3861 movement broken? *Update: Read First Post*

R richard371

So picked up a new 3861 on Friday. I thought I had fully wound it sat am but maybe not. Sunday about noon I went to start the choreograph and the entire watch stopped immediatly. I stopped and started it again and let it sit on the table with the chronograph running and it completely died 5 hours later so I left it. Went to bed thinking maybe this was a power reserve issue. I reset the chronograph and started it about an hour ago and it's still running. I have not wound the watch at all and want to see how much longer it will run. Is it possible its just low on power and thats what's causing this or do I have a dud? Is it normal for a speedy to act this way with the chronograph when the power reserve is low?

R richard371

I would assume a chronograph would work perfectly until the power reserve gets very low then at that point it may run only a few more mins. The power reserve is getting low on mine and with the chronograph running the watch stops more frequently as it gets lower. The watch still runs even after this started 7-8 hours ago. I think it's getting close to dying now as its stopping more frequently.

Im going to do a full wind soon and keep an eye on it. Im just concerned if when the power reserve gets down to 10-15% left should the chronograph have this issue? I thought power reserves are consistent until it's almost dead. I.E. if im getting the full 60 hours is it possible the drag on the chronograph would causes issues like this when it has about 8-10 hours left hours left? I just want to make sure I have an issue before I try to exchange/return it.

Archer

Read it again...he stopped and started the chronograph, and it stopped with the chronograph on. Then when the chronograph was switched off, the watch started running again, which is exactly how I would expect it to act.

Archer

I'll start by just saying there's still doubt that this was actually fully wound based on your post above, so I am assuming it wasn't, because this is your first manual wind, and there are countless threads with people asking how to tell if the watch is fully wound or not. This is why I suggested making sure it was fully wound and then doing the test again. This really needs to be done in order to give you any kind of solid answer, and anything before doing that is just speculation. I know on WUS people are telling you to immediately return it, but in my view there's not been confirmation that there is even an issue yet.

Now onto a more theoretical discussion...



I'm not really sure what "getting worse and worse" means here, but let me explain how this system works, because the questions being asked indicate that some are thinking of this in the wrong way.

People tend to think of the power in a watch like fuel in the tank in your car. The harder you drive the car, the greater the fuel consumption is, so the "faster" it runs out of reserve. This is false.

The power reserve of the watch is a built into the design of the watch, and is a simple calculation based on the length of the mainspring, number of turns of the mainspring barrel, and the ratio of gearing. The power reserve is designed into the watch from the start, and does not change based on running the chronograph or not.

In a watch the mainspring puts out a certain level of torque as it winds down, and that torque will drop off as the end of the reserve is close, and that is one side of the energy equation. The other side is the load on the movement, so think of the watch running when the chronograph is stopped, the load is just what is required to make the watch tick and drive the constant second, hour, and minute hands. When the chronograph is started, that adds the load of all the chronograph parts to the watch, but the spring still only delivers the same torque.

There is a point that is reached when the watch runs long enough, that the torque being delivered by the spring drops off to a point where it can no longer keep the watch running, even though there is still wind left in the mainspring. The point will vary depending on the load side of the equation, so if the watch is running with the chronograph on, then the point at which it stops will happen sooner than with the chronograph off. So if you wind the watch and let it run down with the chronograph running, it will stop, but as soon as you turn the chronograph off, the extra load is removed, and this is enough to get it running again.

So if any of you want to prove this, fully wind your chronograph, set the time, and lay it dial up and let it run down. Note how long it runs and this is test 1.

For test 2, repeat the same thing but this time turn the chronograph on, let it run down until it stops, and note how long it runs. Then turn the chronograph off, which will start the watch ticking, and without winding it again, let it run down and note how many hours it runs. Add the time with the chronograph on to the chronograph off in this test, and it should equal the time it ran for the whole time the chronograph was off in test 1.

This will be true no matter if the chronograph is an 1861 or 3861.

There have been many previous threads on this, so if you search I think some people did this test and posted their results. This was before the 3861, so I don't know how many hours would be "normal" for the 3861 to run once it has run down enough to stop with the chronograph on, and then you switch it off. I do recall people talking about 4 or maybe 6 hours more run time on an 1861.

Hope this helps.