Suna

Casio CFX-9850GB Plus WE (White Edition) released in 2002

General parts view.

Processor PCA and Keyboard/Display PCA.

Contrast preset potentiometer.

Processor PCA. Main components:
- Hitachi HCD62121 Processor as per Wikipedia (reference not visible as it is sealed & hidden)
- BSI BS62LV1024-70 128KByte SRAM 70nS
- OKI MR27V802D 1MByte PROM 100nS
- MC74HC4066A CMOS Quad Analog Switch
- 4.3MHz xtal with embedded caps set

SRAM reconfiguration to 64KByte.
The CFX-9850GB Plus WE has a SRAM factory set to 32KByte. However the SRAM chip has 128KByte capacity.
Public information at several places states that it is possible to "upgrade" the SRAM size by changing the RAM setup jumpers. I read about it here.

Factory set to 32KByte: R20 jumper out, R21 jumper in.

Enable 64KByte: R20 jumper in, R21 jumper out.

It took me two minutes to to switch the jumpers. It was that easy and it is working fine on my machine.
Other machines may experience issues if the SRAM chip is defective.
Therefore it is essential to run the self test a few times to validate the new SRAM size good operation.

Basically I have unsoldered the jumper from R21 and soldered at R22 position.
This jumper looks like a SMD resistor but it has a zero Ohm value.

Assembling the calculator.

The Reset push button membrane and key contact.

The PCA is fixed using a few screws. No snap in / latches / rivets are used here.
Really a pleasure to work with when maintenance is required.

Idle current consumption: 2.5mA from 4 x AAA battery cells (6VDC).

Reconfirming that the new 64KByte SRAM sizing is recognized.
61396 Bytes available to the user.

Running again the self test by pressing F6 + a b/c + AC/ON.

This calculator shows this model code: GY357

Testing the 8Mbit PROM.
ROM version 1.0. Four byte checksum = 0642FEA8

Testing the new 64KByte SRAM configuration.
RAMaddress = F7FF

Write/Read pattern: AA (a basic h/w test using a 10101010 binary combination).

Color LCD by CASIO.
Changing the contrast changes the temperature of each color. To see the Orange, Blue and Green colors will require a specific contrast setting, despite being possible to adjust the three individual colors as well.