Bulova Accutron Quartz TZ

[HectorLooi]

I just got this non-working Bulova Quartz this week.

It houses a Bulova 2426.10 movement. When power was applied, the motor just twitches. My Bulova meter showed that the pcb appears to be functioning. A resistance check of the motor was around 640 ohms. When 1.5V was applied directly across the motor contacts, the rotor only twitches. This is something that another member, @PastorChris, experienced a couple of months earlier.

I decided to cut open the motor to investigate. The pivot of the pinion was so brittle that it snapped off the moment I pulled on it.

The spot weld of the top cover was so weak that my razor blade cut through it with one tap and went straight into the coils, thus cutting it. 

The lower cover took a bit of bashing to remove it. I discovered a couple of metal filings across the leaves of the magnet. That was probably shorting out the magnetic field and the cause of the twitching.

This is a really brilliant design but probably very expensive to produce. I'll be on the lookout for another similar movement. 

[HectorLooi]

I had a closer look at the stepper motor and I just can't figure out how it is propelled in one direction. In a normal quartz clock, the Lavet motor has portions of the iron core stator cut away to upset the magnetic field when the coil current is off, to rotate the rotor a little bit more. And when the next pulse to the coil comes on, it pulls it to the next stable position.

But in this motor, I just can't figure out how the rotor can move in one direction. If a simple alternating pulse is used, the motor will simple twitch. And that was what it was doing.

Could it be that the drive pulse in a Bulova is not a simple single shot square wave? So I pose this question to our Prof @LittleWatchShop. Does the Bulova motor use a simple bipolar square wave drive pulse?

[JohnR725]

On 9/29/2022 at 7:41 PM, HectorLooi said:

Does the Bulova motor use a simple bipolar square wave drive pulse?

is a little bit cryptic in the service manual because it's exactly in the middle of the page where half the paragraphs on one side and half is on the other.. It indicates that by alternating the contacts on the motor the same as you would any other stepping motor  it's supposed to step.

The problem with these sealed motors are there not really meant to be serviced.. It's a design not unique to Bulova I know there were some other companies that had sealed motors that looks similar.  They just didn't anticipate that we would be wanting the watch to run all these years later they were met the last forever.  Like for instance if you look at the bearings white color  I'm not even sure that's a sapphire I think it may be nylon. Or maybe Teflon.

 

992369810_Bulova242.pdf

[Michaeluk]

On 9/30/2022 at 3:41 AM, HectorLooi said:

I had a closer look at the stepper motor and I just can't figure out how it is propelled in one direction. In a normal quartz clock, the Lavet motor has portions of the iron core stator cut away to upset the magnetic field when the coil current is off, to rotate the rotor a little bit more. And when the next pulse to the coil comes on, it pulls it to the next stable position.

But in this motor, I just can't figure out how the rotor can move in one direction. If a simple alternating pulse is used, the motor will simple twitch. And that was what it was doing.

Could it be that the drive pulse in a Bulova is not a simple single shot square wave? So I pose this question to our Prof @LittleWatchShop. Does the Bulova motor use a simple bipolar square wave drive pulse?

Hello

I have the same problem, I took the step motor off and demagnetised it while moving it in a circular motion and got about 5 ticks of the second hand before twitching again.

I noticed the step motor twitches back and forth when the second hands were moving if that helps.

Im tempted to open it up, how hard is it getting that lower cover off, does it pry off or did you have to cut it?

 

 

 

[HectorLooi]

1 hour ago, Michaeluk said:

Im tempted to open it up, how hard is it getting that lower cover off, does it pry off or did you have to cut it?

It took quite a bit of brute force. As you can see, the pinion broke off. I wouldn't recommend opening it.

[JohnR725]

I have a diagram of a similar stepping motor. You'll notice that the rotor is a magnet and

10 hours ago, Michaeluk said:

I took the step motor off and demagnetised

That's an interesting word quoted above demagnetised The stepping motor the same stepping motor that has a magnet?

Then of very long time ago I used to work in a shop where we service these. There are doing warranty work for a company that gave away as a 30 year watch. We took the plastic off the bottom and I just can't quite remember whether we sprayed them with free on because Freon was available at that time when the works really well for electrical components. Or we might have dipped amend the cleaning machine but make sure the fluid is super super super clean because otherwise you're going to get particles all over the magnet. But I'm actually leaning towards we might a sprayed it with the Freon. I don't know if you get any equivalent electrical cleaning product today you might build do it with isopropyl alcohol perhaps.

[watchweasol]

Carburettor cleaner is fast drying and used for cleaning the jets, if all else fails worth a try, brake and clutch cleaner also as they dry fast and no deposits. 

[Neverenoughwatches]

4 hours ago, watchweasol said:

Carburettor cleaner is fast drying and used for cleaning the jets, if all else fails worth a try, brake and clutch cleaner also as they dry fast and no deposits. 

Electrical contact cleaner spray is available in UK.

[Michaeluk]

On 1/20/2023 at 9:29 AM, JohnR725 said:

I have a diagram of a similar stepping motor. You'll notice that the rotor is a magnet and

That's an interesting word quoted above demagnetised The stepping motor the same stepping motor that has a magnet?

Then of very long time ago I used to work in a shop where we service these. There are doing warranty work for a company that gave away as a 30 year watch. We took the plastic off the bottom and I just can't quite remember whether we sprayed them with free on because Freon was available at that time when the works really well for electrical components. Or we might have dipped amend the cleaning machine but make sure the fluid is super super super clean because otherwise you're going to get particles all over the magnet. But I'm actually leaning towards we might a sprayed it with the Freon. I don't know if you get any equivalent electrical cleaning product today you might build do it with isopropyl alcohol perhaps.

Hello thank you for your reply.

My theory was to demagnetise the magnet temporarily to shift the debris.

Whether thats a flawed theory or not i do not know but it worked.

The 5 ticks i was getting after was actually due to the battery being drained, i accidentally put in the original right sized battery after demagnetizing instead of the brand new slightly wrong sized that i had started with.

Its been running flawless for the past 24 hours.

On 1/20/2023 at 9:29 AM, JohnR725 said:

I have a diagram of a similar stepping motor. You'll notice that the rotor is a magnet and

That's an interesting word quoted above demagnetised The stepping motor the same stepping motor that has a magnet?

Then of very long time ago I used to work in a shop where we service these. There are doing warranty work for a company that gave away as a 30 year watch. We took the plastic off the bottom and I just can't quite remember whether we sprayed them with free on because Freon was available at that time when the works really well for electrical components. Or we might have dipped amend the cleaning machine but make sure the fluid is super super super clean because otherwise you're going to get particles all over the magnet. But I'm actually leaning towards we might a sprayed it with the Freon. I don't know if you get any equivalent electrical cleaning product today you might build do it with isopropyl alcohol perhaps.

Heres a gif of the operating stepper motor for your interest.