HP-10 repair

[Benoit Maag]

I am working on restoring a beautiful HP-10 that succumbed to corrosion. See picture (after initial vinegar swapping). Is a dip into water+vinegar (which proportion?) the next step? How long? Or something else? Will that restore the darkened tracks? And should I be concerned about exposing the flex cable to vinegar?

Please advise,

[teenix]

It is probably best if you remove the ribbon cable and printer assembly before cleaning to avoid possible damage while handling the board during cleaning. I don't have access to the HP-10 so I don't know if the connector is similar to the 97 in that, you need a special tool (or make one) that will help in its removal. If it is the same, do not try to pull it out or you will damage it.

The black stuff is probably oxidized copper. If so, then the solder coating on the PCB tracks has probably also corroded over time. It might be hard to clean off without some sort of scrubbing with a tooth brush and perhaps a paste of baking soda and water. If the corrosion doesn't come off with the light scrubbing, I would just leave it there. Maybe the oxidized layer might protect the track remains under it.

One problem may occur with the corrosion removal, is that the remaining copper on the PCB tracks might wear through to the bare board. If this happens, you will have to create new tracks by soldering thin wires.

Try to avoid scrubbing the coil in the power supply part of the board or you might disturb the wiring causing a problem.

You might have to soak the end of the board for a few minutes in mild white vinegar solution where the chip is to hopefully dissolve any corrosion under it. This chip is probably sensitive to static discharge and may get damaged, so handle the board by the edges and don't go scuffing around carpets with pink fluffy slippers on while you are working on it.

The board can be flushed with warm water from a running tap and extra scrubbing with the tooth brush and then dried with a hair dryer as long as you do not over heat the board. Check the board carefully after drying as you might have to flush it again if you notice cleaning residue.

Once clean and dry, that corrosion will come back again and attack any exposed copper.

You can buy spray can circuit board lacquer (conformal coating) that will help protect it and you can solder through this stuff if need be. If you use this you will have to mask any connection points, (circuit board pins, ribbon socket etc) before using it. There are a few circuit board protection products available.

cheers

Tony