Texas TI-59 reading card error

[Hiwi]

This is an very old post, but there was never posted a solution.
I had similar problems with REV 3 Boards, and as mentioned in the service manual you can solve this problem in most cases with a slight modification.

Open the calc, take out the main pcb and locate the pin 21 of the display (last pin, leftside, pin 1 is marked) cut the connection cautious and connect the open ends with a diode, TI stated a PG1922, but it is not available anymore. The replacement is a NTE512 and this is a standard 1N4148!

Other problems when reading may be solved with some (4) small 100-150pf capacitors soldered from pin1 to pin2 ... on the cardreader connection on the main PCB.

I saw this mod only once on an Rev 5 board.

Ralf