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Eta 251.626 Service Walkthrough - The High-End Quartz Chronograph

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ETA 251.626 Service Walkthrough


The 251.626 is often found in mid to high-end quartz chronographs on the market today.




It is a fairly complex quartz movement that has 5 motors, 2 with Red Coils, and 3 with Green Coils.




To begin the service we start by removing the 3 Indicator Maintaining Small Plates, and Date Indicator.

A 1.4mm screwdriver is all the is needed for every screw on the movement.




Here's a reference photo of the 3 screws for the Indicator Maintaining Small Plates.




There are no more components to remove from the dial side of the movement.




Once the movement is turned over, remove the 2 screws that hold the Magnetic Screen.

Once the Magnetic Screen is removed all the coils are very exposed, so work around these coils with great care.




Here's a reference photo of the 2 screws for the Magnetic Screen.




Next unscrew the 6 screws holding the Additional Printed Circuit and gently lift it off the movement.

Store the Additional Printed Circuit away separately and safe from the rest of the parts.




Here's a reference photo of the 6 screws for the Additional Printed Circuit.




Next we tackle the 2 trains with the red coils.

Right Side - Minute Counter

Left Side - Hour Counter




The right and left trains contain different size wheels and should be kept separate for ease of assembly.

We shall start with the right side.

Remove the Minute Counter Bridge




Next remove the Gear Train and the Rotor.




Next remove the Coil and Stator.

Store the Coil away separately and safe from the rest of the parts.




Here's a reference photo of the components and their corosponding screws.

Note the 4 spokes on the Minute Counting Wheel.




Remove the Hour Counter Bridge.




Remove the Gear Train and the Rotor.




Remove the Coil and Stator.

Store the Coil away separately and safe from the rest of the parts.




Here's a reference photo of the components.

Note the 3 spokes on the Hour Counting Wheel.




Store these 2 trains in separate sections in your parts tray, and when cleaning store them in sparate parts containers.




Next remove the Chronograph Bridge




Now remove the Chronograph Wheel




Unscrew the Green Coils and remove them.

Store the Coils away separately and safe from the rest of the parts.




Here's a reference photo of the components and their corresponding screws.




Remove the Train Wheel Bridge.




Remove the Wheels of the Train.




This is quite a complex train of wheels.

So to assist you I've cleaned up the rather cluttered schematic supplied by ETA and colour coded each wheel and it's location on the Main Plate.




Here's a reference photo of the top of the wheels, also colour coded to assist you.




And also the underneath of the wheels, also colour coded to assist you.




Remove the Rotors and Stators.




Unscrew the 3 screws that hold the Upper Plate and remove it.




Here's a reference photo of the Upper Plate, Connector, and the corosponding screws.




This now exposes the Electronic Module.




Remove the Stop Lever/Switch




Remove the Cannon Pinion with Driver.




Then remove the Electronic Module.




Pull out the Stem and Sliding Pinion.

Now store the Electronic Module away separately and safe from the rest of the parts.




Remove the Minute Wheel, the Hour Wheel, and Contact Intermediate Wheel.




Before we can remove the Date Indicator Driving Wheel, we need to pull back the Date Jumper.

Gently lift the tab (Yellow Arrow) until it's at plate level and pull it backwards.

This will pull the arm of the Date Jumper back and allow you to remove the wheel.





Here's a reference photo of the wheels.




Lastly we need to remove the keyless work.

Unscrew the Setting Lever Spring and then remove the Setting Lever, Yoke, Driving Wheel, Internediate Setting Wheel No.1, and the Setting Wheel




Here's a reference photo of the Keyless Work.




The movement is now completely disassembled.




I hope you've enjoyed this disassembly walkthrough and found it's given you the information and confidence to tackle this tricky but rewarding quartz movement.

I will post the assembly procedures tomorrow, Lord willing :)



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Lawson, when do you find time to sleep?

I know how long it takes me to put together a walk through and mine have only a fraction of the detail that yours do.

This is yet another excellent publication, many thanks for time and effort that you must put into them.

Your photography and presentation are absolutely of the highest.

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ETA 251.626 Service Walkthrough

Part 2




We begin the assembly with the keyless work.




Fit together the Setting Lever and Setting Lever Jumper.




Then install the Driving Wheel, Intermediate Setting Wheel No.1, and the Setting Wheel




Install the Yoke




Then slide the saddle at the end of the Setting Lever Jumper Arm into the groove in the Intermediate Setting Wheel No.1.

You will have to then lift the Intermediate Setting Wheel No.1 slightly to position the Setting Lever Assembly as shown below.




Then locate the Setting Lever and Jumper onto their respective posts and slots.

Once screwed down engage the position arm of the jumper onto it's post on the Setting Lever.




Next install the Date Indicator Driving Wheel.

Remember that you need to slide back the Date Jumper




Once the Date Jumper is back in position check that the spring arm is once again down in it's correct position.




Install the Contact Intermediate Wheel, the Hour Wheel and then the Minute Wheel.




Replace the Electronic Module, then fit the Sliding Pinion and the Stem.




Install the Cannon Pinion with Driver.




Replace the Stop Lever/Switch.




Then gently place the Upper Plate back on the movement, making sure the Yoke and Setting Lever are positioned correctly, and that you do not disturb any of the other components underneath.




Refit the bank of Stators and Rotors which have the Green Coils.




Now we come to the trickiest part of this service: installing the Main Gear Train.




To assist in the order in which to install the wheels I will give the part numbers, and colour code the text, to match that of the diagram above.

Start with the Third Wheel [210].




Then the Additional Intermediate Wheel [204]




Then the Second Wheel [224]




Then the Intermediate Wheel [203]




Then the Driving Wheel for Second Counter [8059]




Then the Driving Wheel for Chronograph Wheel 60s [8060]




And lastly replace the Counting Wheel for Seconds or Minutes [8027]




Once the train is in place, take some time to tweak the wheels so that are standing up as straight as possible.


Remember that you have 10 pivots to align with their respective jewels, so taking some time to position the wheels and rotors now can save you a LOT of frustration fitting the Train Wheel Bridge.

I would go so far as to take a little break, have a drink, relax your muscles and mind before proceeding to the next step.


Fit the Train Wheel Bridge and align all the pivots to their jewels, and check the free running of all wheels before tightening down only the 2 rear screws.




Install the Chronograph Wheel.




Next fit the Chronograph Bridge and align the 2 pivot points to their jewels.

This has to be done without the ability to manipulate the wheels directly, so make sure you inspect the jewels with high magnification to be sure the pivots are in their holes.

And again, check the free running of the train.




Replace the Connector




Next we will install the small trains for the Counting Wheel, 1/10s and Hour Counters. 

These are the ones with the Red Coils driving them.

Remember that the wheels are specific for each train and should have always been separated ... DO NOT MIX THEM UP.

We shall begin with the right side.


Install the right side Stator and Rotor for the 1/10s Counter.




Next replace the Driving Wheel for Counting 1/10s [8059/1]




Then replace the Counting Wheel, 1/10s [8027/1]

Note this has 4 spokes to the wheel.




Fit the Counting Wheel Bridge, making sure to align the pivots and test the free running before tightening.




We repeat the process for the left side Hour/Minute Counting Train.

Install the right side Stator and Rotor for the Hour/Minute Counter.




Replace the Hour/Minute Counter Driving Wheel [8630/1]




Then replace the Hour/Minute Counting Wheel [8600/1]

Note this has 3 spokes to the wheel.




Fit the Hour/Minute Wheel Bridge, making sure to align the pivots and test the free running before tightening.




Fit the Red Coil to the right side Counting Wheel Assembly and screw down.




Fit the Red Coil to the left side Counting Wheel Assembly and screw down.




At this stage also screw down the 3 Green Coils.




Refit the Additional Printed Circuit.




Replace the Magnetic Screen.




Secure the Battery Clamp.




Then turn over the movement to the dial side.




Fit the Date Indicator.




And secure the Date Indicator with the 3 Indicator Maintaining Small Plates.




Then fit the dial and hands and test all the functions of the movement.



The service is complete.




As always, I hope this walkthrough was informative and instructive, and gives you the confidence to complete this service on your ETA 251.626



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Brilliant guide with great pictures and instructions. It might encourage me to have ago at solving a problem that seems to have defeated everyone I have asked so far. Perhaps some of you knowledgeable people can advise what is the problem cause.

My Tissot PR200 had it's  ETA 251.262 movement replaced and all seemed to work ok on initial checking but I did not have time to check all functions carefully.

It sat undisturbed for a couple of weeks and then I checked it more carefully.  I noticed then that the Minute register did not reset correctly after a timing event.

I readjusted it to the zero position as per setup instructions. After another timing  event and then zeroing the minute register it did not reset to Zero but to the 5 minute mark.  After further re-zeroing and timing events it did the same thing consistently. 

I checked it some days later and the problem was slightly different in that after re-zeroing and timing event resets the Minute register did not reset correctly and seemed to overshoot the zero reset point by a variable amount of between 3 and 12 seconds.

All the other functions seem ok.

Any ideas most welcome as I have no clue as to what produce these symptoms.  Many thanks

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