SHARP EL-9000 keyboard flex PCB repair

A time ago I acquired interesting scientific calculator SHARP EL-9000 to my collection.

SHARP EL-9000

 But as I expected the flipping keyboard did not work at all. The reason was broken connections on the flex PCB where it is being bent. I tried to fix it with the conductive glue but it didn't work. 

Broken connections

So I decided to recreate the whole flex PCB. I removed it from the aluminium board. 

Keyboard flex PCB

Then I scanned it and used as background in the KiCad to be able to create original traces. The Chinese PCB manufacturers offer relatively cheap flex PCB services so I sent them data of finished PCB.

"Digitalizing" the flex

And this is the result. I was very satisfied with it

New flex arrived

So I installed the new flex to the calculator and tested its functionality.

Flex installed to the keyboard

The keyboard works perfectly. Now I am also able to use the printer CE-50P compatible with this calculator. Before the fix it wasn't possible because to start printing you have to press OPTION button which is located on the flipping keyboard.
 

And the keyboard works

Now I can also use a printer

Texas Instruments SR-56 schematic

I managed to draw the schematic of Texas Instruments SR-56.

SR-56 schematic

Here you can download the schematic.

HP-48S faulty firmware resurrection

I got this HP-48S for a few bucks. It was so cheap because it wasn't working. When I turned it on it showet just some random picture.

Picture after power-on.

So I started fixing. First I tried to replace the resonator, no change. Then I swapped RAM with no success. So the last option was the faulty ROM. After some research I found out that the ROM is uPD23C2000GC. So I desoldered it and made an adapter for programer and dumped the content of ROM. You can explore it here, it is file ROM_orig.BIN. It is firmware version J as can be seen at the end of the file.

Original ROM ready for dump.

I compared the dumped content with correct firmware and it revealed that on some addresses there are swapped MSB bits.

Correct FW on left and dumped FW on right

Then I connected a socket for new ROM, actuly it will be a Flash. I chose SST39SF040 in PLCC package.

Socket preparation.

Socket with Flash in place.

I progrmmed the Flash with firmware version J and voila, it is working. Now I can program any firmvare version for this calculator (ROM_A to ROM_J) and it works.

Firmware version "J"

Firmware version "A"