Pentax ZX-5n Mirror Motor Gear Replacement

Written By: Sam Gustafson

Comments: 9

Pentax ZX-5n Mirror Motor Gear Replacement

Difficulty

Difficult

Steps

Time Required

2 hours

Introduction

A common failure of the Pentax ZX/MZ cameras is the Mirror Motor Gear. The gear drives core functions of the camera including the shutter and mirror movement. If it fails, the shutter will no longer fire and the mirror will be stuck close in the up position.

This guide explains how to disassemble the camera to access the Mirror Motor Gear as well as how to install a new gear. A general understanding of how cameras work is recommended. Some technical soldering is also required.

Tools

Parts

Pentax MZ/ZX Mirror Motor Gear

Step 1

Push down on the screw to depress the spring loaded hinge and release the door.

Step 2

Remove six 5.3 mm #00 screws.
Remove one 3.4 mm #00 screw.
The short screw has a machine thread and screws into the plate underneath. The rest screw into the plastic body.

Step 3

Remove three 5.3 mm #00 screws (the bottom-most screw is not always present).
Remove one 7.3 mm #00 screw.
Remove the remote trigger cover.

Step 4

Remove one 3.4 mm #00 screw.
Remove two 5.3 mm #00 screw.
Gently lift up on the flash housing to help remove the cover if necessary.

Step 5

Remove two 3.9 mm #00 screws.

Step 6

Slide the eye cup up and off to access the screws underneath.

Step 7

Remove two 5.3 mm #00 screws by the eyepiece.
Remove one 6.8 mm #00 screw in the battery compartment.
Remove one 7.0 mm #00 screw near the take up spool.

Step 8

Lift the cover so it is just free of the body. It is still attached by several wires.

Step 9

Use a 1kΩ-10kΩ resistor to discharge the capacitor. Place the resistor between the blue wire, exposed in the previous step, and ground.
The flash capacitors store energy at a very high voltage. Failing to discharge the capacitors properly could result in personal injury and/or damage to the camera.

My camera doesn't have the same yellow connection point (is it apart of the camera or your own). I was wondering if there was any other way to discharge the flash capacitors? And how do I know when I've completed the step, any sound cue? Thanks in advance.

tarek tarek -

The yellow piece you see in the picture is a resistor covered in heat shrink tubing. When you discharge the capacitors, you are making a connection between the high voltage pin and ground, which allow the energy to flow out. The resistor is there to slow the current and have a safer discharge. If you don't have a resistor in the range listed, picking something higher will still allow a safe discharge but it will take longer. With a 10 kOhm resistor, it usually takes about 10 seconds to fully discharge. I check the voltage with a meter to make sure it's at a safe level. There isn't really an audible or visual cue to know whether it has discharged.

Sam Gustafson -

Step 10

De-solder the green, blue, brown and black wires from the flash PCB.

When soldering the connections, what temperature would you recommend?

tarek tarek -

I'm not sure what the optimal temperature is. My soldering iron is set at 380 C but that might be a little on the high side.

Sam Gustafson -

Step 11

Move the top cover to the side to access the battery connections. It is still connected by a flex cable.
De-solder the indicated joints. Use a solder sucker on the tabbed connections.
Pull the black wire from the battery flex to get more slack in the connection to the top cover.
Be careful not to overheat the flex circuit. Work in short durations. Allow for cool downs in between if necessary.

Step 12

Desolder the flex cable connecting the top plate to the camera body.
Be careful not to overheat the flex circuit. Work in short durations. Allow for cool downs in between if necessary.
The top cover can be completely removed at this point.

Step 13

Use a solder sucker to de-solder the four posts from the flex circuit.
This is the most difficult part of the repair. Patience and persistence are required.
Be careful not to overheat the flex circuit. Work in short durations. Allow for cool downs in between if necessary.

A small remark. Having tried to use a "regular good" solder sucker to remove solder, it sucked in the pin connecting the two flexible boards along with the solder. Apparently, I heated the soldering spot too well. The remaining solder was successfully removed with the Goot CP-2015 wick.

Stepan Koloskov -

It is very easy to reflow the solder on the green PCB and knock the pins out of position. They are very conductive. But I haven't sucked one up yet, haha. Solder wick is good solution.

Sam Gustafson -

Step 14

De-solder the marked connections.
Be careful not to overheat the flex circuit. Work in short durations. Allow for cool downs in between if necessary.

Step 15

Remove one 4.3 mm #00 screw.

Step 16

Gently pry up the plastic carrier under the flex circuit. It may catch slightly on the battery contact tab.
Pay close attention to the connections around the four through-hole posts as you lift the flex. Make sure that no solder is left over and that it pulls away freely.
This metal tab is lightly held in place with lacquer and can easily come loose. Keep an eye on it.

Step 17

Remove one 3.3mm #00 screw.
Remove one 3.9 #00 screw.
De-solder the red wire.
Peel off the black tape. Leave it attached to the wires.

Step 18

Gently peel the flex circuit from the surface of the capacitor.
There may be additional adhesive underneath the larger capacitor.
Lift the two capacitors and the flash PCB out as a single unit.
The double sided tape used to secure the capacitors can be softened with isopropyl alcohol if necessary.

Step 19

Remove two 3.4 mm #00 screws. Remove the plate holding the contacts in place.
Peel tape from the plate. Leave the tape attached to the flex circuit.
Remove the flex circuits from their retaining studs.

Step 20

Remove one 3.3 mm #0 countersunk screw.
Remove one 3.9 mm #0 shoulder screw.
Remove four 3.3 mm #00 screws.
Pull a little slack through the housing on this flex cable.
Pop the plate off its posts, rotate slightly clockwise and pull gently through the loosened flex cable.
To the camera tech that left me a happy little note...I see you.

Step 21

It's best to remove these parts now so they don't fall out later on in the repair.

Step 22

Remove one 3.8 mm #00 screw.

Step 23

De-solder the connections.
Lift the flex off the retaining studs.
Be careful not to overheat the flex circuit. Work in short durations. Allow for cool downs in between if necessary.

Step 24

Remove two 5.3 mm #0 screws.

Step 25

Remove two 7.4 mm #0 screws.
Remove one 8.3 mm #0 screw.
Remove one 3.3 mm #00 screw. The metal bracket will be loose and should be removed as well.

Step 26

Push the front housing block slightly up then lift the left side up and away from the housing.
Proceed slowly and watch for any components that are catching. The right side is still attached by a large flex cable.

Step 27

There may be shims at the mounting points of the front housing block.
Note the positions and remove if loose.

Step 28

De-solder the black wire.
Remove four 3.7 mm #00 screws.
Detach the buzzer from its mounting posts. Use isopropyl alcohol to soften the lacquer if necessary.

Step 29

Grab the motor and gently wiggle the plate loose.
If it feels stuck, move the sliding plate down, towards the bottom of the camera

Step 30

De-solder the red and black wires.
Remove two #00 screws.
Use the lettering on the motor to note its orientation. If installed or wired backwards, the motor will spin in the wrong direction.

Step 31

Pull off the old gear.
Press the new gear on until about 1 mm of the shaft extends past the end.
If it is too difficult to press on, use a soldering iron to heat the brass gear. A small amount of thermal expansion should make it easier.

Step 32

The green and yellow gears can sometimes slip off their posts while working with the motor.
Check that the alignment holes are properly synced before installing the mirror motor assembly.
Aperture set lever spring. Note this part for installation of the mirror motor assembly.

I think it would be necessary to add in what position the mirror is in this photo.

Stepan Koloskov -

If the green gear is engaged with the drive lever, the mirror should be in the down position. But the position doesn't matter too much at this point. It's really only step 35, when the mirror box is reinstalled that it needs to be down. I'll try to add a couple more photos next time I do this repair.

Sam Gustafson -

Step 33

Disengage latch so the slide bar can move freely.
Move the slide bar about half way down its total travel.
Let the latch snap back into place so the slide bar is held in the new position.
This ensures that the aperture set lever spring couples properly with the slide bar during reassembly.

Step 34

Install the mirror motor.
Place the left side first. Then swing the right side in, coming up and under the spring loaded lens release.

Step 35

Rotate the grey gear downward until the mirror is in the charged/down position.

Step 36

Push the shutter charge lever upward. You should see the shutter blades move as you do this.
The second picture shows the shutter in the charged position. It may already be in this position and not need charging.

Step 37

Gently place the front assembly block. Work it into place until the back of the block is flush to the back of camera.
Proceed with the rest of the re-assembly, following the guide in reverse.

Conclusion

To reassemble your device, follow these instructions in reverse order.

Author

Sam Gustafson

Member since: 02/09/22

4686 Reputation

One comment

Grazie è semplicemente perfetto

pietro mariani -