HP41 display clean up

[Wolfgang]

I would greatly appreciate some tips and tricks for the following problem.
I got recently a HP41CV from ebay and the seller had good intentions when he was putting the calculator in the original pouch before he packed everything up and send me the calculator.
Now the pouch looks flawless, probably never was used.
However the age of it took it's toll and some of the inner fabrics have turned into a fine brown dust.
This dust went everywhere in the calculator. I tried my best to clean it out but some of the particles are now between the LCD and the plastic cover of the display.

I tried to use compressed air to blow it out but the static of the particles make it stick to the display or I just blow it from left to right.

Any way to get to it?

I did not dare to yank on the LCD to bend it backwards.

Does anybody know if I can do this safely or do I then ruin it?
Or is there a trick to get the plastic cover of the display off?

Any other suggestions how to get this little devils out there?

[Dan Grelinger]

Wolfgang, The 'big question' is; is your HP-41 a full-nut or a half-nut?

For the half-nut, the best way I have found to clean the display is to disassemble the unit and rinse the calculator top (display/keyboard/processor) vigorously under tap water for many minutes, and then vigorously rinse well in distilled water for many minutes, ensuring that all of the minerals have been rinsed from the unit, and then shake / shake / shake to remove as much water as possible, and finally to dry in a dry air environment with fans blowing on the unit over night. Once dry, the unit can be reassembled. This has the advantage of also cleaning any dirt and dust from the keyboard. On a few occasions I have had to repeat in order to ensure that the keyboard contacts dried cleanly such that the keys worked reliably, so don't replace the rubber feet until perfect operation has been confirmed.

For the full-nut, I have carefully desoldered the display connection tabs from the keyboard circuit-board, removed the display and cleaned both the top of the LCD and the back of the display glass, and then re-soldered the display connection tabs to the keyboard. This was very successful for me.

For both methods, it is a good idea to inspect the screw mounting posts and recessed screw holes and repair any damage with plastic welding cement. I have used the 'hint' to use the rubber O-rings used for card reader repair to hold cracked posts tightly together when being glued.

As an aside, it is for this reason that I ship all HP-41's that I sell in a zip lock bag, even if protected by the original case.

[aj04062]

I have doused the end only of an opened unit in hot water before, sloshed it around, shaken, then heated with a blow drier to hasten the drying.

[Wolfgang]

Thanks for the replies .
So you can just submerge it in distilled water.
Will for sure flush out some more of the dirt.

I think I have a fullnut, my display is square not with rounded edges.

[Bruce Larrabee]

If you have a fullnut and decide you want to remove the display to clean between it and the front plastic (and you are comfortable doing delicate soldering jobs) then use a low wattage grounded soldering tip. Say 12 watt or so. Position the calculator so that you can heat each connection at the main board (don't de-solder or damage the connections on the display board) without touching the posts of edges of the case. I heat the connection with one hand and when it becomes lose I lift it up about an 1/8 of an inch or so till it cools off with a small piece of wood (it's like a popsicle stick but much smaller) to prevent it for reconnecting while it cools. When I have them all disconnected I turn the calculator over and gently tap it to remove the display. When soldering it back in it is a good idea to remove any excess solder and re-tin the main board pads before soldering it back in place.