Benrus Citation Electronic

[HectorLooi]

I just received this non-working Benrus Citation this afternoon. 

I had a hard time getting the caseback off but managed it with the use of my bezel/caseback removal tool.

Initial testing shows that the pcb is shorted. The balance seems to be ok and swings freely. 

I removed the pcb and tested the coils. It appears to have 2 coils and resistance test shows that the coils are ok.

The movement is an ESA 9158. 

Does anyone happen to have a copy of the ESA 9158 service manual. A circuit diagram would be most useful.

TIA

Here is a close up of the circuit. 

There is just 1 component that I can't identify. What is that silvery blob connected across the resistor? Logically, it should be a capacitor but I've never seen anything like that. 

Probably I need the assistance of @LittleWatchShop. What's that mystery component?

[LittleWatchShop]

35 minutes ago, HectorLooi said:

What's that mystery component?

My initial guess is that it is a diode used to snub reverse EMF when the transistor turns off causing the collector voltage to swing beyond the positive voltage of the battery.  Standard practice when driving a coil.

There appears to be some non-factory soldering going on there.

[HectorLooi]

22 minutes ago, LittleWatchShop said:

My initial guess is that it is a diode used to snub reverse EMF when the transistor turns off causing the collector voltage to swing beyond the positive voltage of the battery.  Standard practice when driving a coil.

There appears to be some non-factory soldering going on there.

I did an image search on google and I see similar sub standard soldering work. I really wonder what's going on. 

I also see some models with a blue metal can device.

I guess I need to dissect it out of the epoxy and test it on the bench.

[LittleWatchShop]

4 minutes ago, HectorLooi said:

and test it on the bench

You have access to the terminals of the device, so you can test to see if it is a diode.

Can you point to where the coils are connected?  I cannot see from the images.

The other image you posted makes me think it is a capacitor...so I am leaning that way.

 

[HectorLooi]

36 minutes ago, LittleWatchShop said:

You have access to the terminals of the device, so you can test to see if it is a diode.

Can you point to where the coils are connected?  I cannot see from the images.

The other image you posted makes me think it is a capacitor...so I am leaning that way.

 

I can't figure out the layout of the circuit yet, as the ends of the coils are embedded in epoxy and soldered to terminalswhich have tracks embedded in the green plastic molding. I'll work on it tomorrow and hopefully produce a schematic. 

[JohnR725]

Typically in electric watch repair there are no schematics. That's because typically in watch repair you not repairing at the component level. It's a module or circuit board it's not component repair. This only becomes an issue if you're trying to restore vintage and the manufacture it never anticipated that you would be doing that so as a consequence there are typically no schematics.

Strangely enough there was a discussion of this movement just a little while back

https://www.watchrepairtalk.com/topic/22373-esa-9158-nos-case-for-balance-complete/

then to me your mystery component looks like a tantalum capacitor. Maybe it's a regular electrolytic capacitor but that's not what it looks like to me.

 

[HectorLooi]

4 hours ago, JohnR725 said:

to me your mystery component looks like a tantalum capacitor. Maybe it's a regular electrolytic capacitor but that's not what it looks like to me.

That was my guess too. But I've never seen a "naked" tantalum capacitor. There is no epoxy coating with any numbers or colour code.

[LittleWatchShop]

1 hour ago, HectorLooi said:

That was my guess too. But I've never seen a "naked" tantalum capacitor. There is no epoxy coating with any numbers or colour code.

Well, it can be divined once we see the connections to the coils.

[HectorLooi]

This is what I traced out.

D - drive coil

FB - feedback coil

Does it make sense?

[LittleWatchShop]

5 minutes ago, HectorLooi said:

Does it make sense?

Yes, it makes sense.  The capacitor is a very high value...perhaps 1uF.  It is a short circuit at the oscillating frequency.  The resistor is there to bias the transistor.  Maybe the coil resistance is 5K which without the 2.5M resistor (RGG is 2500000), that would bias the base current at 200u which is probably too high. 

[HectorLooi]

Thanks @LittleWatchShop

I think the tantalum capacitor is shorted. I'll probably need to rebuild the circuit as all the leads are actually factory spot welded. I think you are correct, someone tried to repair by soldering it at a later date.

[LittleWatchShop]

4 minutes ago, HectorLooi said:

Thanks @LittleWatchShop

I think the tantalum capacitor is shorted. I'll probably need to rebuild the circuit as all the leads are actually factory spot welded. I think you are correct, someone tried to repair by soldering it at a later date.

You should be able to find one small enough size.  Alternative would to use a 1206 SMD capacitor...just a little trickier to assemble.

Going the SMD route, I would do this surgury and attachment.  You just cannot let the heat stay long, otherwise the other joints will melt.