Compu Chron Calculator - how easy to fix a dead segment?

[spinchb]

Hi All,

I've acquired a Compu Chron Calculator watch. It was sold to me as broken, but luckily I'm quite persistent and I've upgraded it to completely functional minus one segment...bottom left of the hour digit! In a watch with so many digits why does it have to be the hours digit! So 5 and 6 o'clock are the same time.

I haven't ripped it apart yet, as it's mint in every other way. I don't want to wreck anything unnecessarily. My question is...Is it possible to fix a broken segment in one of these? Could it be something simple, bad solder joint? Or, likely something trickier? Broken wire bond? Before I commit to pulling it apart and looking for myself, I thought I should get an informed opinion from you all.

Thanks!

Best,
Shawn

https://www.dropbox.com/s/yoexr8o941kby0b/CompuChron-Calc.jpg
https://www.dropbox.com/s/xza3r0p55g16pvi/CompuChron-Calc-digits.jpg

[767Geoff]

I vote wire bond.

If easy access and you are good with silver epoxy and you have a steady hand and you don't sneeze and there is no earth quake then yes you can.

Seriously a steady hand and a wire bond that is present then yes, silver epoxy. I haven't looked at one of these so I don't know how exposed the bonds are.

Hanno does wire bond repairs, still waiting for my 901 and 902. But they are done.

Geoff

[spinchb]

Thanks Geoff,

I agree, it's probably a wire bond. Anyone know if the bonds are accessible, has anyone here successfully repaired a display on one of these?

Cheers,
Shawn

[azimuth_pl]

the loose-wirebond display is secured with a plexi cover applied with glue:
http://www.crazywatches.pl/compuchron-h ... r-led-1976

[spinchb]

Thanks for the link! I get it now. Usual Hughes with the plastic covering over the bonds. The display could be swapped out with a donor watch. These "Battlestars" seem to go for $150 - $200 broken, so a donor watch is a bit dear in price. I'm trying to source someone who does wire bonds in my part of Canada. It should be pretty simple for someone with the gear and experience.

Cheers,
Shawn

[azimuth_pl]

if you only have a few bonds broken you can do it yourself with a 10x magnifying glass and a stead hand.
use silver epoxy or wire glue which is super conductive. available on the bay

[spinchb]

What's the difference between working with Wire Glue and Silver Epoxy? Is there an advantage of one over the other in this sort of application? I actually didn't know about Wire Glue until now. It's a lot cheaper for sure. Seems pretty cool. I can imagine a 100 and 1 uses.

S.

[azimuth_pl]

silver epoxy comes in many forms and finding one that is super conductive might take a while and be expensive....the more silver the higher the price.
wire glue seems to be a newer invention based on graphite and the only downfall is that it is black so might be more visible on displays and visible parts of circuitry.

[bruce wegmann]

The problem with graphite is, it's the same stuff used in carbon resistors, and is far less conductive than silver (in fact, at room temperature, nothing is more conductive than silver, even copper). I would never use a carbon-containing material to repair a wire bond...higher resistance means less current will get through the connection, so, you might get your segment back, but it will be slightly dimmer because it's not getting enough power. Do it right and use the silver epoxy; the best stuff is made by MG Chemicals. It has ultra-fine silver particles produced by precipitation out of solution; gives the most uniform distribution of silver grains and the lowest-possible-resistance connection. A single successful repair pays for the kit, and there is enough to do more than a hundred (14 grams). There is nothing useful to be gained by cutting corners here. BTW, I wouldn't recommend trying to do wire-bond repair at only 10X magnification. I have a B&L StereoZoom microscope here, and my experience suggests that at least 40X, and preferably 60X, is needed to get a clean, reliable repair. Bonding pads are really tiny, on the order of .006 inch (0.15mm) square (some are even smaller), so there's no room at all for sloppiness (you might end up complicating your problems, perhaps beyond the point of solution). Finally, you need an appropriate method of applying these vanishingly-tiny specks of adhesive. Ordinary pins and needles are about as useful as railroad spikes in this situation, and I have found only one good alternative...what are called "biological probe needles". These things are solid tungsten, diamond-ground to a taper and a point with a radius no greater than .0001 inch (.0025mm, or 2.5 microns); at 60x, a pin looks as dull and rounded as a baseball bat...the probe needle still comes to a virtually dimensionless point (you actually have to be careful handling these; touch them to your skin under any pressure, and they sink, virtually without resistance or pain, into deeper tissues...they are much sharper than acupuncture needles!). This is a case a bit like brain surgery; you need the right tools for the job, and improvisations usually end up badly.

[azimuth_pl]

Bruce, all very useful but people asking most of the questions on forums are far from being experts without special equipment. We can share scientific methods for newbies but I find it better to give easy to use practical ways of getting a job done. You say that you'd not recommend wire-glue....if you don't have anything else (or you can't afford silver) then it's better than nothing as long as it doesn't cause any harm. Also 10x magnification works perfectly, can't help it that others need 40-60x

[bruce wegmann]

You're forgetting that I've been doing this stuff for a long time (over ten years, now; nobody starts out as an expert, but you can minimize the failure rate by at least starting out with the right tools for the job), so I've already been through the worst of the trial-and-error stage. I'm just trying to steer this Member to methods that have the HIGHEST PROBABILITY OF SUCCESS, not the cheapest ones. And, since the whole point of this exercise is to return a watch to fully functioning condition, I think I've done my level best to do just that (and fixing broken wire bonds is the most challenging repair there is). Seriously, if I couldn't afford to spend twenty or thirty dollars to fix a $500 watch, I'd hold off any impulse to do a quick-and-dirty job of it until I could; there is too little to be gained, and potentially too much to lose, to justify the risk. Let's not step over dollars to pick up pennies...

[azimuth_pl]

All correct Bruce, your hints are worth every penny.
However many LED enthusiasts have either spent their last dollar on their single treasure (hoping that it works) or they got a bargain and still try to get an affordable fix.
We simply need to have a wider perspective and give people a few options starting with the easier ones. Trial and error is also an important step on the learning curve.

[bruce wegmann]

Sure it is, but NOT on $500 watches. Get the screw-ups out of your system on $30 Fairchidls and the like. And i guess I'm just not much of a gambler...I've lost count of how many time I've advised people NOT to buy something "hoping that it works"; that's a great way to have NO money available when the real good deal comes along (especially, if you're not experienced at repairs). I think there's a practical limit to how wide a perspective can be and still be useful; I'm all for an open mind, but not so open the wind whistles through it...

[spinchb]

Thank you for the wise comments gentlemen! I will push forward with knowledge and wisdom. I think I probably need to buy both and experiment on some non-critical tinkering to see what's what. I do other electronics work in addition to watches, so I have a few ideas for both compounds. I won't be touching this Compu Chron until I know what I'm doing, or I find an experienced person to do it for me. It's certainly not worth it to screw up a nice watch. I'm feeling rather attached to it already.

Cheers,
S.