Casio TS-100 Repair Log

Story Time

Half a lifetime ago I was at school.  It was the 10th grade and I noticed something unusual about the digital watch the kid sitting next to me in shop class was wearing.  Below the display was an indentation with a round aluminum disc.  Being a total digital watch geek I had to ask him about it.  That's when I learned that the aluminum circle on the face was a temperature sensor.  It has been so long that I honestly cannot remember the particulars but I ended up trading something with him to get that watch.

At some point in my 20's the watch stopped working and I took it apart to try to fix it - what I thought I could accomplish is beyond me.  Predictably I wasn't successful in my attempts to get it working.  Rather than put it back together, I placed all of its pieces into an empty margarine tub and promptly lost track of it for nearly 20 years.

Fast-forward to last week when my wife was clearing out one of our many catchalls (you know when you've spent all day cleaning and you're down to that last pile of miscellaneous crap and you just want it to be over so you just dump it all into a box and stick it somewhere).  She left me a pile of stuff she thought I might want to keep and among it was the partial remains of my TS-100 - basically just the watch module and housing.  Evidently the margarine tub I had placed it in had shattered at some point and its contents were spilled everywhere.  By the time I recognized what I was seeing, my wife had already emptied the dregs at the bottom of the box into a trash bag.  Fortunately it had not been picked up yet so we dumped out and sifted through the contents of the bag to find what we could.  We managed to recover the back, three of the four screws, the battery clasp and the remains of the gasket and the band.    We did not find the last screw or the coil spring for the beep membrane.

Assessment

I can only speculate as to what kind of weathering the watch had been subjected to since I put it away, but the band had hardened and become brittle, the gasket was brittle and had broken in two.  This suggests some seriously extreme temperatures - might have been left in the garage over the course of several summers and winters.

I took a screw from another non-functional Casio watch to replace the one that was lost.  It's still possible to order new screws from Pac-Parts but they're $2.50 apiece.

I had no idea what functional condition the watch was in, so the first thing I needed to do was put in a new battery and see what happened.  CR1620 is not a very common size but fortunately Walgreens does carry them - well they carried one of them and I bought it.

The First Issue - Swollen Zebra Connectors

When I put the battery in the watch, the display showed numbers and appeared to work at first, but when my finger slipped and I had to re-insert the battery the display ended up all garbled.   It's never a good sign when putting the battery in the watch causes the light to come on - it means something is shorted somewhere.

The next step was to dismantle the watch module to see what might be going on.

TS-200 LCD Holder - something has caused the zebra connectors to swell and warp

I don't have a ton of experience with zebra connectors so it may not be terribly significant but I've never seen anything like this.  The zebra connectors which transmit electrical signals from the watch module to the LCD had somehow swollen in place causing them to warp.  I've read about these connectors shrinking with heat, but I don't know what could make them swell up like this.  Temperature, moisture?  It's hard to know.

When I removed them, I found the compression of being inside the slot when they swelled had caused them to expand unevenly and they ended up with a very pronounced curve.   The slot where the connectors are supposed to rest is 20mm wide, but the connectors had each swollen to over 25mm!

Because I knew that these connectors are prone to shrink with heat, I set my hot air workstation to 212 degrees Fahrenheit (its lowest setting) and gently heated the zebra connectors to see if they would shrink.  Not only did they shrink back to what appears to be their normal size, they also straightened out in the process.

In the image below, the top connector is what they both looked like when I first removed them from the watch, the bottom shows what the connector looked like after applying 212 degree heat to it for about 45 seconds. In hindsight I think placing them in boiling water would also bring them back down to size.

Top - a swollen and curved zebra connector as it was when first removed from the watch.  Bottom - a zebra connector heated with hot air and restored to almost normal size and shape.

After heating both of the zebra connectors they reduced in size back down to about 21mm across which I think is probably their original size.  It's a bit of a tight fit getting them back in, but the curving was nowhere near as dramatic as when I first opened the watch, and unlikely to cause any shorts.

When I reassembled the watch and pressed the battery into it, it came to life, but again when I let go of the battery to try re-insert it with the clasp, the display was garbled.  I had to take a moment to pray about what to do next because it seemed like the watch might just straight up be damaged despite the fact that it would randomly seem to work and then not.

It might seem goofy to insert prayer into the middle of a repair log but it's been hard to argue with the results.  I had the thought that even though I had restored the zebra connectors to their original size and shape, I still hadn't cleaned them.  I disassembled the module again and took a Q-tip and alcohol to all of the pads on the module and to both of the zebra connectors, reassembled the whole thing, prayed again, and glory to God the thing worked perfectly when I re-inserted the battery.

I fastened the battery clasp, inserted the module into the casing and here's what I got:

So far so good.

Second Issue - Missing Coil Spring

Now the next item on the agenda was what to do about the missing "coil spring".  For reference the coil spring is a tiny spring that sticks out of the back of the watch module and makes contact with the piezoelectric pad on the watch back creating a circuit that allows the watch to make beep sounds.  The original coil spring had been lost when the parts were scattered.  I figured it had to be a pretty common part - pretty much every digital watch that beeps uses them, but after searching with Google and a phone call to Pac Parts (the official parts supplier for Casio) I could not seem to find these parts anywhere.  I went back to that donor watch that I pulled the missing screw from, but its spring was too shallow to work.

I'm sure that with a little more time and maybe calling around to watch shops I might be able to find a suitable replacement, but it's just a simple conductor - surely I had something on hand that would do the job.  Eventually I decided to just snip off a tiny length of solder - the metal is soft enough that it's easy to cut and will give a little when pressed.  Turned out to work perfectly - now I've got beeps.

The TS-100's missing coil spring replaced by a small strip of .22" diameter un-melted solder.

Third Issue - Inaccurate Temperature

To my recollection, the temperature sensor on this watch was always more of a novelty than an instrument of accuracy, but I do remember it it at least being somewhat close to reality once upon a time.  With everything back together I noticed the temperature reading was way off - registering about 10 degrees above the actual temperature in the room.  That kind of jarred my memory as being the main reason I took it apart in the first place, but I'm 20 years older now and hopefully a little wiser so I figured I might have better success this go around.

There's no setting you can access from the display that will allow you to offset the temperature displayed on the watch.  Calibration requires taking the back off and adjusting the potentiometer (pot) concealed underneath the sticker labeled "DO NOT TURN".

Turning the pot clockwise will increase the displayed temperature, counter-clockwise will decrease it.

Calibrating this watch to the correct temperature can be a tedious process.  Firstly you have to decide whether you want it to display the correct temperature when worn, or when left on display.  Despite the fact that the thermocoupler's primary source of heat is the aluminum pad on the front of the watch, body heat is enough to raise the temperature of the watch about 20 degrees.

Temperature Calibration Instructions

These are the steps I followed to calibrate the temperature to be as accurate as possible while wearing the watch.  (To calibrate it to be accurate when on display, I suspect all you really need to do is set the watch next to a reference thermometer and turn the pot until the displayed temperature matches the reference thermometer.)

Step 1: Remove the watch back and expose the potentiometer.

Step 2: Try to figure out the ratio of turn to temperature change on the watch display.  I recommend looking at the temperature displayed on the watch face then turning the pot 45 degrees and immediately re-checking the temperature.  What's tricky about this is that with the back exposed the air moving back and forth over the sensor as you turn it is also changing the actual temperature being measured. You'll probably need to check this a couple of times to make sure your results are consistent.  When I did this I found that every 5 degrees of turn was roughly 1 degree of Fahrenheit temperature change.  Your mileage may vary.

Step 3: Find a reliable digital thermometer to use as a reference.

Step 4: With the back securely screwed on, put the watch on your wrist and rest your wrist next to the reference thermometer.

Step 5: Wait until the temperature on the watch stops rising in reaction to your body heat.

Step 6: Continue to check the temperature on the watch every minute to ensure that it's still steady.

Step 7: Note the difference in temperature between the watch display and the reference thermometer.

Step 8: Remove the watch back and expose the potentiometer.

Step 9: Turn the potentiometer (clockwise to increase, counter to decrease) according to the temperature difference you recorded in step 7.  For example, if your temperature was 2 degrees Fahrenheit too high and you got the same 5:1 ratio as I did, you'd try to turn it about 10 degrees counter-clockwise.

Step 10: Replace the back and repeat steps 4 through 9 until you get to step 7 and find that the reference thermometer and the watch are showing the same temperature.

Finishing Touches

A New Band

The band for the TS-100 is an unusual size - 17mm wide at the hinge, but amazingly as of the time of this writing, the original genuine Casio resin band is still available to buy on Amazon - just search for TS-100 band.  Unfortunately the band does not come with the matching spring bars to attach the band to the case.  Since it's such an odd size, not may people sell them.  I ended up having to buy an assortment of over 100 spring bars just to get a pair of 17mm ones.

A New Gasket

And finally it would be the icing on the cake if I could somehow replace the gasket that provides water resistance.  Without a good way to measure the circumference of the gasket (the original was swollen too large to fit) I ended up ordering an assortment of gaskets from Esslinger & Co.  I'll update this post if I have any luck finding a gasket and somehow getting it into the weird shape required to seal up the back of this watch.