Non-invasive switch repair for Classic?

[John R]

I recently acquired an HP-70 (finally!) that is in absolutely beautiful cosmetic condition, but that unfortunately exhibits some on/off switch flakiness common to vintage Classics. In particular, although the switch feels solid, gentle rocking of the switch in the "ON" position produces various kinds of aberrant behavior, ranging from illumination of random display segments to alteration of the display format (i.e., what would normally be achieved using the DSP key).

I am wondering: has anybody ever heard of any non-invasive repair or "therapy" to fix or mitigate this problem on a Classic? In the past I have opened up Classics to fix this sort of problem, but I've never gotten the back label to look as nice as it did before I started. Given the beautiful condition of this calculator -- and the rarity of the HP-70 -- I am reluctant to pursue such a solution here. Any advice would be much appreciated!

[Thomas Radtke]

(12-14-2013 07:38 PM)John R Wrote:  In the past I have opened up Classics to fix this sort of problem, but I've never gotten the back label to look as nice as it did before I started.

Same here, and I was very careful.

My advice would be to leave your sample as it is. After all, you're probably not going to use it on a regular basis. If you must do something about it, I'd recommend bathing it in 70% EtOH and operate the switch while doing so. Didn't try this myself, but have done such cleanings a couple of times without damaging anything.

It needs to dry for *days*, if not a week, depending on the r.H.

[Geoff Quickfall]

Whoa nelly!

The best way is to disassemble the entire calculator.

If not; using an eye dropper, drop some rubbing alcohol on the switch and then work the switch. HP Used a conductive silicon paste which turns into a great insulator over time. Once the switch is functional then introduce a small amount of DeOxit gold via eye dropper or can with the red straw.

The whole idea is not to splash solvent on to the facia plate (key surround).. Sometimes the lacquer finish is so degraded that even water will cause a white bloom.

Check this posting and scroll down to the pictures. It will show you how to remove a label then restore it to factory fresh non wrinkled form. Also discusses the switch problem.

Hp 45 restoration

And yes the book is being completed as we speak

Cheers.

[Massimo Gnerucci]

(12-15-2013 02:56 AM)Geoff Quickfall Wrote:  And yes the book is being completed as we speak

Ca$h in hand!

[Diego Diaz]

Hi Geoff,

Hope you still have the waiting list handy... and my name on it!

All the best.

Diego.

[John R]

Thomas, Geoff: thank you both for your suggestions. I think that for the moment, I will leave the HP-70 alone. However, I think I will practice Geoff's label-removing techniques on one of my old HP-45s -- I have two that are in pretty beat-up shape, and they would make good surrogates to hone my skills before trying my hand on a more prized specimen.

Also, Geoff, like many here, I'm eagerly awaiting the completion of your book!