at the thing, but it's straightforward. Proceed as follows:

1) Cartridge

2) Tray 2

3) Tray 2 Rear End Cover, if present

4) Fuser End Caps
- Tug their lower edges out and up.

5) Back Door
- Open it and pry at the right side hinge to free the door.

6) Fuser
- Two captive screws.

7) Rear Right Side Cover (Formatter Cover)
- Tug it rearward to remove it.

8) Control Panel Overlay
- Pry at its right side lip to free two small claws.

9) Control Panel
- Pry up its front edge and two claws will let go.
- One cable connection.

10) Top Cover
- Two M4x12mm bright pan head threading screws at the back.
- Two M4x12mm bright pan head threading screws under the toner cartridge access door.
- Cartridge engagement arm -- free its upper end.
- Pry at the right front to free the right front corner.
- Tug the front of the cover up forcefully to free it.

11) Front Right Side Cover
- One claw at the top.

12) Left Side Cover
- One claw high up rear of centre.

13) Tray 1 Door
- Pry gently to free the inner platform from its ways.
- Slide the door rightward off its hinges.

14) Tray 1 Platform w/Sensor Arm Cover and Torsion Spring
- Torsion spring. Later machines have a torsion spring associated with the right side hinge. Free it from the underside of the platform.
- Tug forcefully on the sensor arm cover to pop it off the pickup shaft.

15) Two Black Extended Head Screws near the Front
- The left side screw is visible by the violet cable for Tray 1's paper-out sensor.
- The right side screw is concealed under the envelope feeder's connector cover. Open the cover and you'll see the screw's head.

16) Tray 1 Pickup Assembly w/Left Side Cartridge Guide
- One in-line cable connection for the pickup solenoid.
- One cable connection for the paper-out sensor.
- Five M4x12mm black pan head threading screws in front. Four of them are in deep wells.

17) Paper Feed Assembly
- One in-line cable connection.
- Two M4x10mm black pan head threading screws. NOTE that these are in the upper holes of the brackets. The two lower holes are where two of the Tray 1 pickup assembly's screws go.

18) Cover-Open Switch Bracket
- Three cable connections.
- One M3x6mm bright pan head screw w/captive star washer at blue ground wire terminal.
- One M4x10mm black pan head threading screw forward of and below the previous screw.

19) Registration Assembly
- One M3x6mm bright pan head screw w/captive star washer at the extreme right.
- NOTE. There is another M3 screw forward of and to the left of the previous screw. DO NOT loosen it.
- Five M4x10mm black pan head threading screws.

20) Pre-Transfer Ground Plate
- Tip it up at the right and slip it out rightward.

21) Transfer Roller
- Hook it at the ends and tug upward to pop it out of its bearings.

22) Delivery Assembly
- The left side white bearing unhooks easily and lifts out.
- The right side bronze bearing has a lever on it. Swing the lever up to vertical and the unit can be lifted out.

23) Formatter Cage
- Four M3x6mm bright washerhead screws. (Early machines had a fifth screw at the top.)
- Tug the cage rearward to disconnect it.

24) Formatter Cage Receiver (Sheet Metal)
- Four M4x10mm black pan head threading screws.
- Three M3x6mm bright pan head screws w/captive star washers or washerhead screws.

25) Fourteen-Conductor Cable Connector
- Unplug it and free it from its hook.

26) One M4x10mm Black Pan Head Threading Screw
- It's at the left side, just below and behind the lower rear corner of the fan.

27) Engine Chassis
- It's free to be lifted off the paper tray module.

28) Engine Controller PCA
- One cable connection near the fan.
- Switch Rod -- unhook it at the switch and free its front end from its restraint.
- One ground connection -- the torsion spring end for the drum ground. Free its lower end from a notch in the PCA's sheet metal cover.
- Three indicated M3x6mm dark pan head screws w/captive star washers.
- Four indicated black M4x10mm pan head threading screws. NOTE that there's a prominent
bright screw that remains in place.
- Tip up the fan side of the PCA.
- One fuser power cable connection.
- Nine conventional cable connections.
- One ribbon cable connection.

29) Rectangular Cable Cover at Front Right
- One claw at the right side near the rear.
- Two long-reach claws near the middle.
- One claw at the front -- it's visible and accessible from above.

30) Formatter Cable/Connector Assembly
- One M4x10mm black pan head threading screw.
- NOTE the tab at the rear end of the rectangular underside piece. At reassembly, get that tab in place first, prior to positioning and fastening the main, upper part of the assembly.

31) Main Drive Assembly w/Wiring Harness
- Stand the chassis on its left side.
- Seven M4x10mm black pan head threading screws.
- Lift the assembly straight out.

32) Paper Feed Guide Assembly
- Two M4x10mm black pan head threading screws.
- Tug the assembly forward slightly to free three small studs at its rear.
- NOTE the ground continuity leaf at the right rear of the assembly. It contacts the sheet metal tab's upper surface.

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HP CLJ 2820/30/40 -- Severe Mis-Registration

Symptom: Vertical registration is way off. The paper is getting to the secondary transfer roller far too early. It looks like this.

Cause/Solution: The registration clutch (CL1) is latching up and keeping the registration roller turning when it shouldn't be. Replace the clutch (P/N RH7-5389). Here's a view of the clutch in the machine.

Access:

1) Right Side Cover
- Two M3x8mm washerhead screws in the handgrip cavity.
- Pry at the lower rear lip.
- Pry at an arrowhead at about the middle of the front lip.
- Tip the cover out and lift to remove it.

2) Registration Clutch
- One cable connection. CAUTION: the connector is strongly retained by the clutch's connector at the lower side of the connector's shell. Pry A/R to free the connector without pulling out its wires.
- One e-clip.

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Further Symptoms:

Occasionally, a paper jam or an 'unexpected paper size' indication will occur along with the mis-registration; that's incidental to the mis-registration. The severe mis-registration is the giveaway that the clutch is at fault (latching up).

A machine that's been sitting idle for awhile will likely print a first page correctly. Succeeding pages will show the symptom.

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