HP35 with "the Bug" and the CHS-EEX


Hi all,

I have one HP35 with "The Bug" and one without. The behavior of the CHS key with the EEX key is different with the buggy HP35 than the other. But I haven't found this difference written up anywhere.

On the buggy HP35, if I enter a number, then EEX, I do NOT see two digits off to the right until I type them in. On the non-buggy HP35 I see two zeros to the right as soon as I hit EEX.

On the buggy HP35 I must hit the CHS key immediately after the EEX key to get a negative exponent. When I do this I get -00 displayed, then I can punch in the actual exponent. But after that the CHS key does not do anything - I can't change the (-) to a (+).

On the non buggy, I can enter the EEX digits and hit CHS at will, reversing the EE sign each time.

Is this known behavior of some HP-35's or related to The Bug? Or is this a different problem?


-- Dan


I think that was a separate change, which occurred in a release before the famous bug fix. There were at least three public releases of the HP-35 firmware.

If you ever have occasion to open them, please note the part numbers on the ROMs (round metal cans, part number 1818-xxxx).


The ROMs for the one with the bugs are:

K7239FC 1818-0020
K7233GJ 1818-0017
K7231BF 1818-0006

The numbers are on the side, not the top.

Is there a document describing in detail the different ROMs sold and the bugs or errata in each set?


-- Dan


There are at least three public releases, and possibly four. There were internl engineering releases, of which it is possible that some prototype units may exist.

Prototypes: combinations including 1818-0001 through 1818-0019

Earliest known release: 1818-0006, 1818-0017, 1818-0020

Intermediate: (unknown, possibly unreleased)
combinations including 1818-0021 through 1818-0025

Bug fix: 1818-0024, 1818-0026, 1818-0027

Revision, purpose unknown: 1818-0024, 1818-0026, 1818-0028

Peter Monta has dumped the (6, 17,20) set, and a later release that is believed to be the (24, 26, 27) set, so these can be compared in simulation in Nonpareil. At some point it will be a good idea to dump the sets with 27 and 28 for verification.


Thanks Eric.

This bug affecting the operation of CHS with EEX has much more user impact than the 2.03 ln e^x bug, but is less well known. Was it resolved quickly in an intermediate release before the more famous bug?

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