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How to fix AC and Ans Button on fx-9750g plus calculator.

TheuTrich

Nov 17, 2021
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I have a graphics calculator, it still turns on but its circuit board is damaged. The button AC/on and the EXP(Ans) button do not work. is there any way to fix it?

Here is a picture of the circuit board.

back of the board
board1.jpg

front of the board
board0.jpg
 

Harald Kapp

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Nov 17, 2011
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Where's the damage to the circuit board?
Maybe all that is required is cleaning the pcb and the back of the keyboard, then repair the defective layer of contact material on the back of the keypad.
See here and here.
 

Martaine2005

May 12, 2015
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The component side looks like it needs more repairs to broken traces. A few have been previously repaired.
Use a multimeter in continuity mode and check the traces that immediately stand out. Some of the soldering is very poor and the battery contact looks cracked.
I’m actually surprised that ONLY two buttons don’t work.

Martin
 

TheuTrich

Nov 17, 2021
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I'll try to clean it up and fix other traces of damage if something happens, I'll reply. Thank you
I don't know much English.
 

TheuTrich

Nov 17, 2021
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Hi. I tried to fix a few bad traces and it fixed the Ans button (sorry for the mistake it was a '(-)' button, not 'EXP'). The AC/ON button is still unusable so I'm still trying to fix the ac button.
 

Martaine2005

May 12, 2015
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Post a photo of the button layout. Somebody here may be able to see what trace needs fixing.
But I count at least 7 traces that look bad.

Martin
 

73's de Edd

Aug 21, 2015
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Sir TheuTrich . . . . .

Trời ơi‎ . . . . .

First question is what ocean / or / wavefront was this unit subjected to before being hurriedly retrieved ?
BUT . . with it having no immediate or forthcoming followup of a deionized water, heavy scrub down of the board and its drying out ?

Tracking down the AC keypad function . . . .

Photo 1
WHITE
rectangle on cursor button is just being used for referencing the scaling of photos 2 and 3, also the RED asterisks.
Fine RED rectangle mark ups on AC key . . . . is your current PROBLEM.

Photo 2
Yellow
asterisks areas . . . .mostly within the PINK fenced in area . . . . are points where a left handed painter, afflicted by spastic palsy . . . . and a bad case of the hiccups is set free with his # 0 or 1 sable hair brush and a bottle of colloidal suspended graphite touch up conductive paint *** to try to overcoat some of the factory fired / flow-fused via bridges ( those, comparatively being , 3 degrees superior).
*** Confirmed by its distinctive micro glitter surfactal reflections
***This is usually what is used to resurface the mating keys to these contact grid pads.

Photo 3
Where most of our tracing goes on, with sometime back referencing to its flip side on Photo 2.

HERE GOES THE FLOW
. . . . . stand aside !

PART 1 . . . . .FLOW PATH

Start at the RED arrows connection at PAD finger #9 and its foil goes to the right and then up left to encounter the first VIOLET via Notice, that it is used to route around, on the backside, of the 4 foils coming down in the WHITE rectangle.
Just above its right terminal is an exposed copper test terminal. Now is a good time to use ohmmeter to measure to that test point from the finger #9 to see what resistive loss is expected for a factory via resistor jump , and that one is being factory pristine.
Continue down the right direction path until it encounters two diagonal foils in its path, there the BLUE mark up via has to originate backside.
Then the bottom via connection takes a copper foil path to go straight down and into the TOP contact of your AC key contact pad. You have now completed half of that function keys path.
Also a good time to take a resistance reading from finger # 9 to the foil just above that via as it passes beside the BLUE E-cap, with the need of the ohmmeter probe to pierce thru the green resist insulation of that foil. Expecting the combined series resistance to be about 2x the prior single shunts reading.

PART 2 . . . . . FLOW PATH

Starting at the bottom via of that AC key and passing straight down, where I have superimposed the foil path where the battery symbols white info was covering it up. Then it takes a left slant and connects to YELLOW markup via set and their jumper.
There is some critical viewing here to be seen, so I only used a partial YELLOW markup.
Now, starting at that right via and viewing in side the WHITE rectangle and looking to the left . . .YOU . . . in HAVING the board in your hands, might find some foils that I do not / can not see, but I FIRST see the WIDER battery + via, that sort of forms a 3/4 loop, being opened at 9 o' clock and 12 o' clock positions. Coincidentally there are a pair of smaller foils that come in from the left and then loop around inside of that shape made by the wide foil of the battery + and they look mighty crusty in their path within that circle and again , bad areas, starting up beside the battery holder .
Now back to the YELLOW resistive jumper across the vias, its left via has a flying small gauge wire soldered to its foil, right at the via at my YELLOW A markup.
Then that wire "flys" up and diagonally travels left to my YELLOW A ' ' ' , where it gets soldered to a foil that then goes straight up the board and makes a hard right bend and then goes into finger #18.
Now, going back to the YELLOW A connection " branch off ".
Surely the original foil path was having A to be connected to foil A' and then pass to the left and upwards and eventually end up where the A''' wire is now tied in.
So I would now make a resistive evaluation of the resistive jumper between both the YELLOW via connections.
Make one probe piercing at the foil in the "CP6" area and then another probe at the A solder connection to see if the usually expected resistance value is present.
And then, take a reading of the final straight wire and foil connection from YELLOW A to the finger #18, expecting only wire and foil resistance . . . and it being LOWWWW.

That is constituting a complete flow path for your AC key.
I'm more suspicious of PART 2 connections.

DETAILED . . . . . MARKED UP PHOTO REFERENCING . . . . .
Fine detail contained , so large sizing is preferred . . . . . so, it is also being co-hosted at:
https://i.postimg.cc/SkBFwL2t/Casio-Calculator-Keyboard.png
(For as long as that lasts . . . . ?)
Also, you might want to half size and open up in two separate windows . . . . .to be able to simultaneously cross read between text and photos.

Casio-Calculator-Keyboard.png


Casio-Calculator-Keyboard 50%.jpg

( LOOKS LIKE YOU MIGHT HAVE TO USE THE TOP HOT LINK, ABOVE )

Thaaaaaaaassit . . . . .



73's de Edd . . . . .


A lady went to see her doctor.
"Doctor, every morning when I get up and I look in the mirror I feel like throwing up.

. . . . . . What's wrong with me?"
He said: "Nothing, your eyesight is perfect."



.Moderators note : uploaded reduced image.
 
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