Sunwatch Missing Digit

[charger105]

Hi All.
I'm in the process of refurbishing a Sunwatch module, and have managed to get it to function from a 3V battery source. I replaced one of the resistors which had gone open circuit, and it came up straight away.
Unfortunately though, one of the digits and the colon on the display is out. It's the 2nd hour digit (so if it was 11:30, it's displaying '1 30'). Everything else seems to be working well.

Does anyone know wether this is likely to be a display problem, or an IC problem. I'm hoping it's just a display problem, and that I will be able to swap the display out.

Rgds,
Andrew.

[Synchroserious]

It is most likely not an IC problem.This leaves two possibilities.

1. The wire bond leading to the IC has been broken.Follow the traces on the board leading from second solder pad on display.Internally the 4 digits are refered to as W,X,Y,X,yours is missing the X digit.{OOPS I MEANT WXYZ}

2.Besides a cold solder connection there the other possibility is a bad display.

Once you determine the solder connection is good and the wire bond appears connected you can press on the X digit with a pair of tweezers and it may then light up atleast dim.This would further confirm it is a display problem.

[charger105]

Thanks Howard.

When you say the second solder pad, is that counted from the W end of the display ? If so, the wire bond from the IC that eventually connects to this pad looks intact.

I hit this display joint with a soldering iron, but the X digit and the colon is still out.

I should also mention that the display looks to have taken an 'impact' in the region of the colon and the Y digit (gel is actually missing here). However the Y digit works perfectly.

Any tips on safely removing the display ?

One other silly question. Why is the QC outer can electrically connected to the board (wire soldered to the end) ?

Thanks again for your time.
Rgds,
Andrew.

[Synchroserious]

Yes the W digit is the first pad starting at the W digit end.A desoldering Pump can be used to remove solder from display board to PCB.If you hold heat to the area for more than 4-5 seconds you will fry the IC.So caution is needed especialy on the 7 pads nearest the IC which is right underneath the area you are removing solder(we are talking about MK III and MK IV here).Wick can be used on the pads away from the IC.The pumb or bulb can be tricky to use without the help of a friend holding it steady and pressing the button exactly when you tell him to.


All MK III and MK IV have the positive battery wire conected to the outside of QC can.Nothing silly about this question, it prevents any static electricity or worries about not being grounded when working on a Synchronar/Sunwatch.My dad would have a more technical explanation but this is my take on it.Also it seems to keep the Osc running better without failure.I have noticed some units don't always give you a display without the wire attached.

[charger105]

Thank you Howard. Much appreciated.

Some Hughes QCs have 3 legs. I think one leg attaches to the outer casing. Perhaps it's for similar reasons.

Anyway, I'll let you know how I go. It's such a shame to have to do such brutal 'surgery' on this module........it's so close to working !

Rgds,
Andrew.

[Synchroserious]

Your welcome and the same for anyone else that is inquisitive about the watch.Please pardon my error with WXYX instead of WXYZ!!

[charger105]

I've been putting off replacing the display. I find this kind of activity rather stressful........with exposed wire bonds all over the place (IC and display).
Well, today was was now or never day, and you can see the results below:



The old display is here:


It now works perfectly. All I have to do now is replace the 2 broken reed switches, get some new Nicads, put the solar cell back, and then wedge it all back into the case !

A couple of interesting things I noticed:

The X digit has an extra segment lit perpendicularly hanging down from the top segment whenever a lamp is shining on the module. If I shade the module it instantly disappears. If I remove the shade it instantly re-appears. I also used a flash on one of the photos, and this scrambled the module. It seems the IC is photo-sensitive. See below:


Also, the camera has a good enough response to detect the multiplexing of the display. You can see the digits flickering in real-time on the LCD panel of the camera.

Anyway, thanks to Howard for giving advice with this project. Much appreciated.

Rgds,
Andrew.

[Sully008]

Hi Andrew,

I'm digging this one up because I have several boards with displays on them, but I don't know how to remove them from the dead board to test it. Did you just use a soldering iron w/solder wick @ the contacts to the display to remove the solder? The boards seem so delicate that I'm thinking the heat would kill things. Any insight would be greatly appreciated.

TIA,

Mike

[charger105]

Solder wick/braid is what I used. A vacuum sucker can also be used. Don't hold the iron in place for more than a few seconds. PM sent.

Rgds.