HP-35 switch


Hi everybody.
I rebuilt a pack for my Classic (HP-35 serial 1346A05451), and I finally got it working!
The only thing is that, to keep it on, I have to slide the switch AND press it down firmly.
I guess it's a matter of cleaning the internal contacts, but I don't know hot to open it and how to clean (i.e. which substances to be used and which not): may you point me to some resource (if any) or give me any hints?
Thank you all for your help.


There are 2 screws holding the bottom case on, 2 in the battery compartment, 2 under the front feet, 2 under the label. Take them all out and lift off the bottom case. When refitting it, note that the gold-plated contact must fit in front of the charger connector pins, and short the outside 2 pins together.

Now lift off the logic board. It is static-sensitive, and replacment parts are difficult to get, so handle it by the edges and put it in an anti-static bag, like the ones PC expansion cards come in.

Undo the 8 screws along the sides of the chassis plate. Lift out the plate and keyboard/display PCB. This is less static-sensitive than the logic board, but still treat it with care.

At this point all the keys are loose in the top case. Be careful not to drop it.

You can now see the power swtich. There are 2 pads on the circuit board and a gold-plated spring contact that often sticks to the PCB. Remove it, clean the pads and contact with propan-2-ol (isopropanol, isopropyl alcohol). Put the contact, flat side down, in the switch slider in the top case.

HP put a smear of silicone grease on the switch contacts. It will reduce wear, but it may also cause contact trouble. Whether you do it is up to you.

Put it all back together.....


[pre]Tony, thank you very much for the "film" of the intervention.
I'll try your tips as soon as possible!

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