Knocking on HP-41s back door :-)


Hello all!

The display of my HP-41CX sometimes fades out (goes off) immediately after switching the machine on. Slightly tapping on the back (battery compartment door) usually brings it back to life. Any idea what the reason for this behavior could be?

Regards, Jürgen


Hi Juergen,

It seems a typical case of weak contacts.

There are several points inside HP-41 that may lead to such a behaviour.

- Battery <> I/O block, (both coconut and halfnut), often caused by battery leakage corrosion, or mechanical damage in the I/O block battery terminals/or battery compartment springs.

- I/O Block <> Keyboard (both coconut and halfnut), more likely caused by broken post in the upper screws, or battery leakage corrosion.

- CPU board <> Keyboard (only coconut -AKA fullnut-), caused by broken post in the lower screws, or damaged "zebra" strip (be it polymer or metallic)

- LCD <> LCD control board (coconut, very unlikely on halfnuts) again damaged "zebra" strips are the more common cause.

If your I/O block is clean and shows no traces of corrosion, my advice is to take your HP-41 apart and check for broken/cracked screw post(s).

Hope this helps.




there is also a capacitor that might be responsible for a similar behavior. I had one HP41C with a similar problem and this is the thread after it. Hope this helps.

Luiz (Brazil)

Edited: 5 June 2010, 6:18 p.m.


Hi Diego, Luiz,

thanks for your inputs. It helps a lot to localize the problem!

Best Wishes, Jürgen

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