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Mysterious part in an old calculator

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  Mysterious part in an old calculator Piotr Piatek <piotr433@pisi.com.pl> - 2016-04-17 17:17 +0200
    Re: Mysterious part in an old calculator Look165 <look165@numericable.fr> - 2016-04-17 19:47 +0200
    Re: Mysterious part in an old calculator "Ian Field" <gangprobing.alien@ntlworld.com> - 2016-04-17 20:09 +0100
    Re: Mysterious part in an old calculator Look165 <look165@numericable.fr> - 2016-04-18 08:49 +0200
    Re: Mysterious part in an old calculator Piotr Piatek <piotr433@pisi.com.pl> - 2016-04-18 14:48 +0200
      Re: Mysterious part in an old calculator legg <legg@nospam.magma.ca> - 2016-04-18 09:22 -0500

#5964 — Mysterious part in an old calculator

Could someone identify the blue part (marked on the board SC81EIA4R7M), 
please?
http://www.pisi.com.pl/piotr433/misc/bluething.jpg

It's used in an old calculator Casio FX-602P, manufactured in year 1984. 
The part is connected across the power supply pins of the static RAM 
chip uPD444G. It could be a capacitor (but other capacitors on the board 
look ordinary and are marked differently), or perhaps a varistor or a 
Zener diode.

Here's the FX-602P circuit diagram drawn by me:
http://www.pisi.com.pl/piotr433/fx602sch.pdf
and a photo of the whole board:
http://mycalcdb.free.fr/galerie/Casio/casio_FX-602P.4.jpg

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#5965

Seems to be a 4.7 Ohms resistor.

Piotr Piatek a écrit :
> Could someone identify the blue part (marked on the board SC81EIA4R7M),
> please?
> http://www.pisi.com.pl/piotr433/misc/bluething.jpg
>
> It's used in an old calculator Casio FX-602P, manufactured in year 1984.
> The part is connected across the power supply pins of the static RAM
> chip uPD444G. It could be a capacitor (but other capacitors on the board
> look ordinary and are marked differently), or perhaps a varistor or a
> Zener diode.
>
> Here's the FX-602P circuit diagram drawn by me:
> http://www.pisi.com.pl/piotr433/fx602sch.pdf
> and a photo of the whole board:
> http://mycalcdb.free.fr/galerie/Casio/casio_FX-602P.4.jpg

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#5966

"Piotr Piatek" <piotr433@pisi.com.pl> wrote in message 
news:dnhnntFfidtU1@mid.individual.net...
> Could someone identify the blue part (marked on the board SC81EIA4R7M), 
> please?
> http://www.pisi.com.pl/piotr433/misc/bluething.jpg
>
> It's used in an old calculator Casio FX-602P, manufactured in year 1984. 
> The part is connected across the power supply pins of the static RAM chip 
> uPD444G. It could be a capacitor (but other capacitors on the board look 
> ordinary and are marked differently), or perhaps a varistor or a Zener 
> diode.

As a totally wild guess, I would've said a polyfuse - but not if its ACROSS 
the supply pins.

Its probably semiconductor based, maybe a clamp protection diode - but they 
usually don't look that different to ordinary ones.

If it is semiconductor - its probably designed to sacrifice itself to save 
the chip. 

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#5967

Everybody should learn how to read a schematic !

This component is in series with the power supply, so it probably is a 
protection resistor (low value).


Piotr Piatek a écrit :
> Could someone identify the blue part (marked on the board SC81EIA4R7M),
> please?
> http://www.pisi.com.pl/piotr433/misc/bluething.jpg
>
> It's used in an old calculator Casio FX-602P, manufactured in year 1984.
> The part is connected across the power supply pins of the static RAM
> chip uPD444G. It could be a capacitor (but other capacitors on the board
> look ordinary and are marked differently), or perhaps a varistor or a
> Zener diode.
>
> Here's the FX-602P circuit diagram drawn by me:
> http://www.pisi.com.pl/piotr433/fx602sch.pdf
> and a photo of the whole board:
> http://mycalcdb.free.fr/galerie/Casio/casio_FX-602P.4.jpg

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#5968

Thanks to all who responded. The device is indeed connected across (i.e. 
in parallel to) the power supply pins, so it cannot likely be a low ohm 
resistor or a fuse. It appears to be a tantalum capacitor. The measured 
capacitance is about 4.75uF. Photo taken after removing excess solder 
with wick:
http://www.pisi.com.pl/piotr433/misc/bluething2.jpg

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#5969

On Mon, 18 Apr 2016 14:48:29 +0200, Piotr Piatek
<piotr433@pisi.com.pl> wrote:

>Thanks to all who responded. The device is indeed connected across (i.e. 
>in parallel to) the power supply pins, so it cannot likely be a low ohm 
>resistor or a fuse. It appears to be a tantalum capacitor. The measured 
>capacitance is about 4.75uF. Photo taken after removing excess solder 
>with wick:
>http://www.pisi.com.pl/piotr433/misc/bluething2.jpg

It occupies the right footprint for an early smd tantalum and has a
suitable part number (odd to see that on silkscreen) but I've never
seen this particular construction. 

The presence of tack-soldered radial tantalums elsewhere in the
assembly made this an unlikely guess...

If guessing was requested, I'd have suggested an early TVS type for
smd applications. Possibly part of an external wallwart protection
scheme. This would have a similar part numbering system and footprint.

RL

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