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HP-67 1705A1636 very bad oxidation looking for suggestions
12-30-2020, 12:04 AM (This post was last modified: 12-30-2020 12:58 AM by teenix.)
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RE: HP-67 1705A1636 very bad oxidation looking for suggestions
Maybe some baking soda mixed with water (de-ionised probably better) into a paste to clean the PCB. This should remove any acidic problems, but really only practical on un-populated boards.

Scrub with a soft tooth brush. Dish washing liquid diluted with water cleans the board with little or no residue then dry thoroughly with hair dryer or a warm oven, then afterwards only handle the board by its edges.

You can use a PCB lacquer to protect the board after cleaning which will also allow re-soldering. (Note: Not on board surfaces used for keyboard or card reader contacts)

Whilst it is a fiddly process, I have used lengths of stripped wire-wrap wire to rejoin broken tracks in the past. Once the insulation is scraped away it has a very small diameter and is plated. The problem with track corrosion is that solder may not take properly or the track remnants may lift from the board from the heat. If there is any manufactured protective coating over the tracks, that will have to be removed.

Has the plastic warped at all around the card reader.

The "a" key has died on my laptop. I have to paste an "a" into the text every time. I didn't realize how many time I used that letter. Of course it couldn't be a "Q" or similar :-)



PS - Finally back home today after 7 months :-))

(12-29-2020 09:33 PM)albertofenini Wrote:  Hi Everyone

We bought this for few reasons : it was cheap, the faceplate was in very good conditions,
it had a battery door and you never know what you can find inside

Turns out that the logic board, once put in a clean unit, was working

Everything else is close to garbage, but it was no surprise as it was plenty of pictures

We began a deep cleaning process with 50% vinegar, 50% hot water
The result can be seen in the pictures
At this point we would very much appreciate some hints from who is more expert than us

Should we proceed what's your best suggestion for :

Rebuilding missing pcb traces (there a few missing on the keyboard board and on the card reader board)
What do you use for that ?

The bakelite was very much deteriorated and although it can be clean well, it is not as smooth as
it should be. We have found this to be a problem particularly in the card reader, as the card is not
passing as it should be, sometimes it even stops in the middle because of the friction

Has anyone succeeded in renovating this ?

Last but not least, after the vinegar treatment and after the alcohol isopropyl rinse, even when a pcb looks clean,
when it dries a kind of oxidation more like limestone shows up, how do you get rid of it ?

Thanks for any technique you would like to share with us

Pictures can be seen here : HP-67 1705A1636 very bad oxidation looking for suggestions
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RE: HP-67 1705A1636 very bad oxidation looking for suggestions - teenix - 12-30-2020 12:04 AM

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