Casio fx4000p repair question

[Tugdual]

I just completely serviced a Casio fx-4000p and after the reassembly, it didn’t switch on. I found on some pictures that there is a small white dot near the on switch which seems to pressure the switch film against the board. I added a piece of tape there and indeed the calculator operates well now. Can sbdy give me more detail about that white thing? What material is it, how does it stick to the film? I haven’t seen it while opening the calculator.

[Dan C]

I have an fx-4000p also, but i have never actually figured out how the power switch works.
Not much help for you, but i assume you have seen these great pictures from jebem?

http://2.bp.blogspot.com/-9s28vY7K15A/Vm...0P_018.jpg

Full tread: https://www.hpmuseum.org/forum/thread-5278.html

[Tugdual]

(12-28-2022 06:11 PM)Dan C Wrote:  I have an fx-4000p also, but i have never actually figured out how the power switch works.
Not much help for you, but i assume you have seen these great pictures from jebem?

http://2.bp.blogspot.com/-9s28vY7K15A/Vm...0P_018.jpg

Full tread: https://www.hpmuseum.org/forum/thread-5278.html

Thanks Dan, yes I had seen these pictures and this is where I found I was missing that part. See the carbon film with 3 strips and a white dot? The the white dot is missing on mine and I wonder what it is made of. It seems to ensure that the main board is pressed against the carbon contact.

The whole switch is a weird choice it is simply a carbon film pressing the board and shorting two points on the main board in one position. I guess this is introducing a lot of resistance in the main power circuiit.

[Dan C]

(12-29-2022 08:20 AM)Tugdual Wrote:  Thanks Dan, yes I had seen these pictures and this is where I found I was missing that part. See the carbon film with 3 strips and a white dot? The the white dot is missing on mine and I wonder what it is made of. It seems to ensure that the main board is pressed against the carbon contact.

The whole switch is a weird choice it is simply a carbon film pressing the board and shorting two points on the main board in one position. I guess this is introducing a lot of resistance in the main power circuiit.

I can open my fx-4000p and take a real closeup picture on that white dot thing, and then maybe we can figure out what it is, and what it can be replaced with.

[Tugdual]

(12-29-2022 06:45 PM)Dan C Wrote:  

(12-29-2022 08:20 AM)Tugdual Wrote:  Thanks Dan, yes I had seen these pictures and this is where I found I was missing that part. See the carbon film with 3 strips and a white dot? The the white dot is missing on mine and I wonder what it is made of. It seems to ensure that the main board is pressed against the carbon contact.

The whole switch is a weird choice it is simply a carbon film pressing the board and shorting two points on the main board in one position. I guess this is introducing a lot of resistance in the main power circuiit.

I can open my fx-4000p and take a real closeup picture on that white dot thing, and then maybe we can figure out what it is, and what it can be replaced with.

That would be very much appreciated if you have an opportunity but please don’t damage your calculator for me. Happy new year!

[Dan C]

(12-31-2022 01:04 PM)Tugdual Wrote:  That would be very much appreciated if you have an opportunity but please don’t damage your calculator for me. Happy new year!

OK! Give me a couple of days, and i will try to get some good pictures!

[Dan C]

Damn! I'm no good photographer, and the pic's are to big to attach here

Do you want me to e-mail them?

[Tugdual]

(01-03-2023 05:51 PM)Dan C Wrote:  Damn! I'm no good photographer, and the pic's are to big to attach here

Do you want me to e-mail them?

Hey Dan, whatever works for you but would be better to have them here for other potential users. Could you identify what the dot is made of?

[Dan C]

(01-03-2023 09:39 PM)Tugdual Wrote:  Hey Dan, whatever works for you but would be better to have them here for other potential users. Could you identify what the dot is made of?

As far i can tell it's a bit of white plastic, or maybe some ceramic material.
Very thin, maybe just 0.3 mm or 0.4 mm.

I managed to make the pictures smaller, but they arent that good i think.
Anyway, here they are: