HP-67 1705A1636 very bad oxidation looking for suggestions

[albertofenini]

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

[teenix]

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 :-)

cheers

Tony

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

[rprosperi]

(12-30-2020 12:04 AM)teenix Wrote:  PS - Finally back home today after 7 months :-))

Welcome home Tony!! I'll bet home never felt so much like home. Good to be home for New Years, and hopefully it's a better year, though could hardly be worse.

[[kby]]

Cleaning: that looks more like rust (iron oxidation) rather than most of the material for the calculator. I might try a fiberglass circuit board prep pen on some if that. Do it over a trash can or the broken fiberglass gets everywhere (itching powder). This looks like the kind I use:

https://www.autobodytoolmart.com/product...acQAvD_BwE

I might start with something other than the recording head. Some solvent like alcohol and a soft cloth with some gentle rubbing will hopefully remove the stuff as it doesn’t look like it came from the head itself. Same may work for some other areas you can get to and support whilst cleaning.

Repairing traces: depends on the extent. The stuff here:

https://www.soldertools.net/categories/P...Materials/

Can, I think, theoretically do a nice job. However their older method with the epoxy leaves the trace hard to redo if you make a mistake. They have some new dry film adhesive stuff that looks more promising but I haven’t tried yet. This is particularly important because we usually have multiple fine and close together traces that are damaged in the corroded area an I find the epoxy method very hard to do in that kind of situation. So, I think this is a good idea but I can’t actually say I’ve had more than limited success. Wires are easier, but this has the potential to look nicer with practice. But it’s not that cheap either. And it works best if the area to be reconstructed is straight. I haven’t found a good way to do custom bends cleanly.

[Massimo Gnerucci]

(12-30-2020 12:04 AM)teenix Wrote:  PS - Finally back home today after 7 months :-))

Whoa! That's a long trip away. Aviators like seamen?
Welcome back then, and a Happy New Year!

[teenix]

(12-30-2020 08:10 AM)Massimo Gnerucci Wrote:  

(12-30-2020 12:04 AM)teenix Wrote:  PS - Finally back home today after 7 months :-))

Whoa! That's a long trip away. Aviators like seamen?
Welcome back then, and a Happy New Year!

Many thanks and a safe and prosperous new year to you.

cheers

Tony

[albertofenini]

Welcome back home Tony !! that was a long one !
Thanks everyone for all the ideas, we'll try something over the next days and we will keep posting
Happy New Year everyone and let's hope for a better year !!!

[albertofenini]

It must be said that the original keyboard was beyond repair or at least not repairable in the short term.
We may be investing few euro in a conductive pen to repair the corroded traces but those good cost quite a lot
Also the metallic domes needs to be removed and cleaned underneath to make it reliable

Because of this we used a old keyboard from another HP-67 which was also repaired

Particularly under the RCA chip there where two missing traces, one from the transistor that sits between the two
chips and one underneath the RCA chip itself that we fixed with a couple of thin cables

Also the card reader board that came with the unit was not reparable, we tried using thin cables but the result
was not working and so we used a board less damaged

The magnetic head we tried was not working although in a good preserved case so we used a different one
but that fact that bakelite was not as smooth as it should have been together with the copper pieces that should keep
the card aligned is making reading and writing not consistently

Last but not least, the Logic board has some oxidation, that in the long term is going to worsen,
however, last time we washed a working Logic board from an HP-67 it came out like new but it was no longer
working, so we are a little skeptical with this ...

All in all we are learning a lot from this and we'll do our best to bring it back, as always thanks to all the suggestions and tricks !!!

Let me say that the building quality of the HP65 is far far better than that of an HP-67 ...

Some additional pictures can be seen here

HP-67 1705A01636 2nd part