HP-19C Repair Odysee

[teenix]

(03-01-2021 10:26 PM)Don Williams Wrote:  So before I finally get back to this project I realize that I did not check the printer functions. So just before I close them up I connect the power supply to check the printers.

Are you ready for it?

I connected the bench power supply going to both calculators BACKWARDS. Smoked them both. The only good thing out of it was at least I did not have try to reassemble them again. That was about a dozen years ago. They still sit in their final resting state. I taped everything down in that final condition and sort of created a small shrine to my stupidity. May they rest in peace. And may I never see a 19C again. Miserable design.

I feel the pain, although I didn't destroy such a valuable item - touch wood.

A reversed biased diode in parallel with the power supply via a fuse might have saved the day.

Did it actually destroy itself. The power supply has diodes stopping the reversed voltage appearing in some circuit areas, and through the power supply coil.

The RAM attached to the battery has diode protection as well although not meant for the purpose.

Some items like tantallum caps in the power supply may have fried/shorted and stopped it working.

You never know your luck in a big city.

cheers

Tony