1976 Bulova quartz watches. New project? Waste of time? Let's find out

[ManSkirtBrew]

While my heart lies with mechanical watches, I'm a sucker for a pretty face, and these were too nifty to pass up.

Neither appears to work, but I haven't dug in yet, or even found the correct batteries yet (Varta 548 or Renata 386).

I took it apart and found what appears to be a ceramic circuit board with SMD components on it. Let the research begin.

[rehajm]

Red LEDs? that’ll be nice if you can get them working…

[ManSkirtBrew]

Reddit just delivered on this, which is a good start.

 

Well, I just took a closer look, and it appears the board is cracked in a couple of places. Doing some continuity testing, it appears all of the digit traces that go to the transistors are broken

This one between a transistor and display seems bad as well.

I grabbed the other guy, and all of the traces are connected as far as I can tell. Hopefully tomorrow I've got some new test leads coming in, so I'll power up the board with my variable power supply and see what happens.

[nevenbekriev]

The broken PCB is not a problem, but this is if the display is not broken too. The usage of the word 'digital' for the traces is making me smile, this is just traces and they do not have idea what kind of signals will they conduct... You can use thinn enameled wires to reconnect the leads of the parts. I am a little frightened when read that You intend to use regulated power supply. This is the normal way, but one has to know what He is doeing.

[ManSkirtBrew]

9 hours ago, nevenbekriev said:

The usage of the word 'digital' for the traces is making me smile,

If you take another look, I typed "digit," as in the traces that select the digits. Pins D1, D2, D3, and D4 from the Mostek chip. Sorry that I wasn't clear, but I'm glad I made you smile.

Yes, using enameled wires to reconnect the leads is exactly what I intend to do, provided the display is working. I'm starting with the one that doesn't have a broken circuit board to take one variable out of the testing process.

9 hours ago, nevenbekriev said:

I am a little frightened when read that You intend to use regulated power supply

Have no fear. I am familiar with how to use my power supply.

Edited April 4 by ManSkirtBrew

[eccentric59]

6 minutes ago, ManSkirtBrew said:

I am familiar with how to use my power supply.

Isn't that what Dr. Frankenstein said right before ....

 

[ManSkirtBrew]

Just now, eccentric59 said:

Isn't that what Dr. Frankenstein said right before ....

 

I know; I'm famous for famous last words

[eccentric59]

Edison said "Genius is 1% inspiration and 99% blowing things up." Or something like that.

 

[ManSkirtBrew]

Testing continues. I de-soldered the main chip from the broken board to find out where the vias underneath it go:

And then I took a closeup picture of what I assumed is a trim pot, but when I measure the resistance across it the value slowly rises as if it were capacitive. So I'm hoping someone here can tell me what we're working with.

Then I figured I should test out the LED display, so I applied voltage to it, with kind of weird results.

I had the ground attached to the battery -, and +3.1v attached to my tweezers. It was pretty neat to see it light up!

Edit to note I think the weird results are because the inputs of the transistors are floating, although I'd expect no result at all in that case.

Also edit to include the schematic I put together.

Edited April 6 by ManSkirtBrew

[JohnR725]

looking at this brings up memories? At one time these newfangled LED watches were newfangled and there was way more of information. Tech sheets soldering stuff. There is even a kit with super tiny gold wire to reattach the wires to the LEDs because some of them were not covered with epoxy. Then yes it did come with the conductive glue you definitely need a microscope for this one. So you've missed out on all the fun stuff from the old days and now have to reinvent the wheel.

Usually the variable thing is the variable capacitor to regulate the frequency of the watch.

Oh and yes there were available separately in case you broke yours or something one to replace its.

as you like playing with your soldering iron vintage at the first link modern or something similar at the second link

http://rk.nvg.ntnu.no/sinclair/other/blackwatch.htm

https://www.makershed.com/products/solder-time-watch-kit

 

[ManSkirtBrew]

4 hours ago, JohnR725 said:

now have to reinvent the wheel.

It's funny you say that--I'm already considering turning this circuit diagram into a manufactured PCB. I just have to figure out the mystery square.

4 hours ago, JohnR725 said:

http://rk.nvg.ntnu.no/sinclair/other/blackwatch.htm

This is a great read, thank you!

[JohnR725]

for power supply this thing draws a lot of current why do you try a car battery will give you lots of power make sure you fill it for us please.

Now joking aside you want to pay attention because typically the two batteries are in series student need 3 V. Then when all the LEDs are on it does draw a little more power than a regular quartz watch. Then yes this is bringing up memories of the old days as yes they had power supplies for the use.

What is interesting is is just how fast knowledge of this period of watches seemed still disappeared were the knowledge of how to work on them etc. although let's see what searching the Internet brings up for you. One of things this article handset is yes all the semi conductor companies got into integrated circuits for digital watches plus a lot of the US integrated circuit manufacturers even got in the manufacturing digital watches. Then as nice as the article is it doesn't cover all the watch repair test equipment etc. Then by the way this was the years of crisis for the watchmakers as these newfangled watches don't seem to have any gears in them and where's the balance wheel? Yes the watchmakers panicked again like they like to do with new tech which is some point in time fades away in mechanical watches are popular again.

https://www.hodinkee.com/articles/four-revolutions-led-watches

looks like the digital watch isn't gone after all?

https://www.hamiltonwatch.com/psr

then yes I know it's not your watch but you might find the reading interesting especially when you get towards the bottom as to how he fix the pesky watch doesn't work problem. Then yes a heck of a lot of these watches failed and in the old days people didn't like failed digital electric watches and rather than throwing them away which a lot of dead a lot of them were given away?

http://pulsarledtime.com/Blog-Article-on-PLT-1-Module.html

 

 

 

 

 

[nevenbekriev]

4 hours ago, ManSkirtBrew said:

...I'm already considering turning this circuit diagram into a manufactured PCB. I just have to figure out the mystery square.

Do You consider Youself capable to produce PCB? I mean, You thought the adjustable element is resistor, and now I see that You don't know what is the 'mistery' square. And it is the quartz crystal...

Further more, what You did in the video is absolutelly out of healthy reason, and IF the chip that You touched with the tweezers (conected with the Vcc) is still working, it will be only because there are current limiting rezistors inside for the display segments driving outputs. I hope You didn't touch another legs but only segment drivers...

Do You know what is dynamic indication? This is the type used in this watches. My advce is to find and read some information on how it works, then to understand what type (common anode, common cathode) display is it and how exactly the display driver drives the display. Untill You understand everything well enough, it is highly not recommended to make experiments, especially if they include using power supply.

 

[ManSkirtBrew]

48 minutes ago, nevenbekriev said:

You don't know what is the 'mistery' square. And it is the quartz crystal...

Thank you for your kind advice. So you're telling me this is the quartz crystal:

And not this:

 

That's so strange. I thought the first one is a capacitor (after further testing) and the second one is the quartz crystal.

But I'm here to learn, so thank you for your input. I will put the project away until I learn everything I need to know to continue.

[nevenbekriev]

Sorry, this is a (small, 3-5 pF) capacitor and it is in paralel to the quartz crystal. And the quartz is on You second photo. I just traced to where it is connected and it is connected on the place where the quartz must be connected, and sometimes quartz crystals have strange look. I didn't have the image of the other PCB side, where the crystal is seen

[JohnR725]

51 minutes ago, ManSkirtBrew said:

That's so strange. I thought the first one is a capacitor (after further testing) and the second one is the quartz crystal.

the thing that looks like a crystal and functions like a crystal is there to confuse you. Is to confuse you into thinking it's a crystal because that's what it actually is. Then the other thing it looks like it has four leads? but sometimes on surfacemount components you can have four leads for component that might only need two leads.

 

 

 

[ManSkirtBrew]

1 minute ago, JohnR725 said:

but sometimes on surfacemount components you can have four leads for component that might only need two leads.

I did realize later it only has two leads, top and bottom.