Minute counter hand in a chronograph moving two minutes per time

[Stian]

Hi guys,

 

I have an old Landeron 39 for which the minute hand when using the chronograph function moves two minutes instead of one minute per interval. The hand starts moving slowly the instant the minute starts, and then quickly slides another minute when the minute finishes. This then happens for every minute.

 

Any idea what this can be without opening the watch?

 

Thanks,

Stian

 

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[Delgetti]

Hm, I'm not familiar with the Landeron 39 movement, but could this be a problem with the adjustment of the sliding gear?

 

Here is a quote from a post from @GuiBer which describes the area on a landeron 248:

"Particularly tricky was tuning the depthing  between the sliding gear teeth and the dart tooth on the seconds wheel chronograph runner. If there is too much depth the minute runner will jump two minutes at a time, and with too little it will not jump!

The cam (eccentric stud) to adjust is this one :

 

[Geo]

I think it will probably be a problem with the minute jumper spring.  Either slightly distorted from earlier work or not adjusted properly.

Here's what the jumper looks like.

 

[RyMoeller]

39 minutes ago, Delgetti said:

Hm, I'm not familiar with the Landeron 39 movement, but could this be a problem with the adjustment of the sliding gear?

Here is a quote from a post from @GuiBer which describes the area on a landeron 248:

"Particularly tricky was tuning the depthing  between the sliding gear teeth and the dart tooth on the seconds wheel chronograph runner. If there is too much depth the minute runner will jump two minutes at a time, and with too little it will not jump!

I second this assessment.  The sliding gear, which is sometimes called the intermediate wheel, is adjustable via an eccentric.  I've had cases where the depth was too great which results in the dart tooth on the runner grabbing two teeth on the intermediate wheel.

Other possible suspects could be a misaligned dart tooth (on some chronographs it can be adjusted by rotating) or an improperly adjusted minute recording pawl.

[Stian]

Brilliant, guys, thanks!

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