Mercury Calculator

[bucko170]

I have a Mercury calculator watch the same as pictured in the link below, when new batteries are installed both the time and calculator functions work without fault and it keeps excellent time, however within 3 - 4 weeks the watch display will freeze with a constant single digit, if I remove and then replace the batteries the watch will reset and work again and the pattern will be repeated.
The fault will appear even if the watch is left undisturbed, could it be a sign that the QC is starting to fail?


http://www.ledwatches.net/photo-pages/c ... n-calc.htm

[rewolf]

Looks like either the QC or the oscillator circuit.
It often helps to solder a resistor in the range of 10..22 MegaOhm parallel with the QC (in case of a weak oscillator).

[bucko170]

Looks like either the QC or the oscillator circuit.
It often helps to solder a resistor in the range of 10..22 MegaOhm parallel with the QC (in case of a weak oscillator).

Yikes sounds scary.

I had another thought, could it be because I installed alkaline batteries and a dip in voltage causes the fault - the newer the batteries the better\longer it seems to last?

[bucko170]

The same fault has just occured after using the calculator function, could it be possible that I am leaving the watch in the calculator mode and sending it beserk?

Does anyone have any instructions for the watch?

[retroleds]

Mick:
If your calc. has the snap on back, be sure to clean the back very well, and (suggested), rub it with a little electrical contact cleaner to keep the metal from oxidizing. Some have battery clips to make the connection better, others just use the bare back for all. Making and breaking contact rapidly can cause any watch to "Freeze"....it could be shifting about when buttons are being pushed.

The spring clips for the buttons - frequently installed wrong and can cause a short. There are three contacts on both sides of the module - if the middle one is contacted it can cause the malfunction you are describing. The clips are made to slip onto the plastic lip of the front of the module, so they can be slipped in along with it. The funny thing with them(clips) - they don't touch the contacts on the module themselves, they miss reaching the contacts by maybe 1 mm. The buttons make the actual contact to contact connection, yet the spring clip is JUST barely caught by the larger lip of the buttons for the spring action. The lip/head on the inside end of the buttons keeps them from falling out of the case. Fortuitously, I just set up one of these for a sale, so I have the parts out and will include a few photos now.

And if pulling the module, pull the upper end of the spring clip in toward the module, to get it to unclip from it's notch on the side of the case - just get one side up a few mm., and then do the other and pull straight out by the plastic between the batteries.

BTW: If you want to replace that crystal, I have a handful of the two lead ones, salvaged from defective Hughes Dual modules(bad displays but kept good time)...that is not your standard speed quartz crystal.

I should be working on other things, but it is oppressively hot here, so it is good to hide inside. 93.6 F or 34.2 cel.

[bucko170]

Thanks Ed, I will investigate further, thank you for the advice and photographs.

BTW I have just lost a segment on my Pulsar calculator - any hope for that?

[azimuth_pl]

silver epoxy - the wires are exposed:


as for the Hughes you might clean all possible contact plates, however the quartz is usually the issue:

[LEDluvr]

Facinating. (insert Spock emoticon here)

[bucko170]

Superb pictures....... although it's very scary seeing all the things that I could potentially break, snap or general mess up

Best leave the fine tuning to the experts me thinks

[bucko170]

I finally got around to having a look at the watch, here are some photographs of what I found when I opened the watch up.

1. Photograph of the back case, the screws are different so I suspect the watch has been tampered with previously.



2. Back case removed.



3. Close up photograph of the internal contact.



4. Photograph of the parts.



The spring clips are missing are the contact strips correct? - I suspect not.

[azimuth_pl]

your watch is all ok,
the spring clips holding the module together do not appear in every piece. I have two of these and neither had them from the beginning.

contact strips?
the spring clips for the buttons are there so the watch is all complete.
the battery screws on the back do not have any springs so the contact with the batteries is not perfect. add some aluminium foil on top of every battery to secure 100% contact.

[bucko170]

Thanks Piotr.

When I put the watch back together and pressed the command for the time display it showed a single digit (number 1) across the display one was very bright the rest very faint, when I pressed the command for the date I got the same thing only difference was it was number 2 displayed and not number 1.

I have had similar show on previous battery changes and the fault cleared up when the watch was left, so I have left it with the batteries in and I will retest it tomorrow. However I am not that confident the fault will clear this time as previously the watch did attempt to show the time along with the 'ghost' digits.

I took care when dismantling the watch but being an amateur I can't rule out the possibility that I have disturbed something whilst taking it apart, although the watch has not been tried with batteries for a few months and the fault has been present for quite a while and so it may just be a coincidence that it choose to stop working now.

I will test it and try the aluminum foil on top of each of the batteries and see what happens.

If the QC is faulty should the calculator part of the watch still work, or would a faulty QC scramble the entire watch?

[azimuth_pl]

hard to say... but from a logic point of view, the calculator should work with a busted quartz.
one of my watches shows very similar symptoms.
I tried a new quartz, cleaned everything, checked the chips under a microscope....no signs of damage, leakage.
I guess some of these might just show signs of aging and have a mind of their own.

ps. when assembling the watch from total demolition make sure that there is contact in all places (the traces/tracks are thin)

[bucko170]

Just an update on the watch.

The fault is still present as described.

The calculator does function correctly.

I am going to double check that I had reassembled it correctly.

Any thoughts/comments/suggestions etc .......

[azimuth_pl]

no more ideas