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I would need to know the exact dimensions of the screws (diam., length) inside the HP-35 battery compartment. In my 35 one screw is missing, the other got replaced by a silver color screw in an apparent attempt by a previous owner. I do not want to remove resp. destroy the intact backside label to check with the remaning screws. I hope to get such screws as spare part, although I live in the metric world....

Thanks & regards,

Andreas

Quote:
I would need to know the exact dimensions of the screws (diam., length) inside the HP-35 battery compartment. In my 35 one screw is missing, the other got replaced by a silver color screw in an apparent attempt by a previous owner. I do not want to remove resp. destroy the intact backside label to check with the remaning screws. I hope to get such screws as spare part, although I live in the metric world....

Thanks & regards,

Andreas


If one screw is missing, I'd probably lift up one of the feet and unscrew the one from there and move it to the battery compartment. I doubt the calculator will notice the one under the feet missing.

Or I'd take the screw to the largest nearby hardware store and try to match it with what they have. I matched a HP-97 screw very closely in the wood screws section.

First, these are self-tapping screws and not machine screws. They tap the threads into the plastic posts in the case when they are first installed at the factory. I measured a few with a digital caliper, and they are approximately 7.2mm long and 2.2mm diameter. The thread pitch is very approximately 0.8mm, but I don't have a proper pitch gauge to measure this. The replacement screw may be bigger, in which case the original screw will no longer be a tight fit. I fixed this in one calc that had been previously opened by using a longer screw to make some new deeper threads.

Regards,

Michael

Quote:
I fixed this in one calc that had been previously opened by using a longer screw to make some new deeper threads.

That is in fact the official repair technique right out of the HP service manuals.

Thank you for the fast responses. First, I "reuse" the screws under the rubber feet for the more visible locations in the battery compartment and then I check for new screws of suitable size in the next hardware shop.

Andreas

HP did in fact use silver colored screws in early 35's so I would not assume it was an owner repair, more than likely it was original if the the pitch was the same as other screws inside the unit. FWIW, many 35's had a mix of both black oxide and silver colored screws.

I don't know what luck you'll have finding a metric substitute since the originals are a standard U.S. numbered screw size and further, they are of a unique self tapping design specifically for plastic and are sold under the trademarked name "Plastite".

Interesting to learn that screws of different colors were used even within the same calculator, I did not know that.

Meanwhile I got in a hardware shop silver color self tapping screws of 2.3x8mm, pitch 0.8, should be a suitable replacement.

greetings,
Andreas

Edited: 10 Oct 2009, 11:07 p.m.