Dead HP 35

[Geoff Quickfall]

Prior to removing the ICs with suspect contamination, I will share with you an, albeit, anecdotal story.

Picked up an early 12C for $3. Don’t usually mess with 12C as they are still in production, but this was early American build.

The batteries were fused into a single cylinder from leakage. The leakage seeped in the top left quarter of the logic / keyboard PCA. After cleaning as much as possible with vinegar, mechanical picking (dental probe), then testing continuity on suspect traces I managed to resurrect a random display of nonsense on the LCD.

Aha, progress.

After much testing the display driver, affected by corrosion was the suspect. So, because Voyagers keyboards are not made to be disassembled without risking reassembly, I did a Katie Wasserman suggestion.

She mentioned that DeOxit red has an ability as an active deoxidizer, to “repair” ICs by mechanically weeping under the IC and the PCA board. This results in the corrosion being removed, thus isolating any traces that were shorted by the corrosion.

So I added quite a few drops of DeOxit red (squeeze bottle with needle) around the suspect IC and let it weep throughout the underside as an experiment.

Left it over night and the next day had 90% of the display left. By 48 hours the entire calc functioned as new! That was about 5 months ago. It is still fully functional today!

So, before major surgery try the DeOxit trick on the ICs at the display end and on the logic PCA IC’s, particularity around the suspect solder joints and ICs.

Geoff

Here is the link to the post on facebook.

DeOxit red and the HP 12C ca 1987