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902 flick wrist too sensitive...

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767Geoff

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902 flick wrist too sensitive...

Post21 Mar 2017, 21:51

902 flick wrist too sensitive...

I have restored the case, keyboard and therefore calculator to functionality. The time display was always functional, the contacts on the flex strip under the keyboard needed cleaning and some carbon contact replacement.

The second problem is the flick wrist function (mercury switch?). It is far too sensitive. A truck rolling by the house may cause it to display when it is lying flat off the wrist resulting in depleted batteries. So the questions are:

    remove (revert to manual push only).
    Remove and replace (where to secure a new less sensitive one

Cheers, Geoff
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767Geoff

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Re: 902 flick wrist too sensitive...

Post02 Apr 2017, 05:09

Anyone?

Please :scratch:
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charger105

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Re: 902 flick wrist too sensitive...

Post04 Apr 2017, 04:47

Are the flick switches the same as used in the Executive models ?
If so, I think I've got one somewhere.
Let me know and I'll start digging !
Rgds.
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767Geoff

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Re: 902 flick wrist too sensitive...

Post04 Apr 2017, 19:00

Thanks for the offer, I don't know the answer so I will remove the back and take a picture of the offending circuit.

Is it a mercury switch?

:Prost: Geoff
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charger105

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Re: 902 flick wrist too sensitive...

Post05 Apr 2017, 09:27

Yes, it's a mercury switch.
I found it:
switch.jpg


The mercury drop moves around, and does short the contacts when in the position shown.
Let me know if this is what you need.
Rgds,
Andrew.
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bruce wegmann

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Re: 902 flick wrist too sensitive...

Post05 Apr 2017, 22:30

The mercury switches operate in a closed-open-closed mode. It's the "open" period that determines whether the watch displays the time or not.
The switch must close between 1/10 and 2/10 of a second after it opens, or there is no display. This 100-millisecond window (time-domain- sensitivity, I think it's called) was intended to minimize the number of "false" display demands created by normal movements, and thus conserve battery life.
The commonest problem the switches develop is immobility of the mercury bead (it begins to stick to the iron electrode, making it impossible for the switch to "open", and so disabling the function). Replacement is the only remedy for this. In between is an entire spectrum of functionality, possibly due to slightly varying sizes of the mercury bead (I am guessing that a lighter bead might be somewhat more difficult to "get moving", due to the difference in getting a smaller mass to "break" away from the stickier, gold-plated brass, electrode, but, that's just a guess). Conversely, a heavier bead might be more easily dislodged, creating a "sensitive" switch. Again, replacement would seem to be the only cure here, as well (the much-smaller switches used in some 800 modules...which appear in the 5503 Dress and some Sport watches, are, of course, subject to the same maladies). It it also conceivable that there could be a defect in the part of the circuit that reads the open-to-close time, and interprets any interruption of the closed condition of the switch as a legitimate time demand (I don't see any possible fix for this).
Replacing an Auto-Command switch in a Calculator impresses me as being very much akin to brain surgery; you have to do a let of damage to get to where you need to go, do the fix, and then repair all the damage you just did, on the way out. You have to split the module wide open, and the switch is on the main circuit board, right next to what must be, judging by its' size, the calculator chip itself. Every wire bond on the board (and there are scores of them) is open and unencapsulated, begging to be dislodged or broken. Given the risks of doing additional or even catastrophic damage, I see this exercise as taking a very big gamble for comparatively little gain.
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767Geoff

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Re: 902 flick wrist too sensitive...

Post05 Apr 2017, 23:40

Well, there you have it!

Leave it well enough alone. I HATE working on thes calcs for the reasons you mention.

Thanks for the offer Charger and thanks for the info Bruce.

Question: I do not need the flick option, is there anyway, without removing the module, to disable it and does this allow for the button push to continue to work.

Geoff
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bruce wegmann

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Re: 902 flick wrist too sensitive...

Post06 Apr 2017, 07:38

Short answer...no. As long as the switch is connected, the Auto-Command is potentially functional. BTW (this may have been addressed before),
there is such a thing as a 903 module, which, if you give the watch a second flick while the time is still displaying, gives you a date display; this module is rare (maybe one-in-twenty or so).
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Re: 902 flick wrist too sensitive...

Post23 Nov 2020, 19:25

bruce wegmann wrote: BTW (this may have been addressed before),
there is such a thing as a 903 module, which, if you give the watch a second flick while the time is still displaying, gives you a date display; this module is rare (maybe one-in-twenty or so).


Haven't logged on here in forever and an old thread I know, but Bruce is the one who told me about my 903 module on one of my Calculators. It's cool!
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Re: 902 flick wrist too sensitive...

Post24 Nov 2020, 01:03

Hey how can you identify a 903 module? I have two calcs that I assume are 902

Thanks

Les
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Re: 902 flick wrist too sensitive...

Post24 Nov 2020, 14:51

Flick the wrist once for time and flick again and 903 will show the date
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Re: 902 flick wrist too sensitive...

Post24 Nov 2020, 14:53

My avatar pic is a 902 but I bought a GF that ended up being a 903
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Re: 902 flick wrist too sensitive...

Post24 Nov 2020, 15:25

The one in the pic was from the collector in Spain (eBay led-forever). I’m sure he’s a big member on here but don’t know everyone. Think I paid $1,200 for that one but included a box, manual, card. The gf 903 was a lucky find on eBay for $450 or so. It had a little tarnish on the keyboard but came right off. No box but the matching gold pen. It’s my wearer when I dress up. The SS stays in its case since its mint.

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