HP-67 ROM 1818-0551 broken



I have a HP-67 with a (probably) broken ROM 1818-0551. The symptoms are as follows:

When started it shows

"0.           00"
in the display. If you type any number, e.g. "5", the display shows
if you then type "Enter", the display shows
"5.           00"
You can calculate with this, i.e. hitting the sqrt key gives
"2.           00"
on the display. So basically the machine looks quite ok, except that it is not in FIX 2 mode after starting, and entering numbers does not work.

Measuring the interconnections shows no Problem, i.e. all ROMs, the ACT and all others seem to be interconnected just fine. Measuring the separate signals on an Oscilloscope and also with a Logic Analyzer shows no abnormalties.

After that I desoldered the ROMs one after another to figure what is wrong, and found that when the ROM "1818-0551" is taken out, the calculator still starts and behaves the same as described above.

From this I assume the 1818-0551 ROM is broken. Does anyone here have one of these ROMs as spare, and would be willing to help me out with this? I would pay for the ROM.

Any help, hints as what else this could be are very wellcome!



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