HP-67 weird behavior after reading a card

[teenix]

Hi Alberto,

When pressing GTO.112, just after pressing the [2], these ROMs execute...

ROM 00 - 1818-0268
ROM 02 - 1818-0268
ROM 03 - 1818-0268
ROM 04 - 1818-0550
ROM 05 - 1818-0550
ROM 07 - 1818-0550

as well as 1818-0231 and 1818-0232 which you already replaced

These RAM locations are also accessed...
32
48
61

... but you already replaced the ICs for this RAM range, 1818-0231 and 1818-0232

ROM0, 1818-0268, is executing common key press code, so maybe this is ok if you are sure the normal key functions work.

Most of the processing for error checking of the entered value (112) and then jumping to the entered step seems to be executed in ROM 04, 1818-0550, so maybe this is faulty.

As you have 1818-0226 in the donor board, you would have to replace the 1818-0550 with 1818-0226, and 1818-0551 with 1818-0228.

It is hard to say where the fault lies without analyzing the Is and DATA buses.


Edit:
Just looking at 97 service manual and it mentions inconsistent program stepping faults point to ROM 1818-0550 also.


cheers

Tony