Check and repair of a non-working shutter unit


Canon 40d is renamed for the shutter failures. By my experience there are wo mail possible reasons: the copper wire on the coil is too short, and after a certain time they just break because the moving. This can be repaired by changing them to a coil from practically any other similar shutter, from 10D to 50D.
The second is, that a small rubber shock-attenuator of the curtains end point (a bumper)  breaks. This also can be replaced.

But let we see, how to check functionally a shutter coil, not only the resistance, but their working.

They get supply through a final stage, and hold the curtain when the motor sets loose the cam in the shutter.

Let we measure this current. As a voltage source I used a LiPo battery, which fully charges has 4,2 volts on the terminals.

(You can disassemble some excellent lithium batteries from the old, but ORIGINAL notebook batteries. Normally the have quality cells, and case on cell is little bit different, the electronic will reject it – but you can use them for long time using one-cell chargers. But be carefull: they have NO PROTECTION – case you make a short, they can explode)   




When this current flows through the coils, they have to held the armed curtains.

When not – just find the broken wire!


About canonrepair

Ruzsa János. Amatőr fotós, Canon DSLR váz. Amateur photographer. Canon DSLR user.
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