Non clicky HP41 key

[ElectroDuende]

Hi,

I'm restoring a Tall keys 41C. Initially it only had one problem; a badly corroded flex circuit, buth thanks to Diego that has a remedy.

Next problem is in the keys... [1] and [2] barely click although they register properly; but [3] doesn't click at all, and even miss some keystroke from time to time. Rest of the keyboard functions wonderfully.

I have seen over ebay people selling the domes but it seems that reaching the front part of the PCB to replace them is quite a destructive process, and I don't feel confident about this... Even the removal of the logic board scares me a bit, as its the old type, held in place by two golden nuts on the screw posts, and I fear to wear the external thread of the posts.

As Geoff's book seem not to be available yet... any recommendations?

Also... is there any way to reach under the LCD protector to clean the dust, that doesn't imply to desolder it? I'm quite skilled with the soldering iron, but you know, "if it works, don't tocuh it"!

Thanks in advance!

[TASP]

I have managed to clean under the LCD without a desolder, but it had to be rough on the hardware. I managed to get some lens wipe material that was saturated with TV screen cleaner. I wrapped it around a flexible paring knife blade, and I can't recommend anyone else try that. I was able to clean mine, I did not sever a finger, but surely somebody has a better way of doing it.

I had the LCD pulled quite a ways out of alignment to do this, it couldn't have been good for any of the hardware.

(machine was not in very good shape from battery leakage, so I was willing to get tough on grime with it, there was considerable poo on the glass but I got it all off)

[Geoff Quickfall]

The book the book the book, soon. :-)

Your 41c:

-LCD: cleaning, best way, desolder at the PCA side, then damp cotton cloth to clean underside of lens and the top side of the LCD. Place bracket and panel back, solder the far left or right contact in place, observe alignment-adjust and when satisfied solder the other far right or left contact thus securing the alignment at the opposite ends. Check again!!! Then solder remaining points. I use a three aa battery solder iron with fine point, very hot but for a short period and use flux.

-keys: fixing domes involves removing all the heat stake tops (NOT ADVISED FOR THE FAINT HEARTED) sorry for the shouting. The hard part is leaving enough of the heat stake behind to remelt a cap. The REALLY hard part is soldering a replacement dome from a donor into place. Repairing the dome with solder has been tried but will fatigue very quickly. My suggestion is to live with it if still contacts. I know, not satisfying but what can you do? Getting a bouncing key repaired involves a drop of deoxit gold introduced into the tiny 'pore' associated with the offending key and then simply; pressing the key repeatedly. Deoxit actively restores the contact and removes corrosion, then protects the contact. It will fix the continuity problem but will not fix a cracked dome; which is the reason for no click.

-PCB/PCA Board: the problem with the nuts as they were self tapping. Re screwing them may cause the post to be stripped. HP when repairing them would substitute a smaller diameter nut. Typically this repair was a one off. Along comes you and I. We will remove and replace multiple times troubleshooting and perfecting. So here is a repair is the nuts become cross threaded and stripped.

This is a tall keys to 41c conversion with stripped PCA threads for the nuts. Scroll down the posting to see how I substituted the nuts with silicon tubing, the same tubing used for card reader repairs:

http://www.hpmuseum.org/cgi-sys/cgiwrap/...ead=186130

Scroll down to see keyboard heat stake and 'pore' pictures:

http://www.hpmuseum.org/cgi-sys/cgiwrap/...869#217869

Deoxit gold, google it and purchase a small tube (inch and a half long). EBay search and you will see deoxit in packets of three. I have restored a Grundig 4500 as well a a Philips philletta vintage 50's tube radios and the other two application tubes are perfect for these volume control and tube contacts.

Check out the search function as any problem that arises, chances are they have been addressed.

Geoff

[aurelio]

(07-14-2015 03:14 PM)ElectroDuende Wrote:  Even the removal of the logic board scares me a bit, as its the old type, held in place by two golden nuts on the screw posts, and I fear to wear the external thread of the posts.

personally I think that the old ones with nuts are easier in managing that the other ones, where the coupling work of the boards is made exclusively by the tightening of the posts' screws

(07-14-2015 03:14 PM)ElectroDuende Wrote:  but you know, "if it works, don't tocuh it"!

How I understand you expecially in LCD matter

[Massimo Gnerucci]

(07-14-2015 05:26 PM)Geoff Quickfall Wrote:  The book the book the book, soon. :-)

Amen!!! :)

[ElectroDuende]

(07-14-2015 05:26 PM)Geoff Quickfall Wrote:  -LCD: cleaning, best way, desolder at the PCA side, then damp cotton cloth to clean underside of lens and the top side of the LCD. Place bracket and panel back, solder the far left or right contact in place, observe alignment-adjust and when satisfied solder the other far right or left contact thus securing the alignment at the opposite ends. Check again!!! Then solder remaining points. I use a three aa battery solder iron with fine point, very hot but for a short period and use flux.

Hum... I may try this, if I find a bit of time and quietness at home (difficult with two little beasts arround).

(07-14-2015 05:26 PM)Geoff Quickfall Wrote:  -keys: fixing domes involves removing all the heat stake tops (NOT ADVISED FOR THE FAINT HEARTED) sorry for the shouting. The hard part is leaving enough of the heat stake behind to remelt a cap. The REALLY hard part is soldering a replacement dome from a donor into place. Repairing the dome with solder has been tried but will fatigue very quickly. My suggestion is to live with it if still contacts. I know, not satisfying but what can you do? Getting a bouncing key repaired involves a drop of deoxit gold introduced into the tiny 'pore' associated with the offending key and then simply; pressing the key repeatedly. Deoxit actively restores the contact and removes corrosion, then protects the contact. It will fix the continuity problem but will not fix a cracked dome; which is the reason for no click.

That is what I feared... ok, for the moment I'll keep it like that, as it only misses one keystroke from time to time... maybe I'll try the deoxit option, to see if it improves this. That is why I feared about the golden nuts, as I have to remove the logic board to reach the pinhole of [3].

Many many thanks fur such a detailed explanation. You can count with a customer for your book here ;-)

[isanchez]

Hi,
just to contribute with my experience.

During the past month I have been working in a couple of 41c, with very low serial numbers (1950xx). They implement the oldest display driver, tall keys, and if you look carefully at the finish of the keyboard mask, it is looks different to the typical 41c. It looks "painted" in a metal plate more than "printed" and the finish is very smooth.

Advice: Be very carefull when using the Deoxit, that does not touch this "painted" type of keyboard mask...or it will dissolve the letters and the black paint, and ruin the calculator ..., please take this into account. I recieved one with this problem from one friend and I had to change the keyboard mask. It is a pity because this model is very rare.

One of the old 41C was VERY dirty...I have seen and worked with dozens of HP41s, but none like this...It is very usual to find coffee or beverages residues that get "gummy"...
My recommendation: put ONLY the keyboard in vertical position (REMOVE THE BOARD APART) inside a glass of water with non aggressive detergent (like the one you use to clean dishes or wash your hands). Keep the display out of the contact with the water. Leave it for one day or more and change the water (now without soap), from time to time repeatedly press the keys, specially the most affected ...after this use a hairdryer to dry it (avoid very hot air). Be patient and dry it carefully. I have done it and all the dirtiness was removed successfully. After this you can apply the Deoxit if the remaining problem is the oxid...

[I insist: always keep the display out from the contact with the water. Only the keyboard can be in contact with the water].

Apart from this, I have noticed that the click of the row formed by "1", "2" and "3" had not the same "feeling" in both old 41c's calculators. The "click" was not as noisy as in rest of the keyboard...Now you mention that the 1,2 & 3 in your calculator behaves similar...
This makes me think that, maybe, there is something different in the design of this row in the keyboards of these 41s, or it is affected in some sense by the presence of the two lower posts...think that could be enough to improve the keys touch/reliabilty, but they will not behave exactly as the rest.

This is all,
kind regards

Ignacio