I managed to draw the schematic of Texas Instruments SR-56.
Here you can download the schematic.
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. |
Correct FW on left and dumped FW on right |