A 7A28 (and it's owner) needs help!

[croolis]

So, this lovely watch came to me in 'semi working' condition,
it's been at the watchmaker over these last 2 weeks and came back with a bill + still not working.
The problem is the centre sweep does not .. uhmm .. sweep.
It's not totally dead though - it does twitch.
One would imagine the gear train is gummed up, but watchmaker told me otherwise.

Firstly the watch has had a full service, the interior parts work smoothly and are not worn.
Watchmaker says that the stepper motor for the centre seconds works on its own but doesn't
have enough torque to even turn the first gearwheel that touches it.

Watchmaker says the watch needs a new module, my guess is this is made of unobtainium,
unless I can find a 7A28 with a working movement (or maybe a bad coil) but an ugly case.

I've seen some pictures of a 7A28 circuit board and it seems to me the coils are not actually
soldered to the board - is there any chance of a loose connection between coil and board?

I'm stumped and it's a shame to leave such a nice watch non-operational.
Any help or a pointer in the right direction would be very welcome!

[siralan]

This is what the 7A28 looks like with the PCB removed:




so, yes the coils are independent to the PCB.

My opinion is that if the chrono seconds hand is twitching, then the PCB is probably OK, and also the contact between the coil and PCB is probably good.

It is more likely that there is dry oil or other debris interfering with the stator or the gear train.

Try nudging the chrono seconds hand with a cocktail stick when the chrono is running to see if this helps to get it going.

To find out you really need to strip things down





all the way down



it might be worth asking the watchmaker how far down the watch was stripped and inspected.

Spare PCB's have come up for sale on ebay along with spare coils.

[seikola]

Hi

I'd agree with what siralan said about dirt in the gear train as in my experience when they twitch it's generally a clean that's needed but there are also lots of cases with the 7A series where a faulty chrono hand like yours has been caused by the tensioner being nudged out of position, I know its a longshot that your watchmaker missed something so obvious but stranger things have happened.

Best of luck with it, its a nice watch

seikola

[cobrajet25]

Jul 4, 2015 18:41:09 GMT -8 seikola said:

Hi

I'd agree with what siralan said about dirt in the gear train as in my experience when they twitch it's generally a clean that's needed but there are also lots of cases with the 7A series where a faulty chrono hand like yours has been caused by the tensioner being nudged out of position, I know its a longshot that your watchmaker missed something so obvious but stranger things have happened.

Best of luck with it, its a nice watch

seikola

When they 'twitch' then it's usually a matter of getting them either clean enough, or making sure the rotor in question isn't over-oiled.

An over-oiled rotor won't turn properly.

[Mr.Jones]

Before you do any thing else, please show us a good resolution picture of the movement (only remove the caseback). Often, it's the tension spring for the sweep hand that sits not centered on the jewel. 

It's the little "spoon" dead center. If it's putting pressure on one side of the jewel, the center hand won't move (or move erratically). 

Hope it is this simple. 

Best, Jonas 

[seikoholic]

I have never seen a 7A that won't come right back to life with a full & complete cleaning.  If a hand is twitching then there's almost always drag from contamination going on.  If the circuit is good, and the train truly clean, the watch will function.  You absolutely should not need a complete replacement of the movement.  I've brought back movements so bad that not a single function worked. We're talking a watch where someone used incredibly old-school non-synthetic lubricants on it, lubricants that turned to glue in five years.  Every single wheel was glued in place.  My process cleaned all that out, and the watch is running today.

If your guy can't give you the result you are looking for, drop me a line at [e-mail].