What is at fault ? IWC cal.8541B problem

Hello,

I have been wearing my IWC R810AD with a cal.8541B, the latest iteration of the first pellaton caliber with quick set date set by going 15 minutes back and forth during 23:45-24:00h and hacking function.

I have noticed that it was losing 30 minutes or so when I pick it up in the morning.
On the timegrapher, no alarming signs : amplitude around 250, beat error below 1ms, rate is ok.

The I took an accelerated video and here it is : https://streamable.com/jva9sr

I found more precision about the issue : it only happens during the date changing phase.
This movement has the date by changing 23:45-24:00h. So I figured that it has to do with the date changing.

What parts could be at fault ? 😕

Thank you

Looks like the cannon pinion is loose.

As the second hand keeps turning, the train is running but, the cannon pinion that is a light interference on the centre wheel (which is turning as it is part of the train) is slipping when the date tries to change because there is more resistance when the date is changing. I've not opened one of these but it looks a conventional design and this is the usual issue. You need to take it to a watchmaker and they can tighten the cannon pinion as part of a service.

Cheers, Chris

Thank you Chris. Just wanted to know out of curiosity 😉I’ll drop it off at my watchmaker