7D af issue update , camera back from canon

Started Mar 28, 2012 | Discussions thread
PrimeMover New Member • Posts: 5
Re: Opinions are like...

Boky wrote:

I'll try to explain something to you... but do not feel bad if you can't understand what I have to say -> blame my bad English for that!

I have mentioned already the issues involved with most critical element of AF system -> the AF sensor located at the bottom of the camera body:

1. The AF sensor PCB must be firmly positioned related to mirror - yet, the AF sensor PCB can move freely in all directions. Turn the camera 90 deg to get landscape / portrait photos -> and your AF servo / focusing results will change dramatically. Shake the camera a bit (normal use will do it quite nicely) and the result will be the same. So, the first step is to lock the AF sensor position inside its chamber – I used a bit of araldite.

This is the first bit of rubbish. It is secured very well in every Canon camera I have disassembled. It is very difficult to remove and you will strip the screws unless you have exactly the correct driver. Any component that requires critical positioning is locked in place either with multiple screws and/or with glue that must be dissolved or scraped off if service is required. These components are all attached directly to the mirror box (sensor included) and the mirror box is attached firmly to the chassis. The sensors themselves are individually calibrated using shims to ensure correct focus that is consistent across the frame.

2. The contacts used to transfer the VERY WEEK signal from AF sensor PCB to the camera body main board for processing, are made of copper -> I stated already that this is not good enough -> the contacts will oxidise very quickly, especially if the body is used in dump / cold / near the ocean (sea) environment. The oxide layer will drastically deteriorate the whole AF system performance, because the input variable (electrical representation of what AF system uses to achieve accurate focus) is already very weak…. and is completely useless if the contact resistance is anything but close to 0 ohms. It is possible to solder the ribbon cable that goes from AF sensor PCB to the main board -> but this will complicate the assembly process -> therefore ruining canon profit margins. At least the canon should gold plate the ribbon cable copper ends, AND the socket conntacts where the ribbon cable plugs in the main PCB -> this will prevent oxidation.

This is the second bit of rubbish. While the tracks that make up the flexible ribbon connectors are copper (as are the PCB tacks on all cameras by all manufacturers) which is bonded to kapton and coated to prevent any corrosion. The exposed ends are gold plated (see for example the pictures here that clearly show the gold plated ends) again to prevent any corrosion. Critical signals are also shielded with extra layers of copper. Once they reaches the main PCB they continue along copper traces to their ultimate destination (again just like in every other manufacturers design). Copper is used because it is more conductive than gold. Gold is used only for the connectors specifically because they cant be coated to resist corrosion.

Now, lets us consider the lens….

1. The signal generated by the AF system located inside the body, is sent to the lens to produce the desired rotation of the focusing element. Same noise issues I stated above are fully applicable to the PCB located inside the lenses. Canon had to adopt drastic measures to combat the noise on this PCB -> one look at the noise-suppresing colis imbedded in ferrite should be enough to discard the whole system as comletly incapable of handling low voltage signals.

2. Same story with ribbons and contact -> pure copper prone to oxidation and deterioration of contact conductivity

More crap. I wont go on quoting the rest of you post as it has zero credibility. I have opened every Canon I've owned to do maintenance (Replace worn out shutters. Fix bent CF pins, etc.) I previously serviced cell phones. I can tell you which item has better quality construction (tip it isn't the one that rattles around in your pocket all day).

If you can present credible evidence of any of your claims I'm keen to see it. Will be waiting...

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