Thermal-pressure motor lock (TPH gear)

Thermal-pressure motor lock (TPH gear)
Difficulty	Intermediate
Duration	90 min.
For series	Z+Any machine released with or after the RZ line, i.e. RZ/RV/EZ/EV/SF/SE and MZ/ME/MF/MH machines.
Tools	Phillips #2 screwdriver (magnetic) Flathead screwdriver Needlenose pliers
Parts	612-10010 1 × TPH gear
Error codes	T19-XXX Thermal pressure motor lock !!System Error!!</br>Press Reset Key</br>If Recovery has Failed, Call Service

This is the draft of an article, it is incomplete or in-progress.

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This tutorial provides step-by-step instructions to replace a broken gear (part no. 612-10010 referred to colloquially as the "TPH gear") in the gear box for the thermal pressure motor—it's used in all Z+Any machine released with or after the RZ line, i.e. RZ/RV/EZ/EV/SF/SE and MZ/ME/MF/MH machines. type machines.

Overview

The thermal pressure system is used to keep the TPHThermal Print Head pressing the stencil material against the write roller, to ensure a clean image is burned. A great deal of force is put on this gearing, and this gear in particular will snap and shatter as the system wears. When it does, the riso will generate T19 or P19 errors and be unable to make a stencil and the whole machine will be locked in "call service" mode.

There is a known flaw in the manufacture of this gear, and the shaft system it sits on. While adjustments were made to the design of this area on some models, broken gears are still being found across multiple machines.

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  A cracked TPH gear—when the collar fully breaks, the gear will shatter or spin freely on the shaft, unable to lift the TPH.

The part can be replaced, but it takes a little while to get enough access to remove it and swap the new one in—this is process is also slowed by the caution required when working with the TPH.

It's recommended that anyone running an RZ or newer machine have 1–2 replacement gears on hand. They are readily available on eBay and AliExpress by searching by the part number 612-10010.

Replacement procedure

The process of replacing this part is a little different between one- and two-drum machines (and depending on the make of your machine you may need to remove some additional covers to get access to things). It will take about 90 minutes the first time you do it (but can be done much more quickly once you know your way around).

Getting into the risograph

First, to access the sections we need, we'll need to pull the MMU (master making unit) out of the machine. Follow the steps you'd take to replace the stencil roll on your machine to get the MMU out (pushing the green button either to the right of the drum removal button on one-drum machines, or on the right side of the riso on two-drum machines).

• For one-drum machines leave the drum in the riso.
• For two-drum machines also remove both drums.

Before you go any further, turn off and unplug the riso. From here on you'll exclusively be working on it unpowered—until the replacement is finished and everything is reassembled.

Accessing the pressure assembly

Replacing the gear requires access to the TPH pressure assembly, the gearing inside the panel with the TPH that is opened up when replacing the stencil roll. The method for getting into this area is different for one and two drum machines.

Removing the gearbox cover on one-drum machines

One-drum instructions

The steps in this section are for machines with one drum only.

The gearbox cover is a metal plate that sits just below the thermal printhead when the TPH is in the open position—usually it has an informational sticker on it explaining that the TPH can be hot and diagrams of how to clean it. It is removed with 4 M3×4 flange head phillips screws (with external hex profile).

• The first 2 screws are accessed with the Master Making Unit Cover in the closed/lowered position, from the left (drum) side of MMU—there is 1 at the front and 1 at the rear, near the hinges at the back of the assembly.
  1. Pull out the MMU if it is not already (the MMU can be manually unlocked if needed—but only if there is no drum sitting on the rails outside the machine).
  2. Remove the first 2 screws.
• The second 2 screws are accessed with the TPH assembly in the open/raised position.
  1. Open the Master Making Unit Cover by using the blue/green plastic handle that runs along the length of it.
  2. Remove the remaining 2 screws.
  3. Slowly remove the loose metal cover (make note that the lower lip of it sits beneath the two tabs that protrude on either side—this is what the first 2 screws were secured to).

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  One of the 2 screws removed from the left of the MMU, while the unit cover is in the closed position.

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  The 2 screws removed while the cover is open (arrows indicate the positions of the previous 2 screws).

Removing the gearbox cover on two-drum machines

Two-drum instructions

The steps in this section are for machines with two drums only.

The gearbox cover is attached in the same way on two-drum machines as on one-drum machines, with 4 screws in the Master Making Unit Cover. However on two-drum machines, because the MMU slides out of the side of the riso, instead of the front—the first 2 screws (those which are removed from the left with the Master Making Unit Cover closed) are inaccessible.

The official procedure in the service manual is to fully remove the MMU however, this is a complex operation that carries with it some risk. Removing and reinstalling the MMU involves manipulating delicate ribbon cables, checking parallelism on its rails, and handling one of the heaviest components in the risograph. There is another way to access the first 2 screws: sliding the MMU all the way to the left, removing the master disposal unit on the left side (a much simpler operation), and removing the screws through the opening that creates.

1. On the left side of the riso, above the paper feed tray, remove the master disposal box.
2. Remove the 5 screws that hold in the large plastic panel around the disposal unit and remove that panel.
3. Unplug the cables connecting to the disposal unit (generally there are two on the right side, depending on the model there may be a third on the left side), as well as any plastic cable guides that are holding the cables on the sides.
4. Tape the loose cables off to the sides so that they are out of the way.
5. Remove the 2 large M4×8 flange head phillips mounting screws in the top left and right corners of the unit.
6. Remove the 2 screws that hold in the plastic panel around the elevator lowering button and remove that panel.
7. The whole unit can now slide straight out of the riso (to the left, when facing the riso from the front/operator's position). Reach in and lift it slightly from inside the area where the disposal box goes, then pull it out.

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  The 5 marked screws secure the plastic panel around the disposal unit.

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  The two cables and small cable guide above them are marked in purple; the 2 screws holding the unit in are marked in green.

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  The paper feed cover is removed with 2 screws (it has two plastic arms at the top corners which hook over the metal shelf).

1. Reaching into the riso from the open door of the MMU area, on the right side, push the MMU all the way to the left side of the riso (first close/lower the Master Making Unit Cover if it is open/raised).
   • The MMU will be blocked at the beginning by a white plastic block at the rear of the MMU—this is normally pushed aside when the MMU door is closed—it can be bypassed by pressing in a small white lever at the rear hinge of the door by hand.
   • The MMU will naturally stop at the end of its track when pushed all the way to to the left.
2. Now the 2 gearbox cover screws (M3×4 flange head phillips screws) can be reached through the left—remove both of them (using a magnetic screwdriver so that they don't fall). If necessary, hold the MMU with one hand so it doesn't slide back to the right.

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  When pressed down, this small plastic hook will free the MMU to be pushed further into the riso.

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  Then press the MMU all the way in until it stops.

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  The 2 screws are on either end of a metal bracket on the MMU.

10. Reaching through the opening from the left, push the MMU back all the way to the right side of the riso (again, it will stop at the end) (the MMU can also be accessed through the openings for drums from the front of the riso).
11. Now pull the MMU out of the riso (as if replacing the stencil roll), and open up the Master Making Unit Cover with the blue/green handle.
12. Remove the remaining 2 screws (M3×4 flange head phillips screws) holding in the gearbox cover, and remove the cover.
    • These 2 screws are removed in the same way as in the one-drum machine instructions above.
    • Make note that the lower lip of it sits beneath the two tabs that protrude on either side—this is what the first 2 screws were secured to—when reassembling later, this plate will need to sit beneath the tabs again.

After finishing the TPH gear replacement, the master removal unit can be reinstalled by reversing the steps used to remove it.

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With the gearbox cover removed, the TPH gear is exposed—it's the bottom gear in the set—likely it will either be fully broken off the shaft or cracked. This is first true confirmation that the gear is in fact the cause of the T19/P19 errors, and needs to be replaced.

Removing the TPH (thermal print head)

Next, the TPH must be removed—the TPH is the single most expensive component in the risograph, so it's important to handle it with care, and use caution in the next steps.

1. Close/lower the Master Making Unit Cover with its handle. Then find the single green cable that runs along right/rear side of the assembly (visible from above), with one end held in by 1 screw. Loosen this screw and free the cable out from beneath it.
   • Depending on where the TPH gear is stuck, closing the TPH assembly this may require a little more force than usual—if it feels like too much force is needed, it can be held partially closed instead, to give access to the screw.
   • Some machines have a small metal bracket blocking access to the screw needed to free the cable—the "Master Making Unit Cover Spacer." This bracket can be removed with 1 screw (M3×6 with hexagonal head).
   • The hook from the green cable sits beneath the washer on the screw that holds it in place—this is a grounding cable, its purpose is to ground the TPH relative to the metal housing it sits in.
2. Open the Master Making Unit Cover again, then remove 2 screws (M3×6) on either side of the blue/green handle to remove the plastic cover around the handle. This will expose the TPH itself.

Never touch the shiny mirrored strip that runs from side to side on the TPH, or the little golden-orange strip above it—these are the actual heating elements of the TPH and are sensitive to oils and abrasives. The rest of the TPH, the round bar, the side panels, the mounting bracket, etc. can all be handled normally.

3. Unplug the two connectors on either side of the TPH—a bundle of purple cables on the left, and a set of black and red cables on the right. The connectors pull straight up and out when the Master Making Unit Cover is in the open/raised position.
4. The TPH assembly is mounted with a pair of hooks that sit around two brass bushings on a small vertical shaft. There is intentionally some play in the movement of the TPH, to allow it to self level when it is pressed against the write roller—so it can turn slightly side to side on this shaft, and move a little up and down it as well.
5. While holding the spring in place, pull the black snap ring off the end of the shaft (popping it out of the groove perpendicular to the shaft), then remove the spring as well.
6. Carefully lift the upper brass bushing up and off the shaft, while holding the TPH assembly down, so it doesn't lift up with the bushing. With it removed the TPH is only being held on by the lower hook on the lower bushing.
7. Grasp the TPH (being careful not to touch the orange/gold strip or mirrored heating elements), and lift it off of the lower bushing—once it is free it will pull away from the shaft.
   • The lower bushing can also be accessed from beneath the TPH—where it can be pushed downwards, out of the lower hook in order to release it.
   • Be careful with the green grounding cable, released previously. The hook of it needs to be wiggled through a narrow opening in Master Making Unit Cover.
   • There is not enough space above the shaft to lift the TPH all the way up and off of it—it needs to be pulled out away from the shaft once the hooks are free of the bushings.
8. Set the TPH aside somewhere safe (not likely to be bumped into or knocked over) with the shiny strip upwards.

• 

  Removing the black plastic snap ring and spring. (The cables are shown connected in this image but should be removed first.)

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  Carefully lifting the upper bushing out of the hook.

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  Finally, the TPH must be lifted off of the lower bushing.

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  During removal carefully free the green grounding cable (the end still attached the TPH is marked here).

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  The removed TPH.

Replace the photographs in this section with ones showing the correct disassembly order (cables first) and add missing images for unscrewing the grounding cable and separating the lower bushing from below, as well as how to hold the TPH.

Removing the TPH support/fulcrum shaft

Now that the TPH is out, it's time remove the support shaft it was mounted on. This will involve two difficult steps—dealing with a pair of very strong springs and removing a pair of e-rings which can be very difficult to handle and get lost easily.

1. Behind the support shaft, on either side, is a large spring (the "thermal pressure spring"). These 2 springs need to be unhooked from their top hooks, then they can be turned off of the levers they were hooked onto on the bottom.

Be careful when removing strong springs—if they snap off unexpectedly they can fly out with a lot of force, damaging eyes/hands/skin. When removing strong springs, always use a hooked or looped tool—something that the end of the spring can't simply slide off of (so not the end of a screwdriver, an allen wrench, or pliers, etc.). A zip tie clicked a few notches in to form a loop makes an easy handle for removing springs.

2. On either end of the TPH support/fulcrum shaft is a large e-ring—both of these need to be removed.
   • Small metal cover panels may need to be removed to get better access to the ends of the shaft, on either side of the Master Making Unit Cover—these can be removed with 1 screw each.
   • See: "how to remove e-rings" for specific advice on dealing with these.
   • E-rings falling into the MMU can be very difficult to retrieve, so be sure to hold a finger tip on them when removing them, or attach a magnet next to them to catch them.
3. Some models have brass bushings on either end of the support shaft, some do not. Remove the bushings if they are present.
4. Push the support shaft to one side to free an end of it, then angle it out.

• 

  The removed TPH support/fulcrum shaft.

Add images for using zip-tie handles to remove the large springs. Also the locations of the e-rings that must be removed (highlighting the extra panels that can be optionally removed for easier access).

Remove the thermal pressure motor assembly

Now the pressure motor gearbox is fully exposed, but it must be removed to swap the gear out.

1. Disconnect the red + black power cable coming from the pressure motor from the pair of purple cables at the white plastic connector where they are joined.
2. Unplug the thermal pressure sensor, by pulling its connector (attached to 3 purple cables) out to the left.
3. Remove the 2 screws (M3×6 with hexagonal heads) that secure the thermal pressure motor assembly, and remove it. Again, be careful of dropping screws into the MMU.

Add an image with the 2 screws circled and the cables indicated.

Replacing the TPH gear

Finally, the gear itself must be replaced. It is screwed into the bottom shaft of the set of three shafts in the assembly—also attached to this shaft are a round, white plastic cam (which presses agains the TPH support/fulcrum shaft to raise the TPH), and a small black detection plate (which, in concert with the sensor in that area, tells the riso whether the TPH is raised or lowered).

The angle at which the gear is reattached is important, as it will make the installation of the springs during reassembly much easier (if followed as outlined below) or more difficult.

1. Place the thermal pressure motor assembly flat on a table, with the gears facing upward, the motor forward, the detection sensor and plate to left and round plastic cam to the right.
2. Remove any residual pieces of the broken gear—afterwards the lowest shaft (that it used to be on) will spin freely.
3. Remove 1 small screw (M3×6 with washers) in the shaft that used to hold the gear in.
4. The plastic cam is similarly held in with 1 screw (M3×6 with washers)—remove this screw then slide the cam off the end of the shaft.
5. Just to the left of where the cam used to be there is a tiny e-ring on the shaft—remove this e-ring.
6. Now the shaft can slide to the left—rotate it so that the detection disc is not passing through the detection sensor, then slide it a little ways to the left—so that it slips fully out of the bushing on the right but is still sitting in the bushing on the left—enough to free up some space in the middle, beneath the remaining gears.
7. Put the replacement TPH qgear in position beneath and to the right of the gear on the middle shaft.
   • The "collar" of the gear should point to the right.
   • Orient the rotation of the gear so that the screw hole in the collar is pointing away from the motor and other gears. (This will result in the finished assembly being partially in the "lowered" position, which will make it easier to reattach the springs.)
8. Move the shaft back to the right, going through the new TPH gear and then back through the bushing on the right side.
9. A groove on the shaft should be exposed just past the bushing on the right. Click the tiny e-ring back into this groove to secure the shaft in place.
   • Snapping e-rings back in is also difficult. See: "how to install e-rings"
10. Place the plastic cam back on the end of the shaft (it is symmetric side to side, and has a "d-profile," meaning there is only one orientation in which it fit in the shaft—there is no risk if putting it on backwards or flipped), then screw it back in place using 1 M3×6 screw with washers (do not over-tighten the screw, hand tight only).
11. Rotate the shaft until the hole in the TPH gear aligns with a corresponding hole in the shaft, then screw it in as well with 1 M3×6 screw with washers (again, hand tight only).

Add images for this section, especially the order of operations and orientation of the replacement gear and location of the e-ring.

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The previous version of this process is documented in old instructions archived below—it still needs to be cleaned up and rewritten for the new wiki. The images from the archived article will be integrated or re-illustrated.

This article is awaiting migration from either the old wiki or elsewhere. Its sources (including archived versions of the original pages) are available here:

1. https://web.archive.org/web/20250810132649/https://www.stencil.wiki/replace-broken-gear-master-making-unit-2-drum-machines

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