HP-29C now has dots across the display...

[Maximilian Hohmann]

Hello!

(09-02-2024 03:29 PM)AnnoyedOne Wrote:  From what I've seen most of these old Woodstock's have often been repaired in one way or another. A new (board to replace the ACT) CPU, batteries, power supply etc.

The reason for the repairs is usually battery leakage. The older calculators (like the HP-35) had a fully enclosed battery compartment inside wich an almost completely enclosed battery pack was placed. There is almost no chance for battery leakage to reach the calculator internals. The woodstocks still have that separate compartment but it has some openings. And the battery packs are not fully closed either. This results in an almost 100% chance of battery fluids reaching the PCB, componets and keyboard internals. Then there is this mediocre charging circuit which uses the battery itself for voltage regulation. A dead or poorly connected battery will result in overvoltage applied to the circuitry. No problem until the calculator is switched on. After that, death in an instant. And there is no proper charging current regulation with the power connector either. People who have the habit of leaving their devices plugged in all the time (no problem with modern devices apart from the unnecessary engery waste, but a cardinal sin when operating vintage machinery) will kill the batteries quickly. They keep charging and charging to the point when they start squirting their contents over those little microcontrollers...

(09-02-2024 03:29 PM)AnnoyedOne Wrote:  For my "experiment" I'd use a PSU with a current limit (set low) just in case.

That's not so easy because the LEDs require quite some current. Enough to fry the more delicate integrated circuits in case something is wrong.

Regards
Max