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Pentax LX - repair (sticky mirror, MLU, dissasembly, etc)
© Alex Radu     2007-03-04 Categoria: Tutoriale \ Reparatii

This data is provided for informational purposes only. You must assess your ability to perform the operations described. Neither the individual contributor nor assumes any responsibility for damage you may inflict on any camera or other property, or on any person or living creature, by following these directions.

1. Front cover disassembly
  • a. remove screw near the viewfinder (left side as seen from the back)
  • b. remove rewind knob (place a screwdriver in the film chamber and rotate the knob counter clockwise)
  • c. unscrew the three screws depicted and remove the ASA dial
  • d. remove screw under the ASA dial
  • e. remove cover, keep on eye on the gaskets underneath
  • f. unsolder the two yellow wires, as shown (because they are both yellow, I suggest you mark them with a pencil, for later retrieval at reassembly)
  • g. peel off the front leatherette (left & right)
  • h. remove the L shaped metallic part near the DOF preview button (see below image)
  • i. unscrew the four main screws on the front plate (two encircled on the image below, on the left side, two on the right side, not shown)
  • j. leave the self timer lever in normal, un-cocked position
  • k. carefully lift of the front plate a few mm. Don't force it, don't try to separate it from the body, it's still attached by the flash sync cables on the right side (seen from the front). Unsolder them. In case you've forgotten to write down the colours, it's green, brown (both for flash protocol), gray (X sync), light brown (FP sync)
  • l. this will expose the entire front part

2. Solving a tricky problem
the problem is shown below

The gap between the curtains is caused by some sort of malfunctioning of the curtain rollers/tensioning mechanism After performing step 1 (a to l), I've discovered the following issue:

Here’s a closer view:

it seems that the silk string attached to the curtains jumped somehow off the rollers. While the idea isn't a Pentax genuine one (more here:, it's obviously here the culprit for the problem. To fix it, you'll need to put it right back on the rollers. Use your imagination, but try not to use sharp tools (otherwise you'll ruin the strings forever). Try cocking/releasing the camera & gently aligning the curtains. I've finally managed it (after removing the self timer also, but it's not necessary to do so, so I won't illustrate it). Here's how it should have been in the first place:

3. Solving the MLU issue
Both LXs i have had the same problem: MLU was inconsistent. You had to insist to get it done. Here's how i solved it:
- peel off the left leatherete (as seen from the bayonet mount)
- remove the four small screws around the DOF lever

- loosen a little bit the following two screws holding the round plate depicted below

- rotate the plate counter clockwise 1mm approx (if not less)
- reinstall the DOF lever
- check mechanism. Repeat steps as necessary.
- when done, place some sort of sealing over the screws (to prevent them from rotating)

4. the infamous sticky mirror
- official cause? the two rubber dampers shown below

You'll have to replace them both. And the foam near the focusing screen. This is a pretty standard procedure. Finding the right rubber for the dampers & a suitable material for the foam was a little bit tricky.
I've used rubber from a braking pad for a MTBike. It doesn't deform when punched, it still dampens a little bit and it's quite easy to find.
For the foam, try mousepads (closed cell foam). Cut it with a scalpel/x-acto knife.
This will take some time, depending on your skills.

But the story sometimes(!see below) doesn't end here. There's another rubber pad that needs to be removed/replaced. I've decided that removing it is ok. A replacement would pretty hard to do and not vital for the camera's operation.
We're talking about this little fellow here:

It's the damper that brakes the diaphragm actuator. It gets sticky (like the ones in the mirror chamber).

To access it, step 1 (a-l) should be performed. Extra, you will have to remove those 4 screws:

I removed it completely (but I seriously recommend you to replace it with a correct one!) by putting the camera on B & firing the shutter (keep the shutter open). This will expose the screw that holds it in place. It's an eccentric screw (actually a shim around the screw - for adjusting the dampening of the actuator) so marking its position is a good idea.

One LX I have is quite ok with only the two rubber dampers in the mirror chamber replaced. This one had to have its diaphragm actuator brake replaced also in order to function ok. So, if it's not broken, don't fix it. Perhaps you can get away with just the two (simpler to replace).

At the end, of course, you'll have to recalibrate the mirror angle (the small cubic pad shown as a point decides the angle). You can do that by turning the two screws encircled below. I won't elaborate more on this, since it's a tricky operation and some basic repair skills should be present already before even attempting to do it.

© Alex Radu     2007-03-04
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