Canon DSLR – mirror not working ERR20


The camera was a 60d, but in fact could be a 40d, 50d etc. – any camera with two motors.

Symptom: mirror resting in upper position. when pressing the release button, mirror went down quick, then up an err20.

I suspected that the phase sensor gives a non real position. I disassembled the mirror gear.

WP_20151117_22_20_14_Pro WP_20151117_22_20_37_Pro 


On he flex cable the sectors give the position through a metallic brush. I observed some dirt between two sectors. I checked with a multimeter, in resistance mode (NOT continuity).

Instead of the normal infinite resistance, I have measured this:


Ouuuups. This could be the problem. I cleaned it, after that:


This is the normal value. Be careful. As the phase sensor goes into a comparator, should not be a real short. Even a 1-2 kiloohm can be interpreted by the processióor, as a high or low level signal, as this contacts are connected to a voltage divider.

I assembled the camera – and it’s perfect.

The camera has been checked in another service too: they wanted to change the  whole mirror box…


About canonrepair

Ruzsa János. Amatőr fotós, Canon DSLR váz. Amateur photographer. Canon DSLR user.
This entry was posted in 60d, Canon camera. Bookmark the permalink.

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