Restoring a HP9830B calculator.

[MattisLind]

This problem kept me thinking and looking in the schematics.

I wasn't at all sure that it was a RAM or ROM problem since when I set it to FLOAT11 precision and entered 1000000 it responded 3.22222222222+E6. It was handling the exponent all right but the mantissa was wrong in each digit. The fact that it actually added two to each digit (22222 became 44444) turned my eyes to the ALU ROMs.

I checked the BCD ROM but it was exactly as the dump provided by Tony. One funny thing was that the machine could run BASIC programs without it! Although calculations gave even stranger results.

Then I checked the main ALU ROM. The first 128 nibbles read all right. But the last 128 nibbles were the inclusive OR of the corresponding nibble in the first half! Checking the schematics shows that the upper half is addressed by the BCD flag. So it makes sense that BCD arithmetics isn't working but all normal arithmetic works fine!

I ordered a replacement PROM from Bulgaria, programming of the chip was included in the price! Although I think it should work with the Data IO 29B I have here, I have had some difficulties in the past with some Harris chips that it were not able to program and I never tested to program a Signetics chip in it.

Hopefully this solves the problem.