HP 35 ROM fault?

[PANAMATIK]

(11-21-2016 10:52 PM)Harald Wrote:  ... Would anybody know which instructions are only use by those four functions and which of the three ROMs that would reside in?

Cheers,
Harald

One of my HP-25 calculated wrong sin, cos and tan results. As it turned out it was a single bit ROM error.

Recently I read the classic ROM code from an HP-70 by interrupting one single PCB path and attaching four wires to a PIC working as a address scanner. You could read the ROM code of your HP-35 and compare it with the original.

More interesting question is how to repair the ROM chips. An idea could be to add a tiny processor, which listens to the addresses and corrects the false bit by pulling down the serial data line at the right moment.

Bernhard