Oki 320/1 Turbo, 420/1 Line Feed Losses

Symptom: The vertical print position on continuous forms creeps upward.

Cause: Worn/damaged gear teeth on the change gear.

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Here's a view of the gear-train.


The rearmost gear (right side of the photo) is the tractor drive gear. Those usually last the life of the printer.

Below and in front of the tractor drive gear is the tandem change gear that provides friction/tractor-feed selection. In front of that gear is the idler gear.

The change gear leads a hard life, and is prone to getting chipped teeth -- random line feed losses ensue. Here's a close-up of a change gear with a missing tooth.

The damage to a tooth needn't be that severe for line feed losses to occur. Even slight tooth damage that can barely be seen will cause trouble so, when the symptom shows up, replace the change gear and the idler gear just in front of it.

Change Gear P/N 51228001.

Idler Gear P/N 51238501.

Remove the reset leaf spring and the tractor drive gear. (One side of that gear's square hub is a claw that holds the gear on the shaft.)

Remove the idler gear and the change gear. (NOTE that the idler's extended hub goes inboard; the change gear's small end goes outboard.) Clean their spindles.

Grease the spindles and the gears' bores liberally. Do not grease the gears' teeth; grease on the teeth will just attract and retain paper dust. Grease the reset leaf spring's working surfaces.

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Wear in the gears' bores will cause the same symptom as damaged gear teeth do. Gear mesh has to be full and flawless for this gear train to work reliably

On printers that have seen long, hard service, the change gear's spindle may be worn, and even new gears won't provide reliable line feeding -- the worn spindle results in marginal gear mesh. The only solution is to replace the chassis. That's actually quite doable, but it does take a complete teardown and transfer of components.

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CA (Cyanoacrylate) Adhesive

Commonly known as Krazy Glue or Super Glue, CA adhesive is indispensable in the workshop. Following are a few brief points about it:

a) It bonds skin instantly. The stuff can be dangerous.^[1]

b) Dollar stores carry it. I've found the dollar store stuff to be perfectly good for my purposes, and considerably less expensive than the brand name products.

c) There's a gelled version available, but I really can't imagine why. One of the adhesive's biggest virtues is that it's extremely runny. It will wick into the tiniest gap or crevice.

d) Runny though it is, it can be made to 'build' with repeated applications. That can be very helpful in the restoration of rusty old machinery; small unwanted crevices can be filled with it. The resultant fill can be filed or sanded, is impervious to water or oil and can be painted.

e) Further to its use as a filler, I've read that you can fill a larger gap with baking soda, then apply drops of CA. I've yet to have tried this myself. I suspect that pungent fumes result when it's done. Some types of applications result in fumes, and this is likely one of them.

f) It's not terribly heat resistant. LePage's website advises that immersion in boiling water can soften cured adhesive, so it's likely unsuitable for any application that will subject it to temperatures approaching 100° C. That said, you can safely use it as a threadlocker, or for any machinery assembly application that may need to be taken apart again. Just as with threadlockers, sufficient heat will soften it.

g) Its water and chemical resistance is impressive. I've read that acetone will soften it. Apart from that, though, the stuff seems to stand up to just about anything.

h) Keep it in the fridge. Heat, light and humidity all tend to thicken it. Kept in the fridge, a tube of it will stay fresh and runny; you'll get the use of all of the tube's contents.

i) I've read that if it gets on cotton, it generates a lot of heat as it sets, enough heat to be dangerous.

j) There are many specialized versions available, but you have to go to industrial supply houses for them. So far, I've gotten by fine with the common variety. There's much more information about the material available on the web.

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Note:

[1] There's a flipside/upside to this.

If you're plagued, as I am, by splits in fingertip skin through the winter months, CA adhesive is a therapeutic. The instant you acquire a fingertip skin split and notice the attendant pain, seal the split with CA adhesive. The pain stops. The split is cleanly sealed against infection and can heal from beneath undisturbed.

I've read that some individuals may find the adhesive irritating and consequently useless for this, but it works for me.

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HP LJ 2420 Gear Kit P/N KIT-24xx-GR-NN

The kit consists of three gears:

1) Narrow, rearmost 19t gear P/N RU5-0379.

2) Wide, upper-frontmost 21t gear P/N RU5-0377.

3) Lower-frontmost 20t gear P/N RU5-0378.

Item '3)' is the one that leads a hard life and wears out, making for a noisy gear train.

Each gear is held on its spindle by a claw -- they're easily removed. Replace all three. Grease the teeth. Lubricate the spindles with WD-40.

HP LJ 2420 Fuser Access

The 2420's fuser is not user-replaceable, but it's not difficult to get at and replace.

There's a set of three gears that should be replaced whenever a fuser is replaced. You have full access to them once the fuser is out. The set of gears is P/N KIT-24xx-GR-NN. See this post for more infromation.

Proceed as follows to remove the fuser:

1) Tray 2

2) Rear Cover/Door Assembly
> Pull the rear door fully open.
> Two M4x10mm pan head threading screws.
> Two claws within the tray 2 cavity.

3) Mains Receptacle Bezel
> Treat as if hinged at its outboard long edge.
> There’s a single downward-hooking claw about 3 3/8" below its top edge. If the item is stubborn, slide a thin tool in behind it about 4" below its top edge and move the tool upward. You’ll unhook the claw.

4) Black Plastic Cover at Left Side (Your right.)
> One claw/latch -- it has a ‘handle’ extending rearward.
> Pull the cover toward you. A spring hook is helpful.

5) Fuser Power Cable
> It's at the lower right just below the line cord receptacle.

6) Exit Sensor Cable (Violet)

7) Thermistor Cable (Yellow and white.)
> Free the cable from its white restraint. The restraint can be unlatched with a fingernail or a small screwdriver.

8) Duplexer Input Ramp
> Two claws -- they have ‘handles’ extending rearward.
> Push up on the claw handles and pull the ramp toward you.

9) Fuser
> Three prominent M4x10mm pan head threading screws.
> One M3x6mm pan head screw w/captive star washer. It’s in a recess at the fuser’s lower right.
> Tug on the power cable and the green wheel to coax the fuser out the back.

HP LJ 1320 -- Flashing Amber LED; Motor Doesn't Run

A flashing amber LED on the 1320 can mean any of several things, but when the motor doesn't run at all it's a giveaway that the cover interlock switch is not being made. The interlock actuator is a rectangular plastic projection at the upper-left corner of the toner cartridge access door. The projection is about 5/8" long, long enough that it's a bit fragile and easily bent over rightward by a careless user.

In the instance we encountered, we were able to bend the projection back to straightness without it breaking off.

Terminology -- Circuit Boards

The terminology in this industry is a bewildering mess of ill-conceived and sloppily applied terms. Nowhere is that more evident than with respect to the major circuit boards typically found in laser printers. I'll attempt to clarify the subject here.

First, though, we need to clear away some clutter.

The terms 'board', 'circuit board', 'logic board', 'printed circuit board (PCB)' and 'printed circuit assembly (PCA)' all mean the same thing -- a thin, flat, usually rectangular piece of insulating material with conductive traces and electronic comonents and connectors on it. I'm partial to 'PCA' (Printed Circuit Assembly), and in writing I always use that term following a circuit board's name; e.g. Formatter PCA or DC Controller PCA. With that out of the way, let's get on with engine controllers and formatters and system boards and the like -- they're the source of much confusion.

Early Days -- The LaserJet II and Lexmark 4019

In any monochrome printer, there are two distinct functions at work. One is engine (mechanism) control; the other is page composition.

In the LaserJet II, engine control was done by the DC Controller PCA; page compositon was done by the Formatter PCA.

In Lexmark's 4019, the engine control and page composition functions were combined on a single PCA -- the System PCA.

Engine Control PCAs

HP has been fairly consistent with the use of DC Controller PCA for the engine control PCA's name.

Lexmark has made models with separate engine control and page composition PCAs. For those machines, Lexmark uses the term Engine Controller PCA, not DC Controller PCA.

HP uses the term Engine Controller PCA as well, but they reserve its use for PCAs that have the engine control function and the power supplies combined on them. Many of HP's modern crop of compact machines are constructed this way.

Formatter PCAs

Formatter PCA continues to be HP's term for a page composition PCA.

Where Lexmark has made machines with separate engine control and page composition PCAs, they've used the term RIP PCA for what HP calls a Formatter PCA. 'RIP' stands for 'Raster Image Processor'. (If you're familiar with the operation of CRT displays, you'll certainly recognize the term 'raster'. Laser printers employ rasterization as well.)

Main Logic PCA

'Main Logic PCA' is liable to mean System PCA or Formatter PCA or RIP PCA. It's a term that's best avoided, really, but it does crop up.

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Lexmark T-Series 500-Sheet Tray Teardown

This procedure gets you access to the electronics and the pinch roller drive/tensioning mechanism.

1) Upper Front Paper Guide
- One M3.5x8mm pan head threading screw.

2) Light-Coloured Upper Front Face (T64X Only)
- Four M3.5x8mm pan head threading screws from underneath.

3) Autocompensator Assembly
- NOTE the relationship of the paper out sensor flag to the actuating stud on the arm of the autocompensator. The stud goes under the curved ramp on the flag.
- Two cable connections.
- Three M3.5x8mm pan head threading screws.
- Unhook the retraction spring.
- Lift the item away.

4) Paper Out Sensor Flag
- Rotate it back a bit and it can be lifted out.

5) Electronics/Mechanism Box
- Two M3.5x8mm pan head threading screws at upper front and rear (not present on later units).
- Four M3x15mm pan head screws w/captive washer (T10 Torx recess).
- Two M3 nut plates.
- NOTE: At reassembly, don't bother putting back the two lower screws -- they're just a needless nuisance.
- Pass-Through Sensor -- dismount it and free its cable from its restraint slot.
- Two claws -- one high up in front; one low at the rear. The front one is easily accessible. Free the rear one by inserting a 1/4" slot screwdriver and rolling it to push the claw forward.
- The box is now free to be lifted out.

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