Interesting HP-65 card reader failure mode

[John Garza (3665)]

To summarize for those jumping in at this point:
2 issues at work.
1) HP65 #1333A09948 reads a card and mistranslates the program steps.
2) a couple of Teenix HP65 CPU cards insert a STO 4 in memory when reading a card.

Some more information on HP65 #1333A09948 running with the original CPU:

1) Replacing the 15uF capacitor on the sense/amp board did not work.
2) Head resistances are 50.5 ohms each (Red-Yellow and Orange-Blue wires)
3) Replacing the 5.6K speed control resistor on the sense/amp board with an external 10K multiturn pot produced some odd results. Settings near 5.6K reproduced the error. Slight deviations in the setting produced different codes, twice it produced the correct codes, but these could not be repeated on subsequent reads. Settings far beyond 5.6K on either side produced flashing zeros, or 'memory full' displays (negative signs) with either 35 01 or 41 codes in memory.

-J