Strange HP-35 auction on TAS


I just saw this rather strange HP-35 for sale in a TAS auction. It's strange because it presumably is an early version with "the bug" and the s/n is consistent with an early version 2. However, the keyboard and case front appear to be a later version 4. The rear label appears to be undisturbed. It's almost as if someone mated the internals and rear case from a buggy version 2 to the front case and keyboard of a version 4, but I don't know how it was done without any evidence of damage to the label. Anyways, I thought y'all might find this interesting.


Definitely a Franken Calculator.

I got quite good at removing the back label and replacing it without leaving much trace. It can be done, but this example is quite excellent. Could be a repro but repro's I have seen are just slightly thicker.

IIRC there should be a short label between the lower rear feet on a Type-2 back.


The thicker repro labels I bought from Ben Ong do not have the text at the bottom, e.g. "Made in U.S.A., 3.75V 500mW", but instead the thin silver border line is continuous. All HP-35 versions have some sort of label at the bottom, either a s/n or a label "Hewlett Packard 3.75V 500MW Made IN .... PATENT PENDING". Also, that serial number is quite unusual in that the prefix 1143A is typed, not printed in black, and the 1s are Is.

Edited: 16 Aug 2011, 9:50 p.m.


Yea, good catch. I've never seen an HP-35 serial number label all typed like that.


The serial number puts it in the range of early V2s with the serial number attached between the lower feet, as does the bottom part of the case. The sticker looks legit.

However I am a little bit concerned about the ln bug, this should not be present in a factory repair unit - but they did a ROM replacement on the customers PCB for the bugged uints, maybe they ran out of parts?

Btw. there have been original labels on ebay (a couple), so it's not impossible to recreate a 35 - but due to the limited value of a non-red dot, that's a pointless effort.

Alltogether an interesting unit, but probably only for a hardcore collector :)


The SN label is an HP replacement and as such, the unit was most likely a service exchange unit. I'd bet the unit is all V4, inside and out, and does not have buggy roms. Nothing remarkable, they did this all the time, back in the day.


But how can you explain the serial number, itself ? The prefix 1143 was used only on the version 1 (Red Dot) and early version 2. By the time the version 4 came out, the s/n prefix, which is presumably a date code, had been changed to a later value. And would HP type a capital "I", instead of the numeral "1" on the label ? As to the bug, well I guess only the eventual buyer will know for sure.


There are service replacements of later HPs known without a serial# burnt in, instead the original serial# has been stickered on. So I assume this is common practise (concerning the inventory tracking of larger companies, this is the easiest way to go).

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