[Strangways]

I had a 5-15mm suddenly stop focusing, AF or MF. I decided to tear it apart and figure out why.

The flex connectors on the circuit board near the mount, which are easily accessible, were all snugly connected. They don't seem like a weakness that would be likely to fail, so my hopes of a simple repair were dashed.

Going further, I knew I was going past the point where it would be easy to get the lens back together properly. At the very end, making it all the way to the front of the lens, I found the cause: a flex cable that had cleanly broken. The edges are a bit bent, so it broke right where it flexes. It just flexed too many times to survive.

I don't know if Pentax even offers this flex cable as a replacement part, or if it would also need to come with the focus motor, but it's buried so far into the lens that even if you could get the part, the chances of getting it back together properly, and the time required to do so, if you were paying a skilled technician to do it, make it not worth even attempting.

If I have any other Q lenses that stop focusing, I'll do a quick check for disconnected flex connectors on the circuit, but I'm not hopeful, and if they're all connected, I'll consider it a lost cause.

The macro shot of the broken flex was taken by holding the rear lens group of the 5-15mm up to my cellphone's camera lens, using part of the broken lens as a diopter to photograph other parts of itself.

As an aside, I must say I am quite impressed with the tiny mechanism that is the aperture, shutter, and ND filter.

Attached Images

View Picture EXIF

File Date

 

View Picture EXIF

File Date

 

View Picture EXIF

File Date

 

---

Last edited by Strangways; 10-27-2022 at 11:11 AM.

[AstroDave]

I had a 5-15mm suddenly stop focusing, AF or MF. I decided to tear it apart and figure out why.

How did this stop manual focus from working? Unless it got physically in the way and jammed things?

[Strangways]

How did this stop manual focus from working? Unless it got physically in the way and jammed things?

The manual focus ring on autofocus Q lenses is focus-by-wire: it's a digital encoder that sends a signal to the camera body to tell it to send a signal to the lens to activate the focus motor in one direction or another.

For K-mount lenses, the 18-50mm operates this way, as do most (or all - I can't remember for certain) PLM lenses.

[AstroDave]

The manual focus ring on autofocus Q lenses is focus-by-wire: it's a digital encoder that sends a signal to the camera body to tell it to send a signal to the lens to activate the focus motor in one direction or another.

Wow - you learn something new every day. I had to go play with my 02 and 06 - yes, I see - turning the focus ring with the lens off the camera does nothing, and the ring does not have any limits - it will just keep rotating in whichever direction you are turning it. I never noticed that before ('cause I never looked!). Thanks for the enlightenment!!!

My first thought was that this was overly complex, but then I realized the lens maker does not need some kind of additional mechanical linkage system - the motorized focus system is already in there.

[Strangways]

It's a remarkably simple system physically as well. What appears to be the second group, just behind the front element, slides in and out and is actually spring-loaded towards the sensor and infinity focus. The motor pushes it away from the sensor for closer focusing. With the power off, the spring tensions automatically moves it back to infinity, and holds it there so it doesn't flop back and forth when the camera is off or the lens is dismounted.

[c.a.m]

I had a 5-15mm suddenly stop focusing, AF or MF. I decided to tear it apart and figure out why.

Interesting exposé of a forensic tear-down.

Had the lens been used a lot? I wonder what is the life-cycle rating of that tiny flex cable. Seems like a failure point.

- Craig

[barondla]

I had a 5-15mm suddenly stop focusing, AF or MF. I decided to tear it apart and figure out why.

The flex connectors on the circuit board near the mount, which are easily accessible, were all snugly connected. They don't seem like a weakness that would be likely to fail, so my hopes of a simple repair were dashed.

Going further, I knew I was going past the point where it would be easy to get the lens back together properly. At the very end, making it all the way to the front of the lens, I found the cause: a flex cable that had cleanly broken. The edges are a bit bent, so it broke right where it flexes. It just flexed too many times to survive.

I don't know if Pentax even offers this flex cable as a replacement part, or if it would also need to come with the focus motor, but it's buried so far into the lens that even if you could get the part, the chances of getting it back together properly, and the time required to do so, if you were paying a skilled technician to do it, make it not worth even attempting.

If I have any other Q lenses that stop focusing, I'll do a quick check for disconnected flex connectors on the circuit, but I'm not hopeful, and if they're all connected, I'll consider it a lost cause.

The macro shot of the broken flex was taken by holding the rear lens group of the 5-15mm up to my cellphone's camera lens, using part of the broken lens as a diopter to photograph other parts of itself.

As an aside, I must say I am quite impressed with the tiny mechanism that is the aperture, shutter, and ND filter.

Spectacular teardown and tutorial! Great job. Don't remember ever seeing the internal construction of a Q premium lens before. Very interesting. So what are you going to build out of the pieces?

Thanks for sharing,
barondla

[Strangways]

Interesting exposé of a forensic tear-down.

Had the lens been used a lot? I wonder what is the life-cycle rating of that tiny flex cable. Seems like a failure point.

- Craig

I got the lens used so I have no way of knowing. I have an 06 Telephoto Zoom that also had the focus stop working, and I suspect it's the same problem. I'm not overly concerned though: that means 11% of my Pentax Q lenses have had the focus stop working, whereas 66% of my Nikon 1 lenses had their apertures stop working. Small lenses seem to have delicate mechanisms, but some companies did better with their engineering than others!

---------- Post added 10-28-22 at 07:27 PM ----------

Spectacular teardown and tutorial! Great job. Don't remember ever seeing the internal construction of a Q premium lens before. Very interesting. So what are you going to build out of the pieces?

Thanks for sharing,
barondla

I was hoping to swap the front element into a working lens with a scratched front element, but it's an entire group in a housing that is shimmed, and I don't have the equipment to measure and properly shim it if I swapped it over.

[2old4toys]

Hi @strangeways
Can you share as many photos as possible. Yours is the only tear down of the 02 lens published far as I know. I’ve been wanting to extract that shutter mechanism for inspection myself from a good lens. However I fear breaking the good ribbon cable now.

[StigVidar]

So, is this flex cable broken because the lens is used a lot or because it has been stored in the same position for too long?

[Alem]

I have the same problem (I assume, it also stopped focusing) with mi 06. There is no way to replace the flex cable? Maybe some soldering procedure? Sorry if the question is too basic...

[Strangways]

Hi @strangeways
Can you share as many photos as possible. Yours is the only tear down of the 02 lens published far as I know. I’ve been wanting to extract that shutter mechanism for inspection myself from a good lens. However I fear breaking the good ribbon cable now.

Unfortunately I didn't shoot photos along the way. The components are tiny but well made. Getting the rear circuit board and rear group out is easy if you're familiar with lenses. The shutter mechanism is harder, but not impossible. Not something I'd want to try on a working lens just for fun, though. The focusing group? Forget it. If you get it out, you'll never get it back in.

---------- Post added 11-01-22 at 07:22 PM ----------

So, is this flex cable broken because the lens is used a lot or because it has been stored in the same position for too long?

Both could play a factor, though this appears that sitting too long was more of a factor than use, as there is a permanent bend in the cable rather than stress marks. The main cause, however, is just down to how old the lens is.

---------- Post added 11-01-22 at 07:23 PM ----------

I have the same problem (I assume, it also stopped focusing) with mi 06. There is no way to replace the flex cable? Maybe some soldering procedure? Sorry if the question is too basic...

Not only is it difficult to get to the flex cable, it would be difficult to de-solder it from the motor, and difficult to get the lens back together properly, but none of that matters because you can't buy a replacement flex cable from Pentax.

[2old4toys]

Hi @strangeways,
Since it is common fault that only the connection to the focussing motor that died, do you think it is possible to salvage the shutter/no mechanism together with the q lens mount and pcb to repurpose it for cobbling together a legacy lens adaptor for the Q that has working electrical connections to fire the shutter and build in ND control?

[Alem]

Not only is it difficult to get to the flex cable, it would be difficult to de-solder it from the motor, and difficult to get the lens back together properly, but none of that matters because you can't buy a replacement flex cable from Pentax.

I understand. I thought that maybe one could fix the flex cable. But I know almost nothing about this, so I assume is not possible/extremely difficult. And all of it seems extremely difficult. Thank you for your sharing this process!

[Strangways]

I understand. I thought that maybe one could fix the flex cable. But I know almost nothing about this, so I assume is not possible/extremely difficult. And all of it seems extremely difficult. Thank you for your sharing this process!

I've seen lenses from other companies where a flex cable just pops out of a connector, or it uses wires and the solder breaks, all on the circuit board just under the mount. Both are easy fixes. The Pentax lens is better built, so no design flaws that are easy to fix, which just unfortunately means that when a lens fails, there is probably no hope for it. But I do believe they are less likely to fail than many others. There's a plastic post the flex cable rests against, and the end is curved and rounded off so the cable never rests on a sharp edge - it's smart design, probably the best they could do for such a small lens that will always be a bit delicate due to its size.