Circuit board sealent anyone?

[John Garza (3665)]

Every once in a while, I get the urge to visit the non-HP machines in my collection.

I have 3 operational TI-59s (100%op including card readers), and 5 non-op in various failure modes.

The most common fault is card R/W failure due to corrosion/failure of the mag card op-amp and associated capacitors. This happens even with a known good card reader installed. Sometimes the corrosion runs up the ribbon cables to the card reader and you have a mess on your hands.

I'm starting a project to get another 2 or so 59's up to spec. Though I never keep batteries installed, I'd like to increase the reliability. To that end I'm thinking that after I replace components and remove all corrosion, to seal the boards. This should reduce/eliminate corrosion.

Has anyone tried such a thing on calculator circuit boards? I'd like to know what I'm getting into.
Thanks!

-J

[twoweims]

I just saw this the other day and am considering giving it a try:

At ~23:50 in this video...

https://www.youtube.com/watch?v=EPO3AEg9...8Y&index=6

[KeithB]

I think air and humidity can still get through, and it prevents repair in the future. I don't know that it is a great idea.

[Maximilian Hohmann]

Hello,

since always, so to say - my grandfather told me how to use a soldering iron when I was 10 or 11 years old, I use this spray to protect circuit boards: http://www.kontaktchemie.com/koc/KOCprod...n&plang=en
A major advantage over other types of lacquer is that it can be soldered through. No idea if it can be found in the US or whether there is a similar product.

Regards
Max

[teenix]

I have used the protection sprays in the past, they work ok and as mentioned you can get solder through types. These will break down over time like most things. You have to be careful about overspray on components that won't like it, switches, sockets, trimpots etc.

If the calculators are stored away in a cupboard or similar and not used often, maybe put them in mostly evacuated plastic zip lock bags with silica gel packets in the battery compartment.

cheers

Tony

[John Garza (3665)]

(10-27-2023 08:34 PM)teenix Wrote:  If the calculators are stored away in a cupboard or similar and not used often, maybe put them in mostly evacuated plastic zip lock bags with silica gel packets in the battery compartment.

Spot on! That's exactly what I do. I use 4 mil antistatic zip bags. I roll up the calculator in paper to avoid any possible plastic on plastic interaction, label it, then insert the package in the bag, roll the bag to evacuate most of the air, then seal it. I have over 200 machines preserved like this.
I plan to open the first calculator shop after the zombie apocalypse. =:0
Have to plan ahead, you know.
-J

[teenix]

I guess for environment concerns, some rice wrapped in a piece of an old cotton T-Shirt and made into a small parcel could replace the silica gel. Wash the shirt first though ;-)

[John Garza (3665)]

I place one of these in each bin:
Silica Canister

And while packing the machines in the bins, I crank the RH down to 40% in the lab, just for an added measure. I live near the Gulf Coast of TX, and it's usually humid. So I may seem a bit paranoid about humidity - but I'd rather be over cautious than under.

-J