Canon 7d – switching off not possible

In fact, this problem could happen to any camera.

I may case i had to repair a 7d which has been dropped down with a flash on it – so the hot shoe contacts were damaged (pulled out from the flex cable, with the half of the flex cable. I tried to repair the flex, but only a 50% result, some flash functions were ok, others not.

We decided with the owner to buy a replacement part for the camera. This is an expensive part, but he has found one on the ebay at acceptable price (a disassembled one, without LCD and contacts – but we needed only the flex).

7d top cover 1

7d top cover 2

As You can see it has been sold in “good condition and works perfectly”. Super. I have go it in my hands, I transferred all the missing parts from the old one to the new one. I pushed the battery in the camera, checked the focusing, exposure, flash – it was ok.

I finished the work, mounted the other parts. At the final check I observed, that the camera works – but I can’t switch it off….

WHAT?!?!?!?

Ok, I tried to find out, if the switch (a slider) is shorted. Not. I mounted back the old one. Swith on/off was ok. I disassembled the contacts. Nothing. The two flex cables were from this point of view pefectly identical.

After a lot of measuring I verified the flex optically under the lupe. And I find something. Then I checked under the microscope. Here is the picture:

IMG_6141  IMG_6146_marked

Measuring again with the ohmmeter – but this time instead of continuity normal resistance.

IMG_6148  IMG_6150

After wiping off the small oxide dot, the resistance was infinite, as normal. The problem with the continuity test is, that multimeters have a preset threshold for open circuit, which is 20-30 ohm….

OK, camera repaired. the problem is, that I have spent 2 hour of labour only because an ebay seller has been lying about the part.

IMPORTANT: in an electronic circuit always check resistance instead of continuity. Camera on/off switches are NOT power switches, they just give a signal to the PCB, so they work on higher resistance too, as the electronic needs only a voltage level to get logic 1 or 0.

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About canonrepair

Ruzsa János. Amatőr fotós, Canon DSLR váz. Amateur photographer. Canon DSLR user.
This entry was posted in 7d, Canon camera, General topics. Bookmark the permalink.

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