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Salvaged Circuitry

Olympus 12mm f2.0 Lens Flex Repair

The rear element on my 12mm f2.0 olympus lens was a bit too dirty for my tastes, and I could not get it as clean as I liked with compressed air and a microfiber cloth, so I decided to take the lens apart. The disassembly went smoothly and I was able to remove the metal mount and plastic lens spacer in just a few minutes. This gave me full access to the rear element. There are 4 course threaded screws that mate the stainless steel mount to the plastic lens body assembly and there are 3 very tiny machine screws that retain the rear plastic baffle to the lens mount. There is also one cheeky little machined screw that fastens down the electronic lens connector block to the side of the lens mount.

After initial opening, I saw the one thing that haunts every lens technician: a torn flat flex ribbon cable. It's not uncommon for flat flex cables to run completely throughout a lens, never to be seen again. Roger Cicala posts fantastic teardowns of such lenses on Lensrentals.com. These flat flex cables are not easy to source as a repair part from any consumer lens manufacturer, unless you have an inside man in a lens factory. Often, these ribbon cables are custom cables with varying trace widths and can't simply be replaced with off-the-shelf flat flex cables from digikey or mouser.

Luckily, I just tore the lens mount flat flex cable and no other flex cables. These cables tend to be short and easily accessible, not requiring a complete disassembly of the lens. Most lens mount connector assemblies have a single flat flex cable and mate to the control pcb with a latched fpc connector. Instead, here the mount cable is directly soldered down to the main control PCB instead. This entire PCB has to be removed for this repair process. On closer inspection, the flex pcb has modern edge-exposed pads similar to the castellated pads seen on postage stamp sized Arduino modules or Raspberry Pi Picos. While it is interesting, I do wonder how repeatable edge soldering is on flex pcbs in terms of board rejects. Don't forget to remove the small black ground wire before proceeding with the teardown.

I was debating whether a quick-and-dirty soldering job or a full flex PCB replacement would be a better way to repair this lens. After all, I could simply peel back the polyamide coating on the flex PCB and solder in some 28awg bodge wires. I decided to just redesign the flex PCB instead so there is a replacement part out in the wild. If I made the mistake of tearing this cable upon lens disassembly, there is a good solid chance that other folks will rip this flex PCB as well.

Keeping with the open nature of this repair, this part flex pcb was designed completely in KiCad, a fantastic open source PCB making utility that anyone can download and use. This PCB was designed in KiCad 5.0 and this KiCad file is free for anyone to use. The pad spacing is dimensionally correct, and a caliper was used to measure spacing and trace pitch. Of course, this flex PCB may not be a 100% perfect fit and I will only know when I get the flex PCBs in the mail. I added two positioning holes for the micro four thirds lens communication block as well, to ease in resoldering the lens mount connector. The kicad files are contained in a zip file below.

>>KICAD FLEX PCB FOR OLYMUS 12MM F2.0 LENS<<

In the mean time, I decided to take some tiny gauge enamel coated wire and solder directly to the lens mount connector block. This way my lens had no down time and it's back up in running as my main trusty and bright camera lens. The trick with soldering unknown temperature components is flux every terminal, pre-tin the solder tip, pre-tin the enameled wire and then lightly press all three together very quickly. This way you don't over solder the connector. It is very easy to use too much solder and make the connector a bit melty. This method yields minimal temperature fluctuation in the plastic part and a greater chance of success.

Fits like a glove. All buttoned up and ready for action! Let me know what you think!

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